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The 2023-2024 snow season was generally underperforming, with long snowless stretches and few notable events across the United States. Some regions, like western mountain areas, saw exceptions with significant snowfall. The season was chronicled month-by-month in Weatherwise, highlighting noteworthy snow events and totals. Overall, snow cover extent was below normal for most of the season, with only a few exceptions in certain regions. [Extracted from the article]

Dispersal is a ubiquitous ecological process that has been extensively studied in many plants and animals. Anadromous salmonids are an interesting system for examining dispersal, in part because of their well‐known philopatric behaviour, but also because of the conservation challenges related to the dispersal of hatchery‐origin fish. Building on earlier work, we provide an updated systematic review of dispersal and gene flow in anadromous salmonids. In particular, we compared studies on the dispersal of anadromous salmonids from wild and hatchery origins, including studies providing estimates of dispersal rates, observations of dispersal and results from modelling studies. We reviewed 228 studies and found these were unevenly distributed among species, with Atlantic salmon, Chinook salmon and sea trout being well‐represented. Our results showcase considerable variability in estimated dispersal rates within and across studies, which is likely related to the different methodologies, dispersal propensities across species and populations, and spatial extents considered. Overall, our results confirmed a higher tendency of hatchery fish to disperse relative to wild fish, but we also found some variation across species that warrants further study. Moreover, we found that dispersal propensity tended to decline exponentially with distance and that the drivers of dispersal varied considerably among studies. Additionally, we highlight various facets of dispersal captured across this suite of studies, including variation in terminology, methods and metrics for characterising dispersal, and the spatio‐temporal scales considered. Finally, our review revealed that few studies considered, and even fewer assessed, the implications of dispersal for the conservation and management of anadromous salmonids. [ABSTRACT FROM AUTHOR]

Objective: To maximize harvest of hatchery steelhead Oncorhynchus mykiss and Pacific salmon Oncorhynchus spp. while reducing impacts to wild conspecifics, fishery managers rely on the ability of anglers to distinguish between the two. Fin erosion, including dorsal fin erosion, is a common result of hatchery rearing of juvenile salmonids. Since the 1980s, managers in the Pacific Northwest have utilized adult steelhead dorsal fin height as a regulatory control rule, requiring anglers to release steelhead with dorsal fins over a height threshold. This approach assumes that all or most hatchery fish have shorter dorsal fins than their wild counterparts. This study was designed to test this assumption. Methods: We compared steelhead origin (hatchery or wild) determined using scale analysis and adipose fin clipping (hatchery n = 127, wild n = 71) with origin estimated using dorsal fin height. Result: Overall, a static dorsal fin height threshold (2.25 in, 5.72 cm) correctly identified 90% of hatchery‐origin steelhead but misidentified nearly half (44%) of wild fish as hatchery. Dorsal fin height of known hatchery fish correlated with fish length, indicating a weakness of using a static dorsal height threshold as a management tool. The accuracy of distinguishing wild fish improved, but only marginally (56–76%), using a classification model where dorsal fin height of known origin fish from this study was a continuous predictor of origin. In comparison, adipose fin status correctly identified 97% of unmarked fish as wild. Conclusion: The low accuracy of the classification model and static dorsal fin height thresholds at distinguishing hatchery and wild steelhead due to a strong correlation between dorsal fin height and fork length and the high fork length variability of hatchery origin fish. Given the low cost and accuracy of adipose fin clipping and the potentially high conservation risk associated with misidentification, we recommend discontinuing the use of dorsal fin height as a harvest control rule for steelhead. Impact StatementOur study revealed that the dorsal fin height harvest control rule is inaccurate at distinguishing hatchery and wild steelhead, presenting a potentially high conservation risk and supporting the use of the highly accurate and low‐cost adipose‐fin‐clipping method. [ABSTRACT FROM AUTHOR]

Objective: Historically, most high mountain lakes in western North America were devoid of fish, but during the past century, many have been stocked with salmonids to diversify angling opportunities. Basic information on harvest and catch and release (C–R) for high mountain lake fisheries is lacking, as is information on factors influencing catch in such settings; our objectives were to fill these knowledge gaps. Methods: Using angling gear, we captured and implanted T‐bar anchor tags into 1163 salmonids of various species (fish of wild origin or hatchery fish stocked as fry; they could not be distinguished) in 103 high mountain lakes scattered across Idaho. Angler‐reported tag returns were used to estimate annual rates of exploitation and C–R, and a model selection approach was used to investigate factors influencing the angler catch of tagged fish. Result: Anglers reported the catch of 125 tagged fish from 52 different lakes. The mean number of days at large for reported fish was 318 days, with a range of 1 to 1465 days. Annual exploitation was 5.8 ± 7.1% (mean ± 90% confidence interval), the annual C–R rate was 8.5 ± 8.5%, and total annual catch (i.e., exploitation plus C–R) was 14.2 ± 11.0%. Of the predictive factors that we investigated, the likelihood of a fish being caught by an angler was negatively associated with hiking distance and positively associated with shoreline development index and fish length. Conclusion: Our results indicate that exploitation of salmonids in Idaho high mountain lakes is low even with liberal (six‐fish daily bag limit) harvest regulations. Consequently, angler harvest is unlikely to be substantively affecting the abundance or size structure of salmonid populations in these lakes. Continued tagging would improve the precision of exploitation and C–R estimates, especially for comparisons among species. Impact StatementBased on angler reporting of tagged fish, the annual exploitation of salmonids in Idaho high mountain lakes was 5.8% and the catch‐and‐release rate was 8.5%. Less hiking distance, a less uniform shoreline, and larger fish size improved the likelihood that tagged fish would be caught by anglers. [ABSTRACT FROM AUTHOR]

Throughout their native range, adfluvial brown trout populations have declined due to habitat degradation and over exploitation. As a consequence, numerous restoration projects that include stocking of hatchery‐reared trout have been conducted; however, estimates of survival in large lakes remain scarce. Here, we use telemetry to evaluate the survival of stocked trout smolts and sub‐adults in a large lake in central Sweden. Of the smolts released in the main tributary, 42% entered the lake. Both life stages suffered high rates of mortality. Only 8% of smolts survived the first 10 months after entering the lake and 10% of those released as sub‐adults survived 23 months post‐release. In agreement with studies on anadromous trout, we conclude that stocking of hatchery‐reared individuals is not an efficient method to recover population numbers due to poor performance in the wild. Similar studies from other large lakes and comparisons with wild conspecifics would increase the applicability of the results and promote further understanding of the utilization of hatchery‐origin trout to rebuild wild populations and sustain fisheries. [ABSTRACT FROM AUTHOR]

A 12-week feeding trial assessed the impact of protein-to-lipid ratios (P:L) on the growth, feed and protein utilization, digestive enzyme activity, and fillet composition of juvenile striped bass (Morone saxatilis) raised at summer local seawater temperature conditions (21 °C). A 3 × 2 factorial design, using three protein levels (40, 44, and 48%) and two lipid levels (12 and 16%) resulting in six diets (40:12, 44:12, 48:12, 40:16, 44:16, and 48:16) was used. Hatchery-reared fish with an initial weight of 11.4 ± 0.2 g were used. Laboratory-formulated experimental diets were randomly assigned to triplicate groups of 22 fish in 500-L tanks connected to a recirculating seawater (35.4 ± 3 ppt) system, and fish were fed manually to apparent satiation four times a day. Survival rates were higher than 96% across all treatments, remaining unaffected by dietary treatments. Fish fed the 44:12 and 48:12 diets resulted in significantly higher weight gain (WG) (274.1 ± 18.4 and 306.8 ± 19.8, respectively), final body weight (FBW) (42.4 ± 1.2 g and 47.1 ± 2.4 g, respectively), and specific growth rate (SGR) (1.6 ± 0.06 and 1.7 ± 0.06, respectively). Diets with 12% lipid resulted in feed conversion rate (FCR) values closer to 1, and the 48:16 (1 ± 0.03) treatment resulted in no significant differences compared to the 12% lipid dietary treatments. Similar trends were observed for protein efficiency ratio (PER), with comparable values for the 40:12 (2.0 ± 0.1), 44:12 (2.2 ± 0.1), 48:12 (2.0 ± 0.1), and 48:16 (2.1 ± 0.1) treatments. A strong relationship between dietary P:E ratios and SGR, PER, and FCR was observed among treatments, which helped explain the interactions between protein and lipid obtained. An estimated dietary P:E ratio between 11 and 12 is suggested for efficient protein and feed utilization for this species under our culture conditions. The apparent digestibility coefficient (ADC %) was significantly higher in the 12% lipid diets (65.01 ± 3.06%), influenced solely by lipid content. Enzyme activity for trypsin and chymotrypsin in the pyloric caeca (PC) and intestines (I) were higher in the 48:12 treatment (893.5 ± 18.1, 1087.3 ± 55.5, 12.2 ± 0.3, and 8.3 ± 0.2 Units/g organ, respectively). L-aminopeptidase activity (PC) was higher in the 48:12 treatment (1007.7 ± 101.8 Units/g organ), while L-aminopeptidase (I) had higher values in the 48:16 treatment (2217.2 ± 161.3 Units/g organ). In the case of lipase (PC), activity was higher in the 12% lipid treatments, while in the intestine, the highest activity was recorded in the 44:12 treatment (1084.4 ± 87.0). The activity of proteases, except for L-aminopeptidase (PC), directly correlated with improvements in SGR, PER, feed intake (FI), and FCR which helps explain the observed results. The Hepatosomatic index (HSI) was significantly higher in the 40:12 treatment while the liposomatic index (LSI) and viscerosomatic index (VSI) indices showed no significant differences between the 40:12, 44:12, 48:12, and 48:16 treatments, respectively. Importantly, the lipid content in the fillet did not significantly decrease with reduced lipid content in the diet, an important issue for market acceptance. Results from the present study suggest an optimal P:L ratio of 48:12 for juvenile striped bass raised in seawater under local summer conditions (21 °C). [ABSTRACT FROM AUTHOR]

The study involved three groups of six broodstock with a 1:1 male-to-female ratio. They were injected with 13 µg/kg LHRHa to stimulate spawning. We fed the broodstock three diets: a control diet without selenium, a diet containing 0.3 mg of nano-selenium /kg (N-Se), and a diet containing 4 mg of organic selenium /kg (O-Se). The broodstock diet consisted of equal parts of dry feed (45% protein), sardines, and squid. After being laid, the eggs were obtained from the collection ponds at the General Authority for Fisheries Development's fish hatchery and incubated until hatching. The larvae were given a micro diet containing 51.7% crude protein and live food (Rotifer and Artemia). Rotifer density increased from 5/ml to 15/ml by day 22 dph, Artemia nauplii increased from 0.2 to 4 ind./ml, from 7 to 35 dph then decreased to 0 at 55 dph, and micro-diets increased from 100-200 µ at 16 dph to 200-400 µ at 23-40 dph to 300-500 µ at 55 dph, and 500-1000 µ until the experiment ended. Three different diets in three replicates were tested: A micro diet free of selenium as a control diet (C), A micro diet with 0.3 mg of nano selenium (N-Se) kg-1, and A micro diet supplemented with organic selenium 4 mg (O-Se). Each group was taken from the three Broodstock groups respectively. Sixteen days after hatching, the three experimental micro diets were introduced to the larvae and continued for 76 days post-hatch. Larvae (260,000 per tank) were placed in fiberglass tanks with 4 m3 of water at a temperature of 19±2°C for optimal conditions. The larvae fed the N-Se diet had significantly better survival rates (75.0 ± 1.2 %), final body weight (240.0 ± 5.8 mg), weight gain (239.00 ± 5.8 mg), average daily gain (3.98±0.1mg), total length (39.0±0.06 mm), specific growth rate (9.133±0.04 %/day), feed intake (471.67±0.01 mg), and better feed conversion ratio (1.97±0.01) than the other groups (P < 0.05). The group provided with N-Se also had the highest levels of glutathione peroxidase enzyme (GPx) content in the whole larval body, whereas the control diet without Se supplementation recorded the lowest value of (14.8 ± 0.1 U/mg protein). The number and length of folds in the stomach and esophagus of sea bass post-larvae fed on diets fortified with selenium in both forms, nanoparticles or organic, showed a significant (P < 0.05) enhancement on the larval gastrointestinal (GI) tract. Moreover, selenium has an anti-inflammatory action in sea bass post-larvae. This study concluded that using N-Se as an antioxidant supports the growth and survival of European seabass D. labrax, gastrointestinal development and antioxidant efficacy during critical weaning. [ABSTRACT FROM AUTHOR]

Intraspecific biodiversity is vital for species persistence in an increasingly volatile world. By embracing methods that integrate information at different spatiotemporal scales, we can directly monitor and reconstruct changes in intraspecific biodiversity. Here we combined genetics and otolith biochronologies to describe the genotypic and phenotypic diversity of Chinook salmon (Oncorhynchus tshawytscha) in the Yuba River, California, comparing cohorts that experienced a range of hydroclimatic conditions. Yuba River salmon have been heavily impacted by habitat loss and degradation, and large influxes of unmarked hatchery fish each year have led to concern about introgression and uncertainty around the viability of its wild populations, particularly the rarer spring‐run salmon. Otolith strontium isotopes showed that Yuba River origin fish represented, on average, 42% (range 7%–73%) of spawners across six return years (2009–2011, 2018–2020), with large interannual variability. The remainder of adult Chinook salmon in the river were primarily strays from the nearby Feather River hatchery, and since 2018 from the Mokelumne River hatchery. Among the Yuba‐origin spawners, on average, 30% (range 14%–50%) exhibited the spring‐run genotype. The Yuba‐origin fish also displayed a variety of outmigration phenotypes that differed in the timing and size at which they left the Yuba river. Early‐migrating fry dominated the returns (mean 59%, range 33%–89%), and their contribution rates were negatively correlated with freshwater flows. It is unlikely that fry survival rates are elevated during droughts, suggesting that this trend reflects disproportionately low survival of larger later migrating parr, smolts, and yearlings along the migratory corridor in drier years. Otolith daily increments indicated generally faster growth rates in non‐natal habitats, emphasizing the importance of continuing upstream restoration efforts to improve in‐river growing conditions. Together, these findings show that, despite a long history of habitat degradation and hatchery introgression, the Yuba River maintains intraspecific biodiversity that should be taken into account in future management, restoration, and reintroduction plans. The finding that genotypic spring‐run are reproducing, surviving, and returning to the Yuba River every year suggests that re‐establishment of an independent population is possible, although hatchery‐wild interactions would need to be carefully considered. Integrating methods is critical to monitor changes in key genetic, physiological, and behavioral traits to assess population viability and resilience. [ABSTRACT FROM AUTHOR]

A refugial population of the endangered delta smelt (Hypomesus transpacificus) has been maintained at the Fish Conservation and Culture Laboratory (FCCL) at UC Davis since 2008. Despite intense genetic management, fitness differences between wild and cultured fish have been observed at the FCCL. To investigate the molecular underpinnings of hatchery domestication, we used whole‐genome bisulfite sequencing to quantify epigenetic differences between wild and hatchery‐origin delta smelt. Differentially methylated regions (DMRs) were identified from 104 individuals by comparing the methylation patterns in different generations of hatchery fish (G1, G2, G3) with their wild parents (G0). We discovered a total of 132 significant DMRs (p <.05) between G0 and G1, 132 significant DMRs between G0 and G2, and 201 significant DMRs between G0 and G3. Our results demonstrate substantial differences in methylation patterns emerged between the wild and hatchery‐reared fish in the early generations in the hatchery, with a higher proportion of hypermethylated DMRs in hatchery‐reared fish. The rearing environment was found to be a stronger predictor of individual clustering based on methylation patterns than family, sex or generation. Our study indicates a reinforcement of the epigenetic status with successive generations in the hatchery environment, as evidenced by an increase in methylation in hypermethylated DMRs and a decrease in methylation in hypomethylated DMRs over time. Lastly, our results demonstrated heterogeneity in inherited methylation pattern in families across generations. These insights highlight the long‐term consequences of hatchery practices on the epigenetic landscape, potentially impacting wild fish populations. [ABSTRACT FROM AUTHOR]

Large dam removal is being used to restore river systems, but questions remain regarding their outcomes. We examine how the removal of two large dams in the Elwha River, coupled with hatchery production and fishing closures, affected population attributes of Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss). Initial responses by returning adult Chinook salmon and steelhead was an increase in the number and spatial extent of natural and hatchery origin fish. Although few naturally produced juvenile Chinook salmon and steelhead outmigrants were observed prior to and during dam removal, abundances increased three years after adult fish passage was restored, suggesting that impacts due to downstream sedimentation after dam removal were reduced. The Chinook salmon population demographics remain dominated by hatchery production, while increases in winter steelhead abundance included both hatchery and natural-origin spawners. The spatial expansion of winter steelhead upstream of former dam sites was predominantly by natural-origin spawners. We also observed a natural "reawakening" of summer steelhead that were in part derived from an up-river resident population that returned to the Upper Elwha. Our results showed that a combination of habitat, hatchery, and harvest actions can result in positive responses for salmonid populations. [ABSTRACT FROM AUTHOR]

Infectious diseases are a leading cause of losses in the aquaculture industry and conservation programs globally. Simultaneously, infectious diseases pose a substantial risk to fish being hatchery-reared and released into natural habitats for conservation purposes, including the Great Lakes lake sturgeon (Acipenser fulvescens, i.e., GL-LST). Recently, an alloherpesvirus (lake sturgeon herpesvirus 2, i.e., LSHV-2) capable of inducing disease and/or mortality in adult and juvenile GL-LSTs was detected in two adult GL-LST populations. To begin developing disease prevention and/or control methods, in vitro experiments were designed to determine the susceptibility of LSHV-2 to disinfectants commonly used in hatchery and aquaculture facilities (Virkon®-Aquatic: potassium peroxymonosulfate; Ovadine®: polyvinylpyrrolidone iodine complex; and Perox-Aid®: hydrogen peroxide). Cultured LSHV-2 was exposed to each disinfectant at two concentrations (Virkon®-Aquatic: 0.5% and 1%; Ovadine®: 50 and 100 ppm; and Perox-Aid®: 500 and 1000 ppm) in duplicate for durations of 1, 10, and 30 min. Following exposure, the disinfectant was neutralized, and after a 14-day incubation period on a white sturgeon × lake sturgeon hybrid cell line (WSxLS), percent reduction was calculated by comparing the 50% tissue culture infectious doses (TCID50/mL) of the virus with and without disinfectant exposure. When exposed to Perox-Aid®, LSHV-2 percent reduction ranged from 58.7% to 99.5%. When exposed to Ovadine®, the percent reduction ranged from 99.4% to 100%. Lastly, the percent reduction when exposed to Virkon®-Aquatic was 100% for both concentrations and all timepoints. The results herein provide evidence that both Virkon®-Aquatic and Ovadine® are virucidal to LSHV-2 and may represent a means to reduce virus transmission risk under field settings. [ABSTRACT FROM AUTHOR]

Introgression of non‐native conspecifics changes the genetic composition of wild populations, potentially leading to loss of local adaptations and fitness declines. However, long‐term data from wild populations are still relatively few. Here, we studied the effects of introgression in a Danish brown trout (Salmo trutta, L.) population, subjected to intensive stocking with domesticated hatchery fish of non‐native origin. We used wild‐caught genetically wild and admixed trout as well as fish from the partly domesticated hatchery strain used for stocking the river up until ~15 years prior to this study, to produce 22 families varying in hatchery/wild admixture. Following a replicated common‐garden experiment conducted in fish tanks from first feeding through 23 weeks at 7, 12, and 16°C, we observed a significant positive relationship between family admixture and fish size upon termination, an effect observed through all levels of admixture. Furthermore, the admixture effect was most distinct at the higher rearing temperatures. Although the hatchery strain used for stocking had been in culture for ~7 generations, it had not been deliberately selected for increased growth. These data thus demonstrate: (i) that growth had increased in the hatchery strain even in the absence of deliberate directional selection for this trait, (ii) that the increasing effect of admixture by temperature could represent inadvertent selection for performance in the hatchery strain at higher temperatures, and most significantly, (iii) that despite undergoing up to five generations of natural selection in the admixed wild population, the genetically increased growth potential was still detectable and thus persistent. Our findings suggest that altered growth patterns and potentially their cascading effects are of importance to the severity of hatchery/wild introgression, especially under changing‐climate scenarios and are of general significance to conservation practitioners seeking to evaluate long‐term effects of intra‐specific hybridization including under recovery. [ABSTRACT FROM AUTHOR]

Moina sp. recently has attracted the interest of hatchery operators because it is a renewable resource and has a low production cost. The effect of live and frozen forms of Moina in replacing Artemia during the larval rearing of river catfish, Pangasius nasutus, Bleeker, 1863, was investigated for 21 days. The eight-day-old posthatchling larvae were fed with live Moina (LM), frozen Moina (FM), and live Artemia (LA), of which LA served as control. The feeding trials were done in triplicate. There was no significant difference in the final mean weight and specific growth rate between all treatments. However, the larvae exhibited significantly (P <.05) higher survival when fed with LM (27.2 ± 1.1%) against LA (15.9 ± 3.9%) and FM (1.1 ± 0.7%). As a conclusion, live Moina could be used to replace Artemia in the larval rearing of P. nasutus based on comparable growth performance and improved survival. [ABSTRACT FROM AUTHOR]

This research aims to determine the optimal dose of boiled mackerel tuna mixture on HI-PRO VITE 781 feed on gonadal maturity index and feed conversion ratio of transgenic mutiara catfish G4 in indoor hatchery maintenance at optimal temperature. This research was conducted at the Hatchery of the Faculty of Fisheries and Marine Sciences, Universitas Padjadjaran. The method used was an experimental method with a completely randomized design (CRD) method with four treatments, namely the difference in the dose of boiled mackerel tuna administration in comercial feed and three replications. The treatment in this study was the administration of boiled mackerel tuna doses of 3.5%, 2.5%, 1.5% in mixed feeds to G4 transgenic mutiara catfish and tested on non-transgenic mutiara catfish with a percentage of 3.5% female weight biomass and then added an 30 g HI-PRO-VITE 781 with two times feeding frequency. The research parameters included gonad maturity index and feed conversion ratio. The results showed that feeding a mixture of boiled mackerel tuna and HI-PRO-VITE 781 had a significant effect on the gonadal maturity index and feed conversion ratio. Feeding boiled mackerel tuna at 1.5% was the best treatment with a gonadal maturity index of 47.16% for females and 4.98% for males and a feed conversion value of 1.19 for 56 days of rearing. [ABSTRACT FROM AUTHOR]

Purpose. To analyze the effect of the main hydrochemical parameters in the nursery ponds of the Kherson production and experimental hatchery for the cultivation of common freshwater fish on the quality of fish seeds. Methodology. Studies of hydrochemical parameters of the first-order nursery ponds (No. 2, 3, 9, 10, 11, 12, 13, 15, 16) were carried out at the Kherson production and experimental hatchery for the cultivation of common freshwater fish. Collection of hydrochemical water samples was carried out during the growing season of 2021 from spring to autumn. During the study, a total of 81 samples were processed in 9 ponds (an integrated sample from three sites of the pond) according to 14 physicochemical parameters, which included the gas regime, physical properties, mineral and ionic composition of water, the content of biogenic, organic and specific pollutants. Chemical analysis of water samples was performed in the field with a Palintest 7100 multiparametric photometer and the laboratory of the Kherson State Agrarian and Economic University, Department of Water Bioresources and Aquaculture. Concentrations of oxygen, free hydrogen ions and water temperature were determined with a portable multimeter AZ86031. The fish seeds were studied to determine the average weight, linear growth, gut fullness index, and Fulton's condition factor. The material was processed in a quantitative-weight way by individual review of digestive tracts. At the same time, fat content, color of food, degree of gut fullness was determined. Findings. The article examines the effect of the hydrochemical regime of the ponds of the Kherson production and experimental hatchery for the cultivation of common freshwater fish on the quality of fish seeds. The main hydrochemical parameters of nursery ponds, growth, length and weight parameters, gut fullness index, Fulton's condition factor during the cultivation of fish seeds were analyzed, and an assessment of these parameters was carried out. It was established that the water in the ponds throughout the year was significantly saturated with organic and biogenic substances. In a number of ponds, an excess of bichromate oxidation, biological oxygen consumption, and periodically - permanganate oxidation was constantly recorded. The peak of organic water pollution falls on the summer-autumn period. At this time, the content of nitrogen-containing compounds, phosphates, and total iron increased, water bloom was observed, and cases of dissolved oxygen deficiency were recorded, which negatively affected the quality of fish seeds - silver and bighead carps. The main cause of oxygen deficiency is its active consumption by hydrobionts and costs for the oxidation of organic substances in water. The dynamics of the increase in the total mineralization of water in the ponds from spring to autumn were monitored. The natural genesis of this process has been established and the possible risks that may arise during the cultivation of fish seeds in connection with the specified dynamics of mineralization throughout the year have been assessed. As a result of the cultivation of fish seeds according to length and weight parameters, the index of gut fullness and fatness, a decrease in the intensity of growth and weight gain of silver and bighead carps was established, their values at the end of October were within the normative limits - 20 g (l = 11.56 cm, Q = 20.18 g), while the increase in almost three months (August - October) amounted to only 5 g. The reason for this is a decrease in the general index of gut fullness from June to September, respectively, these values in July averaged 129.250/000, in August there was a decrease to 91.90/000, in September the lowest va.ue was 500/000 The condition factor reflected a similar situation, a decrease from mid-summer to late September ranging from 1.64 to 1.30. This phenomenon indicates low feeding activity in this period, which we associate with the deterioration of the hydrochemical state of the water in the nursery ponds. Originality. Modern data on the main parameters of the hydrochemical regime of nursery ponds are presented. The relationship between organic pollution in the summer-autumn period, an increase in the content of nitrogen-containing compounds, phosphates, total iron, a deficiency of dissolved oxygen and the quality of fish seeds was established. The obtained results demonstrate the actual values of the hydrochemical state of the studied objects, in particular, the oxygen regime of the ponds has dynamics opposite to the dynamics of the content of organic substances. Practical Value. The analysis of the dynamics of the most significant elements of the hydrochemical regime of nursery ponds and the establishment of a close relationship between it and the phases of the technological processes of growing fish seeds leads to the shortening of the cycle of cultivation. Considering the tendency a decrease in the condition factor and gut fullness index from mid-summer of all cultivated fish species, there is a proposal to reduce the technological cycle of growing fish seeds until the end of August, when common and grass have values within the standard at the level of 22.68 g for grass carp, 35.18 g for common carp, while silver and bighead carps below normative values at the level of 15.0 g. Such a reorientation will allow reducing the costs of growing fish seeds by almost three months and to carry out the introduction in the period when it has the best adaptation and compensatory indicators. [ABSTRACT FROM AUTHOR]

Objective: As a type of automatic feeder, demand feeders reduce labor costs and can improve fish‐rearing efficiencies. However, mounting demand feeders can be problematic because of the variety of nonstandardized fish‐rearing units. This article describes an innovative, simple, sturdy, and durable demand feeder mount for rectangular, concrete raceways. Methods: The feeder mount was made from aluminum and sits flat on a raceway wall or walkway. A horizontal base plate, secured to the wall by vertical plates, holds a vertical riser of aluminum tubing. Attached to this tubing is a rod that secures the demand feeder. Result: This feeder mount design has proven durable over several years of actual use. Over this time, it has needed no maintenance other than occasional cleaning with water to remove spilled fish food. The feeder can be easily and quickly removed from the mount by simply pulling a pin and sliding the feeder off of the tubing. The mount is constructed to dramatically reduce tripping hazards and occupational safety and health risks. Conclusion: This simple, inexpensive (~US$50 to construct), and no‐maintenance mount is a viable solution to the typically difficult problem of mounting demand feeders to concrete raceways used for trout production. Impact statementThis article describes a relatively simple, inexpensive, no‐maintenance, and safe solution to the typically difficult problem of mounting demand feeders to concrete raceways used for fish production. [ABSTRACT FROM AUTHOR]

Objective: Conservation propagation facilities in the upper basin of the Missouri River are currently experiencing inconsistent survival of first‐feeding larval Pallid Sturgeon Scaphirhynchus albus among genetic families (i.e., distinct male–female pairings). The inconsistent survival can have unintended negative consequences for genetic representation of Pallid Sturgeon that are returned to the Missouri and Yellowstone rivers. We conducted a laboratory study designed to determine whether a live diet improves survival and growth of first‐feeding larval Pallid Sturgeon. Methods: First‐feeding larval Pallid Sturgeon from three distinct genetic families were assigned to one of the following diets: live first instar brine shrimp (Artemia franciscana) nauplii, an Otohime dry diet, a 50–50% combination of Otohime and live first instar brine shrimp nauplii, or food restricted (no food). Mortality was evaluated at the end of each day and at the end of the trial (21 days after the onset of exogenous feeding), and individual weight (g) was measured at the end of the trial. Result: Pallid Sturgeon larvae that received a live diet (either solely live first instar brine shrimp nauplii or the combined diet) experienced higher survival than larvae that were fed solely Otohime. Furthermore, there was statistical evidence that larvae receiving solely live first instar brine shrimp nauplii were heavier at 21 days postexogenous feeding than larvae that were fed either solely Otohime or the combined diet. Conclusion: Our results suggest that a live diet can improve survival and growth of first‐feeding larval Pallid Sturgeon at conservation propagation facilities. Impact statementLive diets improved the survival and weight of first‐feeding larval Pallid Sturgeon and can be incorporated into feeding regimens at conservation propagation hatcheries. [ABSTRACT FROM AUTHOR]

Successful aquacultural production of juvenile fish requires that the optimal rearing conditions be applied. However, for many fish species, there is a significant knowledge gap concerning these conditions. In this study, we evaluated the effects of stocking density on the survival and growth of brown meagre, Sciaena umbra (L.), during rearing trials in an experimental hatchery. This research forms part of a feasibility project to improve the aquacultural production of brown meagre. Four initial larval density treatments (5, 10, 30, and 70 larvae per L) were established. At 0, 9, 17, 22, and 25 days post-hatching, we measured the total length, coefficient of variation in length, and specific growth rate. The physicochemical water parameters remained at satisfactory levels for fish culture throughout the experiment. Lower densities promoted better growth in terms of total length, specific growth rate, and survival. We observed a significant negative correlation between larval density and length growth/survival. Thus, the low larval density treatment yielded the highest survival (48.5% ± 3.46%), growth in final total length (11.9 ± 1.09 mm), and specific growth rate (5.13% ± 0.39% per day). Increased stocking density therefore negatively affects growth and survival, reduces homogeneity, but increases the production of S. umbra larvae. This study helps identify optimal aquaculture conditions for maximizing the production of juvenile S. umbra for ecological restoration. [ABSTRACT FROM AUTHOR]

Simple Summary: Our findings highlight significant distinctions in body coloration between wild and hatchery-reared individuals, and a ten-day rearing period under colored ambient light can notably change the coloration of hatchery-reared marbled rockfish. Additionally, our research reveals a preference among juvenile marbled rockfish for a red-light environment, alongside a consistent negative phototactic response to yellow and blue light colors. These results emphasize the substantial influence of hatchery rearing conditions on fish body color and morphological color-changing abilities, and elucidate ambient light color preferences. Our study emphasizes the importance of considering modifications to the hatchery environment, particularly in regulating ambient light color, within stock enhancement programs. Hatchery rearing significantly influences the phenotypic development of fish, with potential adverse effects for the post-release performance of hatchery-reared individuals in natural environments, especially when targeted for stock enhancement. To assess the suitability of releasing hatchery-reared fish, a comprehensive understanding of the phenotypic effects of captive rearing, through comparisons with their wild conspecifics, is essential. In this study, we investigated the divergence in body coloration between wild and hatchery-reared marbled rockfish Sebastiscus marmoratus. We examined the selection preferences for different light colors and assessed the impact of different ambient light colors on the morphological color-changing ability of juvenile marbled rockfish. Our findings revealed significant differences in body color between wild and hatchery-reared marbled rockfish. The hue and saturation values of wild marbled rockfish were significantly higher than those of their hatchery-reared counterparts, indicative of deeper and more vibrant body coloration in the wild population. Following a ten-day rearing period under various light color environments, the color of wild marbled rockfish remained relatively unchanged. In contrast, hatchery-reared marbled rockfish tended to change their color, albeit not reaching wild-like coloration. Light color preference tests demonstrated that wild juvenile marbled rockfish exhibited a preference for a red-light environment, while hatchery-reared individuals showed a similar but weaker response. Both wild and hatchery-reared marbled rockfish displayed notable negative phototaxis in the presence of yellow and blue ambient light. These results highlight the impact of hatchery rearing conditions on the body color and morphological color-changing ability, and provide insight into light color selection preferences of marbled rockfish. To mitigate the divergence in phenotypic development and produce more wild-like fish for stocking purposes, modifications to the hatchery environment, such as the regulation of ambient light color, should be considered. [ABSTRACT FROM AUTHOR]

Hatchery fish and their offspring (including hatchery‐wild hybrids) have lower reproductive success than wild fish. Thus, the straying of hatchery fish may negatively impact wild populations, depending on the number of wild salmon returning and hatchery strays. We investigated the straying status of hatchery‐origin pink salmon (Oncorhynchus gorbuscha), which have a higher straying rate than other salmonids, in an unstocked river at the Shiretoko World Natural Heritage Site, Japan. The hatchery strays accounted for 40.0% and 19.0% of the total samples in 2021 and 2022, respectively. These results indicate that hatchery pink salmon have invaded unstocked rivers and potentially genetically affect wild populations. [ABSTRACT FROM AUTHOR]

Selection pressures differ along environmental gradients, and traits tightly linked to fitness (e.g., the visual system) are expected to track such variation. Along gradients, adaptation to local conditions might be due to heritable and nonheritable environmentally induced variation. Disentangling these sources of phenotypic variation requires studying closely related populations in nature and in the laboratory. The Nicaraguan lakes represent an environmental gradient in photic conditions from clear crater lakes to very turbid great lakes. From two old, turbid great lakes, Midas cichlid fish (Amphilophus cf. citrinellus) independently colonized seven isolated crater lakes of varying light conditions, resulting in a small adaptive radiation. We estimated variation in visual sensitivities along this photic gradient by measuring cone opsin gene expression among lake populations. Visual sensitivities observed in all seven derived crater lake populations shifted predictably in direction and magnitude, repeatedly mirroring changes in photic conditions. Comparing wild-caught and laboratory-reared fish revealed that 48% of this phenotypic variation is genetically determined and evolved rapidly. Decreasing intrapopulation variation as environments become spectrally narrower suggests that different selective landscapes operate along the gradient. We conclude that the power to predict phenotypic evolution along gradients depends on both the magnitude of environmental change and the selective landscape shape. [ABSTRACT FROM AUTHOR]

Simple Summary: Hatchery-reared Rainbow trout are released into freshwater systems, often to support recreational fishing, but the best age to release fish to maximise their chances of survival is unknown. Using laboratory tests of fish behaviour at six ages, we report age-related changes in emergence, exploration, food neophobia, habitat choice and predator avoidance. We suggest that an understanding of age-related changes in behaviour should be applied to support management decisions around the best age to release Rainbow trout. Millions of hatchery-reared Rainbow trout are currently released in Australian waters to support recreational fisheries objectives, yet many of these fish die soon after release. In addition, little is known whether these fish harbour parasites that can potentially threaten freshwater ecosystems and human health. Here, we tested the behaviour of hatchery-reared trout using six tank-based tests at six different ages to evaluate their chances of survival and then dissected fish to investigate parasite prevalence. At 7 weeks of age fish readily emerged from a hide and showed the greatest number of startle responses to predators. Behaviour around 25–29 weeks of age was relatively "shy", staying in shelter and avoiding open water. At around 37–41 weeks of age though, behaviour changed, with fish emerging from a hide more readily and exploring the environment. Interestingly, at 58 weeks of age fish were slower to initiate exploration, possibly indicating a return to "shyer" behaviour. All fish underwent thorough parasite examination, revealing no infections. We conclude that knowledge of the behaviour of hatchery-reared fish at different ages is useful for decisions around the timing of release that balance the needs of recreational fishers whilst managing the impact on freshwater ecosystem. [ABSTRACT FROM AUTHOR]

Water diversions worldwide may entrain or impinge fish and have population‐level impacts, but barriers like fish screens can reduce such threats. Traditional barriers are ineffective in the San Juan River, USA, due to high sediment and debris loads, so the Hogback Diversion Canal, NM, employs a novel weir wall design to reduce entrainment of sub‐adult and adult fishes. We evaluated the effectiveness of the weir wall in reducing the entrainment of larval fish using a combination of experimental and overnight trials. Larval fish densities were compared between the irrigation canal that delivers water to irrigators and subsequently entrains fish and the bypass canal that conveys water and fish back to the river. The density of hatchery‐produced larval fish collected in the irrigation canal during the experimental trial (0.74 fish/m3) was 52% of their density in the bypass canal (1.43 fish/m3), suggesting entrainment reduction. The density of wild‐produced larvae during overnight trials indicated some minor, mostly nonsignificant, differences between catch rates in irrigation and bypass canals, ontogenetic phases, and sampling dates. Though entrainment rates of wild‐produced larvae were not significantly reduced, density differences among postflexion mesolarvae and metalarvae suggest possible entrainment reduction of more developed ontogenetic phases. More intensive research is necessary to better elucidate the efficacy of the novel weir wall for reducing the entrainment of larval fish. However, our larval fish results and the results from prior large‐bodied entrainment studies suggest the novel weir wall may reduce fish entrainment in water diversions and benefit fluvial ecosystems in which traditional screens are unfeasible. [ABSTRACT FROM AUTHOR]

Endangered wild fish populations are commonly supported by hatchery propagation. However, hatchery‐reared fish experience very different selective pressures compared to their wild counterparts, potentially causing genotype‐by‐environment interactions (G × E) in essential fitness traits. We experimentally studied early selection in a critically endangered landlocked Atlantic salmon population, first from fertilization to the swim‐up stage in a common hatchery setting, and thereafter until the age of 5 months in two contrasting rearing environments. Swim‐up progeny were moved either to standard indoor hatchery tanks involving conventional husbandry or to seminatural outdoor channels providing only natural food. After the first summer, sampled survivors were assigned to their families by genotyping. Early survival until the swim‐up stage was mostly determined by maternal effects, but also involved significant variation due to sires and full‐sib families (potential genetic effects). High on‐growing survival in hatchery tanks (88.7%) maintained a more even distribution among families (relative share 1.5%–4.2%) than the seminatural environment (0.0%–5.4%). This heterogeneity was mostly maternal, whereas no independent paternal effect occurred. Heritability estimates were high for body size traits in both environments (0.62–0.69). Genetic correlations between the environments were significantly positive for body size traits (0.67–0.69), and high body condition in hatchery was also genetically linked to rapid growth in the seminatural environment (0.54). Additive and phenotypic growth variation increased in the seminatural environment, but scaling effects probably played a less significant role for G × E, compared to re‐ranking of genotypes. Our results suggest that not only maternal effects, but also genetic effects, direct selection according to the environmental conditions experienced. Consistently high genetic variation in growth implies that, despite its low overall genetic diversity and long history in captive rearing (>50 years), this landlocked Atlantic salmon population still possesses adaptive potential for response to change from hatchery rearing back to more natural conditions. [ABSTRACT FROM AUTHOR]

The California Central Valley steelhead (Oncorhynchus mykiss) has declined precipitously since Euro-American colonization and has been listed as threatened under the United States Endangered Species Act since 1998. Hatchery-origin fish now dominate the population, and hatchery management is a key listing factor. However, scant release metric information is available. We compiled a time series of O. mykiss hatchery release data for all four Central Valley hatcheries releasing O. mykiss between 1948 and 2017. The biocomplexity of released fish has declined since the early 1980s. Individuals have been released at increasingly similar numbers, biomass, body sizes, times, and locations over time. Moreover, yearling fish have been released at larger sizes, leading to the near-exclusive release of age-1 smolts in February and March since the late 1990s and early 2000s. Pervasive reductions in release portfolios have likely occurred for other hatchery-supported Pacific salmonid stocks throughout the Pacific Rim region. In an increasingly variable environment, such reductions in intraspecific diversity could significantly affect population stability and resilience. [ABSTRACT FROM AUTHOR]

Objective: An assumption of biotelemetry is that animal performance is unaffected by the tagging process and tag burden, yet this assumption is often untested or not thoroughly explored. Our objective was to explore how transmitter implantation procedures influenced Atlantic Salmon Salmo salar smolt survival and migratory performance. Methods: We monitored radio-tagged smolts, first in the hatchery and then in a river with a receiver array. We assessed survival and in-river performance in relation to surgeon, surgery duration, processing order, and fish size. Result: Mortality was 13.3% during an 8-day hatchery-observation period but was higher for fish that were processed by one of two experienced surgeons (25% vs. 2%). Mortality peaked 3 days postsurgery and was higher for smaller fish and fish that were tagged during morning tagging sessions (versus afternoons). The size effect changed over time, being greatest during the first 2 days postsurgery and continuing thereafter at a diminished level. Fish performance once released into a river also differed between surgeons (migration initiation 66% vs. 82%; to-lake migration success 22% vs. 43%) and, consistent with hatchery observations fish that were tagged in the morning by one surgeon, performed poorly once released. Conclusion: We highlight the immediate and lingering effects of surgical procedures on smolt survival that, if not accounted for, could bias inferences about the study population. Researchers should anticipate tagger effects during study design to ensure potential tagger effects (i.e., surgeon, order tagged, conditions during tagging) are balanced across study groups of interest. Testing for a fixed tagger effect in analyses may not always be adequate because a tagger effect may covary with processing order and fish size and may change over time. [ABSTRACT FROM AUTHOR]

Several countries have implemented stocking programmes to enhance abundance and fish production by releases of hatchery-reared fish. However, due to fluctuations in population size, stocking history, and potential indirect effects of straying of hatchery-reared fish, it is often difficult to predict how these factors will affect genetic diversity and differentiation patterns among wild populations. This study characterized the population genetic structure and temporal variability of four Estonian sea trout populations by evaluating the degrees of direct and indirect genetic impacts of stocking over two decades using 14 microsatellite loci. Our results demonstrate considerable temporal change combined with weak genetic structuring among studied sea trout populations. We found a reduction of the overall level of genetic differentiation combined with the tendency for increased genetic diversity, and an effective number of breeders (Nb) over the study period. Furthermore, we found that immigration rates (m) from hatchery stocks were highest in the population subjected to direct stocking and in non-stocked populations that were located geographically closer to the stocked rivers. This work suggests that hatchery releases have influenced the genetic diversity and structuring of studied sea trout populations. However, the impact of hatchery releases on the adaptive variation and fitness-related traits in wild trout populations remains to be revealed by more informative genetic markers. This study illustrates the dynamic nature of the population genetic structure of sea trout and the value of long-term genetic monitoring for management and conservation. [ABSTRACT FROM AUTHOR]

The aquaculture industry has rapidly grown over the year. One pertinent aspect is the ability of the aquaculture farm management to accurately count the fish populations to provide effective feeding and the control of breeding density. The current practice of counting the fish manually increased the hatchery workers workload and led to inefficiency. The presented work proposed an intelligent, web-based fish counting system to assist hatchery workers in counting fish from images. The methodology consists of two phases. First, an intelligent fish counting engine is developed. The captured image was first enhanced using the contrast limited adaptive histogram equalization. A deep learning architecture in the form of you only look once (YOLO)v5 is used to generate a model to identify and count fish on the image. Second, a web-based application is developed to implement the developed fish counting engine. When applied to the test data, the developed engine recorded a precision of 98.7% and a recall of 65.5%. The system is also evaluated by hatchery workers in the University Malaysia Sabah fish hatchery. The results of the usability and functionality evaluations indicate that the system is acceptable, with some future work suggested based on the feedback received. [ABSTRACT FROM AUTHOR]

The culture of African catfish, Clarias gariepinus, is constrained by the high mortality of fry, occasioning a shortage of high-quality seeds for stocking by farmers. Asia, a continent with many success stories for aquaculture, leads in farmed production of some catfishes, a diverse group of 37 different families. Globally, the culture of catfishes ranks fifth in global farmed finfish production. Globally, Vietnam leads in the production and export of farmed striped catfish, Pangasianodon hypophthalmus, with 1,400,000 tonnes produced annually from about 7,000 hectares. Similarly, China farmed the non-native Channel catfish, Ictalurus punctatus, into the major crop, with a current annual production of 250,000 tonnes. On the contrary, C. gariepinus, the main farmed catfish species in Africa, records low annual yields, with 240,000 tonnes for the whole continent. This paper explores the factors behind the high production of P. hypophthalmus and I. punctatus in Vietnam and China, respectively, and draws lessons for C. gariepinus farmers in Africa. Specifically, the use of differentiated hatchery and nursery husbandry practices was critical in boosting seed production, quantity, availability, and distribution for expanding the culture of P. hypophthalmus in Vietnam. Improvement of fish species through well-designed genetic improvement programs helped China substantially increase production of I. punctatus. For both species, intensive fish production, as well as the adoption and implementation of suitable policies, increased seed production from hatcheries in both countries. These are discussed as some of the factors that spurred catfish production in the two Asian countries. We argue that if these are adopted by farmers in Africa, they could help improve the production of farmed C. gariepinus on the continent for food and nutrition security as well as generation of livelihood for local communities. [ABSTRACT FROM AUTHOR]

Environmental enrichment has the potential to improve the welfare and post‐release survival of hatchery fish stocked for conservation purposes. However, the effectiveness of environmental enrichment is partly dependent on the fish species, life stage, and specific enrichment structure used. To enhance the effectiveness of environmental enrichment, it is crucial to focus on characteristic differences in enrichment structures, such as type and level. This study investigated how differences in enrichment type and level affected physiological and behavioral aspects of the welfare of pre‐release juvenile rock bream Oplegnathus fasciatus by evaluating growth performance, basal and stressed cortisol levels, antioxidant enzyme activities, and exploratory behaviors regarding anxiety and flexibility. Fish were reared for 4 weeks in different enrichment treatments: barren, low‐level cover structure, high‐level cover structure, low‐level interference structure (LI), and high‐level interference structure (HI). The results revealed that fish reared with the LI treatment showed less anxiety and greater flexibility with respect to exploratory behaviors, without oxidative damage being detected. Despite exhibiting less anxiety as well, fish reared in the HI treatment had oxidative damage, indicated by lower superoxide dismutase activity, compared to those in the barren treatment. In addition, none of these enrichment structures enhanced growth performance or mitigate chronic and acute stress responses. Overall, the low‐level interference structure may be more favorable in promoting the behavioral welfare of the fish. Application of this type and level of enrichment may increase the survival of the hatchery fish after release, which is critical to stocking success. [ABSTRACT FROM AUTHOR]

The whiteleg shrimp Penaeus (Litopenaeus) vannamei is one of the most relevant aquaculture species in Latin America and globally. Among several elements, the improvement of its production depends on the larval genetic quality produced in commercial hatcheries. A strategy for achievement is setting up a longterm management plan that includes the genetic settlement of a breeding population with broad genetic variability and reduced inbreeding levels and the design of adequate management and crossbreeding schemes. The settlement of the breeding population requires a detailed characterization of the genetic composition and diversity of the breeding line(s) that are being managed. The present study evaluated the genetic composition of six wild populations from the southern and northern coasts of the Mexican Pacific (Oaxaca, Guerrero, Nayarit, and Sinaloa) and 56 breeding lots maintained in commercial hatcheries. The genetic profiles of a low-density SNP marker panel (171 and 152 loci for the wild and hatchery-reared groups, respectively) were used to estimate genetic diversity and differentiation within and among samples. The wild population presented significant genetic differences between southern and northern Pacific locations. Although these populations showed higher diversity levels than the cultivated stocks, the genetic pool of the total 56 lots was highly variable with low inbreeding levels. The genetic characteristics of the analyzed populations and cultivated stocks warrant the constitution of a Mexican-origin breeding line with future potential for selection to the environmental conditions of the northwestern region of Mexico. [ABSTRACT FROM AUTHOR]

An investigation was carried out to explore the effect of dietary protein on growth, feed utilization efficiency, condition factor, and lengthweight relationships in common carp (Cyprinus Carpio). 3600 C. carpio were sourced from a Mosul fish hatchery and transported to a private farm in Khanki township, where they were divided into four groups of 900 each. Following a day of acclimation, the fish were placed in 4× 4× 3m water culture ponds and fed diets with different protein concentrations (T1: 30%, T2: 28%, T3: 30%, and T4: 35%) for 90 days. From each group, twenty fish were selected for data collection. Results indicated that the growth parameters, such as daily weight gain, total weight gain, weight gain rate, relative growth rate, metabolic growth rate, and specific growth rate, were higher in fish fed a 28% protein diet (T1) compared to other protein concentrations (T1: 30%, T3: 26%, and T4: 35%). Nutrient utilization parameters, including daily feed consumption, total feed consumption, daily protein consumption, and total protein consumption, were elevated in fish fed with 35% protein (T3). T2 exhibited a significantly higher feed efficiency ratio and protein productive value compared to other diets. The feed conversion ratio was markedly decreased in fish fed a 28% protein diet (T2). Fulton condition factor and modified condition factor were significantly elevated (P< 0.05) with a 28% protein diet (T2), while the relative condition factor decreased. The length-weight relationships indicated isometric growth in T3 (26, 35%), allometric positive growth in T2 (28%), and negative growth in T1 (30%). In conclusion, the study highlighted the superior growth performance and nutrient utilization efficiency in common carp when fed a 28% protein diet (T2). [ABSTRACT FROM AUTHOR]

Saprolegniosis is a major concern in freshwater aquaculture, particularly hatcheries since it causes high mortality and economic losses. Various chemical compounds are used to treat the disease, but they are not recommended due to their hazard effects on fish, humans, and ecosystems. The current study assessed the potential anti-oomycetes activity of crude and aqueous extracts of clove (Syzygium aromaticum) and thyme (Thymus vulgaris) against Saprolegnia australis (S. australis) and Achylia bisexualis (A. bisexualis) in vitro and in vivo. Both herb aqueous stock solutions were eventually prepared using the decoction method. The minimal inhibitory concentrations (MICs) of both herbs' aqueous extracts were determined using the agar plate diffusion method. The ability of both herb aqueous extracts to kill the selected water molds was tested at various time points of exposure. Based on in vitro results, two in vivo field trials were planned to assess the efficacy of crude clove and thyme, first on the fecundity and hatchability of fertilized grass carp eggs. The second trial was designed to assess the antifungal potential against fungal infection during artificial egg incubation. Additionally, two experiments were planned to determine the toxicity parameters of each crude herb in grass carp fingerlings. The second experiment assessed the anti-saprolegniosis activity of selected crude herbs in artificially infected fingerlings. The results showed that S. australis and A. bisexualis were significantly inhibited at a 10% concentration in clove (0.8g/100mL) and thyme (3.2g/100mL) aqueous solutions. However, both herb aqueous extracts had fungicidal properties and killed both fungi at a 50% concentration of their stock solutions (4 and 16g/100mL of clove and thyme, respectively). Incubated eggs exposed to concentrations of 2 and 8g/L clove and thyme, respectively, exhibited high fecundity and hatchability rates. Furthermore, clove and thyme at concentrations of 2 and 4g/L could protect incubated eggs and fry from attack by S. australis and A. bisexualis, respectively. Clove and thyme at concentrations of 0.2-0.25 and 0.5-0.8g/L provided a safe indefinite bath, but at a concentration of 0.5 and 1g/L caused anesthesia after 24 hours of exposure. To successfully treat the infected Ctenopharyngodon idella (C. idella) fingerlings, the most effective doses were 0.25-0.5g/L for clove and 0.5g/L for thyme. Finally, clove and thyme in both crude and aqueous forms could introduce safe, low-cost, environmentally friendly, and easy applications into freshwater hatcheries. [ABSTRACT FROM AUTHOR]

The value of estuaries as nursery habitat for juvenile anadromous salmon is likely variable across estuaries and species. Here, we compiled published empirical data on juvenile salmon estuarine growth and residency. We aimed to quantify the range and variability of these aspects for five species of Pacific salmon across estuaries, methodologies, and life histories. The majority of studies focused on Chinook and coho salmon, largely from their southern range. While there is some evidence of higher growth in wild-origin fish relative to hatchery-origin fish, the wide range of metrics employed made identification of trends among life histories challenging, and unification of reporting could strengthen future research. Different salmon life histories exhibited different residencies, with natural-origin subyearling coho exhibiting the longest mean residency (∼3 months) and 1+ sockeye salmon exhibiting the shortest (3.7 days). Across life histories, hatchery fish exhibited much shorter estuary residencies than wild fish. Collectively, our review highlights key patterns in salmon estuary ecology, identifies knowledge gaps, and lays the foundation for future studies to quantify the importance of estuaries for specific salmon. [ABSTRACT FROM AUTHOR]

With rising environmental temperatures causing concern for the status of freshwater fishes, captive breeding programs may become increasingly important for conservation efforts as well as to support fisheries. Although captive broodstocks provide reliable gamete sources for production stocking, prolonged generations under hatchery conditions can result in changes to fishes as they acclimate to captive settings (domestication) — for example, reduced plasticity due to homogenous captive environments. We assessed the effects of rearing temperature and number of generations spent in captivity on the survival and quality (indicated by lack of malformations) of long-term (F>25) and newly captive (F1) strains of Ontario hatchery brook trout (Salvelinus fontinalis) with shared genetic history. Elevated temperatures decreased likelihood of survival between the pre-exogenous feed and emergent fry stages and had a greater impact on fry quality (rate of malformations) on F1 fish compared with F>25 fish, suggesting no reduction in plasticity due to prolonged captivity. However, overall survival between F1 and F>25 fish was not different. The combined effects of elevated rearing temperatures and number of hatchery generations suggest that (selection) changes due to captivity can occur rapidly even under benign conditions and that additive stressor effects of captivity and temperature have the potential to impact newly established strains. [ABSTRACT FROM AUTHOR]

Agua Hedionda Lagoon (AHL), a tidal estuary located on the southern California coast, supports a diverse ecosystem while serving numerous recreation activities, a marine fish hatchery, a shellfish hatchery, and the largest desalination plant in the western hemisphere. In this work, a 1-year time series of carbon dioxide data is used to establish baseline average dissolved inorganic carbon conditions in AHL. Based on a mass balance model of the outer basin of the lagoon, we propose that AHL is a source of inorganic carbon to the adjacent ocean, through advective export, at a rate of 5.9 × 106 mol C year−1, and a source of CO2 to the atmosphere of 0.21 × 106 mol C year−1 (1 mol C m−2 year−1), implying a net heterotrophic system on the order of 6.0 × 106 mol C year−1 (30 mol C m−2 year−1). Although variable with a range throughout the year of 80% about the mean, the ecosystem remained persistently heterotrophic, reaching peak rates during the summer season. Using results from the mass balance, the annual cycle of selected properties of the aqueous CO2 system (pH, pCO2, and CaCO3 saturation state) were mathematically decomposed in order to examine the relative contribution of drivers including advection, ecosystem metabolism, and temperature that act to balance their observed annual cycle. Important findings of this study include the identification of advection as a prime driver of biogeochemical variability and the establishment of a data-based estimate of mean flushing time for AHL. [ABSTRACT FROM AUTHOR]

Assessing habitat quality is a major goal of conservationists and restoration practitioners, but to associate habitat quality with biomarkers of vagile animals, the biomarkers must respond rapidly. Here, we identified a biomarker capable of rapidly detecting food limitation in the imperiled Delta Smelt (Hypomesus transpacificus), a pelagic fish endemic to the San Francisco Estuary (SFE). We conducted an experiment with fed and unfed treatments of hatchery-raised, sub-adult Delta Smelt that were sampled at 12 time points: 0, 1, 2, 3, 4, 5, 6, 7, 9, 11, 14, and 21 days. We then compared four biomarkers using Day 21 fish: RNA/DNA in liver, triglycerides in liver, glycogen in liver, and glycogen in muscle. Of the liver endpoints, glycogen had the largest difference between treatments at Day 21, so we compared it to muscle glycogen across all time points. Liver glycogen declined by 60% after 1 day of fasting and remained depressed in the fasting treatment across all subsequent time points. Muscle glycogen also responded rapidly, taking only 2 days to decline by 39% in the fasting treatment, but the difference was inconsistent across subsequent time points. When applied to hatchery-released Delta Smelt collected from the SFE, liver glycogen concentrations were less than half that of the fed hatchery fish, consistent with the hypothesis of food limitation in the wild, but also several other potential causes. This study highlights the utility of liver glycogen as an indicator of recent foraging success in Delta Smelt. [ABSTRACT FROM AUTHOR]

This article discusses the significance of water contaminant testing in amphibian reintroduction programs. It emphasizes that the health of released amphibians and the quality of their reintroduction habitat are crucial for their survival. The article suggests measuring contaminants in site water or conducting ex situ exposures to identify toxic levels of human-made contaminants and predict amphibian survival. It also highlights the negative effects of chemical pollution on amphibians and recommends avoiding reintroduction sites with high concentrations of chemical contaminants. The article concludes by recommending steps to enhance the effectiveness of amphibian reintroduction programs, such as assessing contaminant risks and exposing captive-bred offspring to site water before release. It provides guidelines for managers and supporters of amphibian captive breeding programs and reintroductions. [Extracted from the article]

Background: Restocking by introducing hatchery-reared fish into wild habitats aids in the restoration of fishery aquatic ecosystems and reefs to increase the abundance of fish resources, restore the ecological balance of water bodies, and enhance ecosystem functioning. Accurately, rapidly, and effectively evaluating the success of restocking using chemical markers (e.g., strontium [Sr]) remains challenging for fisheries management. Consequently, for non-lethal fish sampling, hard tissues, such as fin rays, have received increasing attention as a target for marking method. However, data on the differences in marking different types of fin rays remain limited. Therefore, we exposed juvenile blunt snout bream individuals (Megalobrama amblycephala) to 0 (control group) or 800 mg/L of SrCl2·6H2O (marked group) for 5 days and transferred them into normal aerated water for post-immersion culture. We sampled their pectoral, dorsal, ventral, anal, and caudal fin rays. The Sr marks among the fin types were sampled at 0 and 20 days post-immersion and evaluated using an electron probe micro-analyzer (EPMA) for the five-day Sr/Ca ratios, along with line transect and Sr mapping analyses. Results: Sr marking signatures were observed in all fin types in the marked group, with a success rate of up to 100%. Although marking efficiency varied among the different fin ray types, the highest Sr/Ca ratios were most often detected in the dorsal fin. Cross-sectional Sr concentration maps of all fin rays sampled showed high-Sr domains in the marked group; in contrast, the entire cross-sections of the control group displayed low Sr contents, indicating successful marking efficiency. Conclusions: Fin ray Sr marking is a successful method for juvenile M. amblycephala, with the advantages of non-lethality and negligible sampling injuries, facilitating the rapid and effective evaluation of Sr marking in restocking M. amblycephala. [ABSTRACT FROM AUTHOR]

Flavobacterium psychrophilum, the causative agent of bacterial coldwater disease, causes substantial economic losses in salmonid farms and hatcheries. Some multilocus sequence types (ST) of F. psychrophilum are more likely to be associated with fish farms and hatcheries, but it is unclear if these patterns of association represent genetic lineages that are more adapted to aquaculture environments. Towards elucidating the disease ecology of F. psychrophilum, the culturability of 10 distinct F. psychrophilum STs was evaluated for 13 weeks in three microcosms including sterilized well water, sterilized well water with commercial trout feed, or sterilized well water with raceway detritus. All STs remained culturable in each of the microcosms for at least 8 weeks, with bacterial concentrations often highest in the presence of raceway detritus. In addition, most (e.g., 90%) STs remained culturable for at least 13‐weeks. Significant differences in log10 cfus were observed among STs, both within and between microcosms, suggesting potential variability in environmental persistence capacity among specific variants. Collectively, results highlight the ability of F. psychrophilum to not only persist for weeks under nutrient‐limited conditions but also thrive in the presence of organic substrates common in fish farms and hatchery‐rearing units. [ABSTRACT FROM AUTHOR]

Fish hatcheries are widely used to enhance fisheries and supplement declining wild populations. However, substantial evidence suggests that hatchery fish are subject to differential selection pressures compared to their wild counterparts. Domestication selection, or adaptation to the hatchery environment, poses a risk to wild populations if traits specific to success in the hatchery environment have a genetic component and there is subsequent introgression between hatchery and wild fish. Few studies have investigated domestication selection in hatcheries on a genomic level, and even fewer have done so in parallel across multiple hatchery–wild population pairs. In this study, we used low‐coverage whole‐genome sequencing to investigate signals of domestication selection in three separate hatchery populations of Chinook salmon, Oncorhynchus tshawytscha, after approximately seven generations of divergence from their corresponding wild progenitor populations. We sequenced 192 individuals from populations across Southeast Alaska and estimated genotype likelihoods at over six million loci. We discovered a total of 14 outlier peaks displaying high genetic differentiation (FST) between hatchery–wild pairs, although no peaks were shared across the three comparisons. Peaks were small (53 kb on average) and often displayed elevated absolute genetic divergence (Dxy) and linkage disequilibrium, suggesting some level of domestication selection has occurred. Our study provides evidence that domestication selection can lead to genetic differences between hatchery and wild populations in only a few generations. Additionally, our data suggest that population‐specific adaptation to hatchery environments likely occurs through different genetic pathways, even for populations with similar standing genetic variation. These results highlight the need to collect paired genotype–phenotype data to understand how domestication may be affecting fitness and to identify potential management practices that may mitigate genetic risks despite multiple pathways of domestication. [ABSTRACT FROM AUTHOR]

Evaluating salmon hatchery supplementation programs requires assessing not only program objectives but identifying potential risks to wild populations as well. Such evaluations can be hampered by difficulty in distinguishing between hatchery‐ and wild‐born returning adults. Here, we conducted 3 years (2011–2013) of experimental hatchery supplementation of sockeye salmon in Auke Lake, Juneau, Alaska where a permanent weir allows sampling and genotyping of every returning adult (2008–2019). We identified both hatchery‐ and wild‐born returning adults with parentage assignment, quantified the productivity (adult offspring/spawner) of hatchery spawners relative to that of wild spawners, and compared run timing, age, and size at age between hatchery‐ and wild‐born adults. Hatchery‐spawning females produced from approximately six to 50 times more returning adults than did naturally spawning females. Supplementation had no discernable effect on run timing and limited consequences for size at age, but we observed a distinct shift to younger age at maturity in the hatchery‐born individuals in all three brood years. The shift appeared to be driven by hatchery‐born fish being more likely to emigrate after one, rather than two, years in the lake but the cause is unknown. In cases when spawning or incubation habitat is limiting sockeye salmon production, hatchery supplementation can be effective for enhancing the number of returning adult fish but not without the risk of phenotypic change in the recipient population, which can be an undesired outcome of hatchery supplementation. This study adds to a growing body of evidence suggesting that phenotypic change within a single generation of captive spawning might be widespread in salmon hatchery programs. [ABSTRACT FROM AUTHOR]

Coregonines (ciscoes and whitefishes) are economically, ecologically, and culturally important fishes that are distributed throughout the Northern Hemisphere. In the Laurentian Great Lakes, coregonines declined throughout the 19th and 20th centuries, and managers have prioritized their restoration. A key restoration tool is reintroduction via stocking. However, hatchery‐reared coregonines can display different morphologies than wild fish, which could affect their fitness. Unfortunately, our understanding of these differences is limited because previous work did not adequately remove allometric effects in morphological analyses. We compared morphologies between wild and hatchery‐reared Bloater (Coregonus hoyi) from the same stock using appropriate size corrections. Hatchery‐reared fish had shorter heads, shorter dorsal fins, and shallower bodies than wild fish. Moreover, some characters differed across wild fish collections. Our results improve our understanding of how artificial rearing can impact coregonine morphology, and we recommend future studies on what causes these differences and whether they impact fitness. [ABSTRACT FROM AUTHOR]

Objective: Hatchery‐produced salmon and steelhead Oncorhynchus mykiss mitigate for habitat loss and support valuable commercial, recreational, and tribal fisheries. However, excessive interactions between hatchery and wild fish can also cause harm to wild populations. Weirs have been implemented as a management tool to remove returning hatchery‐origin Chinook Salmon O. tshawytcha adults to reduce the proportion of hatchery‐origin spawners (pHOS) in spawning areas used by their wild counterparts. Using a decade of data since new weirs were implemented, our objective was to evaluate the efficacy of this management approach. Methods: Weirs were installed in six tributaries of the lower Columbia River, Washington. Using data from both weir operations and spawning ground surveys, we quantified weir efficiency (the proportion of upstream migrants captured by the weir) and resultant pHOS in wild spawning areas and evaluated evidence for unintended effects of weirs on naturally spawning salmon in years with (2011–2017) and without weirs (2002–2010) in one population by evaluating weir effects on spawner apparent residence time, distribution, and recruitment to the juvenile stage. Result: Weir efficiencies were highly variable across years and locations (7.3–100.0%). Estimates of pHOS were variable among populations and years (interannual population mean range: 11.9% to 75.2%) but were higher in all but 2 of the 43 population‐year combinations than needed to maintain recovery‐plan‐targeted levels of population viability using quantitative genetic model‐based standards identified by the Hatchery Scientific Review Group. Several factors contributed to the proportion of hatchery spawners exceeding pHOS standards at the population level, including fish passing weirs during freshets, spawning below weir sites and in tributaries without weirs, and imperfect marking of hatchery‐released juveniles. In the sole watershed with sufficient pre‐weir data to evaluate before–after changes, we documented a downstream shift in the spatial distribution of redds, lower apparent residence time of spawners, and lower production of parr in years following weir installation. Conclusion: Our results indicate that using weirs as a tool to reduce hatchery–wild interactions on the spawning grounds is challenging. Weir implementation reduced pHOS; however, in most cases, resulting pHOS was not low enough to facilitate fit and viable wild populations. Weirs also were associated with unintended negative impacts to the single population where we had adequate before and after weir implementation data to evaluate effects. These impacts may be harmful to recovery efforts and offset the intended benefits of weirs to wild populations. Our study highlights the need for adaptive management to realize the goals intended for weirs, underscores the need for experimental design approaches, and identifies opportunities for future work. Impact statementWeirs demonstrated limited efficacy in removing hatchery fall Chinook Salmon from wild spawning areas and were associated with negative impacts on spawner distribution and productivity, raising the possibility that alternative approaches will be needed to reduce the effects of hatcheries on wild populations. [ABSTRACT FROM AUTHOR]

The economic impact of skeletal anomalies in aquaculture farming is a significant issue for the industry, as deformed fish are frequently discarded because of their low survival rate and a variety of other disadvantages, including increased costs, consumer distrust of aquaculture products, and ethical concerns. The goal of this article is to propose a method for calculating the direct costs of severe skeletal anomalies in typical Mediterranean seabream and seabass aquaculture hatcheries using a deterministic static model programmed in MATLAB that simulates their annual operation. Our findings suggest that larger hatcheries experience higher direct costs associated with severe skeletal anomalies but have better financial stability and significantly higher expected profits. Mean results indicate that the annual economic losses of severe skeletal anomalies for seabream and seabass Mediterranean aquaculture are 22.88 million euros per year for a scenario of low severe skeletal anomalies, 65.34 million euros per year for a scenario of medium severe skeletal anomalies, and 115.98 million euros per year for a scenario of high severe skeletal anomalies. Furthermore, some options for increasing the financial stability of the hatcheries are to increase the sale price of fingerlings, reduce the feed conversion ratio, and reduce the feed unit cost. [ABSTRACT FROM AUTHOR]

A field study comparing two vaccine regimes against pancreas disease (PD) was carried out in 2018 S0 year class smolts at two commercial sea cage sites in southern Norway. The fish from the same hatchery source were immunized using licensed vaccines; either a DNA PD vaccine and a hexavalent oil‐adjuvanted vaccine (group A), or a heptavalent oil‐adjuvanted PD vaccine (group B). The experimental design included the two fish groups reared together (15% as group A and 85% as group B) in four large hatchery tanks. These fish groups were later transferred to four production cages at two separate sea sites (two cages per site). In the absence of any notable PD prior to the pre‐harvest sampling, the primary objective and outcome variables entailed evaluation of vaccine side effects and their impact on growth. The results show that vaccine and sea cage site significantly impacted prevalence and severity of a newly described pathology named cross‐stitch vertebrae. Further, moderate to severe cross‐stitch pathology (scores ≥3) resulted in significantly reduced growth. [ABSTRACT FROM AUTHOR]

In Japan, the release of high-quality hatchery-reared juvenile fish is intended to mitigate against recent declines in adult returns of chum salmon Oncorhynchus keta. One approach to accomplish this aim is through oral supplementation with functional ingredients prior to release of the juveniles. This study aimed to clarify the effect of docosahexaenoic acid (DHA), a marine-derived n-3 polyunsaturated fatty acid (PUFA), on the neural function of juvenile salmon. We examined the messenger RNA (mRNA) expression of synaptosome-associated protein 25 (SNAP25), a molecule related to synaptic vesicle endocytosis, in the brain of hatchery-reared chum salmon juveniles whose feed was supplemented with a DHA-enriched oil for a short period of time. In addition, we tested critical swimming speed to clarify the effect of this supplementation on swimming ability. snap25b expression in the rostral and mid parts of brain was higher in the PUFA-supplemented fish than in the control groups. Both snap25a expression in the mid and caudal parts of brain, including the motor centers, and the results of the swimming ability test were higher in the n-3 PUFA-supplemented group. These findings suggest that short-term oral DHA supplementation in juvenile chum salmon via commercial salmon feed contributes to the enhancement of synaptic plasticity in the central nervous system. [ABSTRACT FROM AUTHOR]

Multiple evolutionary processes influence genome‐wide allele frequencies and quantifying effects of genetic drift, and multiple forms of selection remain challenging in natural populations. Here, we investigate variation at major effect loci in contrast to patterns of neutral drift across a wide collection of steelhead (Oncorhynchus mykiss) populations that have declined in abundance due to anthropogenic impacts. Whole‐genome resequencing of 74 populations of steelhead revealed genome‐wide patterns (~8 million SNPs) consistent with expected neutral population structure. However, allelic variation at major effect loci associated with adult migration timing (chromosome 28: GREB1L/ROCK1) and age at maturity (chromosome 25: SIX6) reflected how selection has acted on phenotypic variation in contrast with neutral structure. Variation at major effect loci was influenced by evolutionary processes with differing signals between the strongly divergent Coastal and Inland lineages, while allele frequencies within and among populations within the Inland lineage have been driven by local natural selection as well as recent anthropogenic influences. Recent anthropogenic effects appeared to have influenced the frequency of major effect alleles including artificial selection for specific traits in hatchery stocks with subsequent gene flow into natural populations. Selection from environmental factors at various scales has also likely influenced variation for major effect alleles. These results reveal evolutionary mechanisms that influence allele frequencies at major effect loci that are critical for conservation of phenotypic traits and life history variation of this protected species. [ABSTRACT FROM AUTHOR]