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Identifying the scale of population processes is important for sustainable fisheries management. In the North Sea, the lesser sandeel, Ammodytes marinus, is now managed as seven stocks delineated on the basis of biophysical model predictions of the limited scale of larval mixing. This study used otolith chemistry to evaluate whether the stock units defined from these predictions actually reflect the degree of isolation of early life stages. Elemental composition near the core, settlement check and summer opaque zone were examined using laser ablation-inductively coupled plasma mass spectrometry in young of the year, sampled across 8 grounds within three of the main fished stocks in 2011. There were significant spatial differences in otolith chemistry enabling post-settled juveniles to be discriminated among stock areas and even between some grounds. Clustering of near core chemistry pointed to four natal sources, with dominant clusters in each of the three stocks studied and one unique to the Central Western North Sea (sandeel assessment area 4). Moreover, near core chemistry was similar to that of post-settled juveniles at the stock area level. Consistency in the scaling of early life mixing predicted by biophysical models and otolith chemistry supports the present stock units used in assessments. [ABSTRACT FROM AUTHOR]

Technological advances have led to smaller transmitters for telemetry studies involving small fishes, including juveniles, which minimize effects on fish performance and retention caused by tag burden. We evaluated three transmitter application procedures (external attachment and internal implantation with and without a trailing antenna) on the growth, survival, and tag retention of juvenile least cisco Coregonus sardinella over a 60-day laboratory experiment. For fish that received internal transmitters, we also examined the effects of suture type (absorbable versus non-absorbable) and suture knot adhesive (use versus non-use of 3M™ Vetbond™). In general, there were minimal to no effects of suture type or the use/non-use of knot adhesive on fish performance. Only least cisco in the control (no transmitter) and external transmitter groups exhibited positive growth over the experimental period. Despite growth differences among treatments, there were no significant differences in final mean total length and wet weight among treatment groups. Least cisco with internal transmitters exhibited significantly lower survival (trailing antenna: range, 53–73%; no trailing antenna: 80%) than fish in control (100%) and external transmitter (93%) groups. External transmitters were not shed by juvenile least cisco; however, transmitter shed rate ranged from 0% to 33% for fish in internal implant treatments. Our results showed that externally attached transmitters had a lower impact on fish growth, mortality, and tag retention than internal implants, which is an important consideration for telemetry evaluations involving fish that are susceptible to handling stress such as juvenile least cisco. [ABSTRACT FROM AUTHOR]

Distribution shifts of demersal fishes are important adaptive responses to warming oceans for species' persistence. Shifts are facilitated by factors such as adult movement and dispersal of pelagic larvae to normally cooler regions, where increasing ocean temperatures are now enhancing larval and juvenile survival. However, successful recruitment (i.e. larval settlement) at these new regions can be constrained by resource availability, specialisation (food, habitat) and ecological interactions (competition, predation). Evaluating the capacity or likelihood of a species to successfully shift or expand its range, provides information relevant to biodiversity conservation and fisheries management, and is particularly important for species with restricted ranges. Choerodon rubescens (Günther, 1862) is an exploited labrid endemic to ~ 1400 km of the west Australian coastline, encompassing 13° of latitude and a 6°C temperature gradient. This region recently experienced a rapid warming event of ~ 3°C, which lasted 3 months and mirrored ocean temperatures expected in the next 50 years. Following this event, high levels of recruitment of C . rubescens occurred towards its southern, cooler distribution limit. Juvenile abundances were surveyed in this study to evaluate: (1) the effect of elevated temperatures on recruitment success across shallow water habitats spanning the species' distribution, (2) temporal variation in recruitment success in the typically cooler, southern part of its range and (3) ecological characteristics important to recruit survival, including habitat preferences, diet and behaviour. Juvenile C . rubescens were significantly more abundant at the margin between reef and sand and towards the cooler southern range end. Reef margin habitat provides access to shelter from predators within the reef and to sand-associated invertebrate prey in adjacent soft sediments, where most feeding activity occurred. Juveniles were abundant (0.3 to 4 fish/40 m 2 ) in reef margin habitats of the southern cooler region for three consecutive years, with individuals represented by multiple cohorts, indicating suitable environmental conditions for ongoing recruitment and survival. Juveniles at this habitat were able to compete effectively with other co-occurring labrids for invertebrate prey. As oceans warm, the number of recruits arriving and surviving beyond the existing cooler range limit will be dependent on factors such as successful spawning, larval delivery and survival, and availability of reef margin habitat with associated prey; these factors will determine the successful range shift or expansion of C . rubescens . We present an example of how range-wide spatiotemporal ecological studies of juvenile fish can identify range shift capacity and inform management adaptive to climate change. [ABSTRACT FROM AUTHOR]

This study compared the bioaccumulation of anthropogenic nuclides ( 65 Zn, 134 Cs, 60 Co and 241 Am) between the egg and juvenile life stages of a small shark ( Scyliorhinus canicula ), based on previously published experimental data. Rates of accumulation over 15 days were derived and summed for the transfer pathways which were specific to these two life stages. Radionuclide transfers to the egg and its embryo & yolk were quantified for i) the maternal pathway following her uptake of radionuclides via food and seawater and ii) from seawater following its oviposition. For the juvenile, the transfer of radionuclides were measured for aqueous & dietary pathways. The results show that, compared to juveniles, eggs have equivalent rates of accumulation of 65 Zn and 134 Cs but enhanced accumulation of 241 Am by a factor of five and of 60 Co by two orders of magnitude. The radiological exposure of the embryo due to radionuclides maternally transferred to the embryo & yolk is also enhanced for the alpha-emitting 241 Am. This enhanced accumulation of 241 Am and 60 Co, as well as the equivalent accumulation of 65 Zn and 134 Cs, suggest greater likely vulnerability to radiation damage in eggs as compared to juveniles. Radiological dose assessment confirmed highest doses to the egg which is predominantly due to accumulated 241 Am. [ABSTRACT FROM AUTHOR]

Coastal nursery habitats are essential for the renewal of adult fish populations. We quantified the availability of a coastal nursery habitat (shallow heterogeneous rocky bottoms) and the spatial variability of its juvenile fish populations along 250 km of the Catalan coastline (France and Spain). Nurseries were present in 27% of the coastline, but only 2% of them benefited from strict protection status. For nine taxa characteristic of this habitat, total juvenile densities varied significantly between nursery sites along the coastline, with the highest densities being found on the northern sites. Recruitment level (i.e. a proxy of nursery value) was not explained by protection level, but it was moderately and positively correlated with an anthropization index. Patterns of spatial variations were taxa-specific. Exceptional observations of four juveniles of the protected grouper Epinephelus marginatus were recorded. Our data on habitat availability and recruitment levels provides important informations which help to focus MPA management efforts. [ABSTRACT FROM AUTHOR]

In response to a lack of data supporting (or otherwise) legally mandated escape gaps in an Australian recreational trap fishery for eastern rock lobster, Sagmariasus verreauxi , the effects of all prescribed options on catches were investigated. Round traps without escape gaps (control) were compared against those with either one (57 × 500 mm), two (both 57 × 250 mm) or three (all 57 × 200 mm) rectangular openings (i.e. all similar areas) evenly located around the base of the trap perimeter. All traps with escape gaps retained significantly fewer undersized (by 54–84%) but more legal-sized (by 1.6–2.8 times) S. verreauxi than the control. Irrespective of escape gaps, there was also a positive association between antennae loss by S. verreauxi and trap soak time, although only one undersized individual died (for a total associated discard mortality <2%). These observations are explained by possible density-dependant behavioural responses of trapped S. verreauxi , with legal-sized individuals replacing escaping juveniles and increased physical interactions among all catches the longer they remained in traps. Escape gaps could be promoted in the fishery, not only for their utility in reducing catches of undersized individuals, but via the potential for almost triple the fishing power for targeted catches. [ABSTRACT FROM AUTHOR]

Two diets with the same docosahexaenoic acid:eicosapentaenoic acid ratio (1.8:1), but with different n -3 long-chain polyunsaturated fatty acid ( n - 3 LC-PUFA) contents [29.5 g/kg (DH) and 17.9 g/kg (DL)], were designed and fed to two groups of 46 female and 30 male Siberian sturgeon ( Acipenser baerii ) broodstock for 11 months. Sperm and egg quality and reproductive performance indices were recorded during cross-breeding. Larval offspring resulting from cross-matings were divided into the following four groups for a 30-d feeding trial: D1 ( DH ♀ × DH ♂), D2 ( DH ♀ × DL ♂), D3 ( DL ♀ × DH ♂), and D4 ( DL ♀ × DL ♂). The results showed that egg size of the DH group was significantly larger than that of the DL group. With respect to sperm quality, there were no significant differences in wobble, amplitude of lateral head displacement, beat/cross frequency, and mean angular displacement between the two dietary groups; however, a high n -3 LC-PUFA diet increased sperm curvilinear, straight-line, and average path velocities in the DH group. The DH group had significantly lower levels of serum triglyceride, low-density lipoprotein cholesterol, and malonaldehyde, but higher superoxide dismutase level, and total antioxidant capacity compared with the DL group. At 7 and 32 days post hatching, the survival of larvae in groups D1 and D2 was significantly higher than that in groups D3 and D4. The specific growth rate of larvae in group D4 was the lowest among the four groups. The results suggest that n -3 LC-PUFA can improve the reproductive performance of male and female broodstock of Siberian sturgeon and the quality of their offspring, but that n -3 LC-PUFA enrichment of the diet is more critical for female broodstock than for males. [ABSTRACT FROM AUTHOR]

The nutritional value of whole wheat, corn, rye and barley was evaluated for European sea bass. Four isoproteic and isolipidic diets containg 30% of each whole cereal meal were formulated. A growth trial and a digestibility trial were conducted and fish performance was evaluated in terms of growth, feed intake, feed utilization, macronutrients digestibility, liver composition, glycaemia and cholesterolemia levels and gut histomorphology. Growth and feed utilization ranged from 1.43 to 1.46 and from 0.55 to 0.58, respectively, and were similar among experimental groups. Whole body and liver composition, hepatosomatic and visceral indexes were also not affected by dietary composition. Corn diet revealed the lower dry matter (62.9) and starch (55.5) apparent digestibility coefficients. Protein digestibility in fish fed the rye diet was the lowest of all groups (91.3) and differed from that of wheat diet group (93.2), which might be due to antinutritional factors present in this feedstuff. Plasmatic glucose levels suggested a slower absorption rate in fish fed barley and corn diets. No signs of enteropathy related to the whole cereal meals were observed. Among cereals tested, rye seemed to be the less tolerated by sea bass, although all diets were well accepted and sea bass performed equally well with all diets. [ABSTRACT FROM AUTHOR]

Recent studies reported positive effects of taurine supplementation to plant protein-based diets on fish growth performance and feed conversion ratio but the mechanisms involved remain unclear. The objective of this work was to provide a first insight on the importance of taurine on dietary protein and lipid absorption and utilisation, in Senegalese sole ( Solea senegalensis ) juveniles fed plant-based diets. Seven practical diets were tested: a fishmeal-based diet (FM) and a plant protein-based formula (PP85) to which taurine was added in graded levels: 0.2% (TAU1), 0.3% (TAU2), 0.4% (TAU3), 0.7% (TAU4) and 1.5% (TAU5). Short-term metabolic trials were performed by tube-feeding the different experimental diets labelled with different tracers: 14 C-taurine, 14 C-triolein (as tracer of dietary triacylglycerol) and a mixture of 14 C-amino acids. Feeding sole juveniles with the PP85 diet affected taurine metabolism, since a higher proportion of dietary taurine was directed to gallbladder and probably used for bile salt synthesis. Consistent with this, fish receiving the plant-based low taurine-content diets (PP85 and TAU1) displayed a poor triacyglycerol digestion capacity. A higher proportion of 14 C-amino acids was retained in fish muscle when fed the TAU5 compared to the PP85 diet. These short-term trials suggested that taurine supplementation to a plant-based diet might be beneficial to sole performance by enhancing bile salt synthesis and triacylglycerol digestion as well as muscle amino acid retention. However, this dietary supplementation should be tested in long-term trials to verify the effect on fish growth and to assess the beneficial effects on protein and lipid metabolism suggested here. Statement of relevance in the general field of aquaculture (limited to 60 characters) Adding taurine to a plant-based diet is beneficial for sole [ABSTRACT FROM AUTHOR]

Based on the concept of nutritional programming in mammals, we tested whether a short term hyper or hypo vitamin stimulus during first-feeding could induce long-lasting changes in nutrient metabolism in rainbow trout. Trout alevins received during the 4 first weeks of exogenous feeding a diet either without supplemental vitamins (NOSUP), a diet supplemented with a vitamin premix to satisfy the minimal requirement in all the vitamins (NRC) or a diet with a vitamin premix corresponding to an optimal vitamin nutrition (OVN). Following a common rearing period on the control diet, all three groups were then evaluated in terms of metabolic marker gene expressions at the end of the feeding period (day 119). Whereas no gene modifications for proteins involved in energy and lipid metabolism were observed in whole alevins (short-term effect), some of these genes showed a long-term molecular adaptation in the muscle of juveniles (long-term effect). Indeed, muscle of juveniles subjected at an early feeding of the OVN diet displayed up-regulated expression of markers of lipid catabolism (3-hydroxyacyl-CoA dehydrogenase – HOAD - enzyme) and mitochondrial energy metabolism (Citrate synthase - cs , Ubiquitinol cytochrome c reductase core protein 2 - QCR2, cytochrome oxidase 4 - COX4, ATP synthase form 5 - ATP5A) compared to fish fed the NOSUP diet. Moreover, some key enzymes involved in glucose catabolism (Muscle Pyruvate kinase - PKM) and amino acid catabolism (Glutamate dehydrogenase - GDH3) were also up regulated in muscle of juvenile fish fed with the OVN diet at first-feeding compared to fish fed the NOSUP diet. We researched if these permanently modified gene expressions could be related to global modifications of epigenetic marks (global DNA methylation and global histone acetylation and methylation). There was no variation of the epigenetic marks in muscle. However, we found changes in hepatic DNA methylation, global H3 acetylation and H3K4 methylation, dependent on the vitamin intake at early life. In summary, our data show, for the first time in fish, that a short-term vitamin-stimulus during early life may durably influence muscle energy and lipid metabolism as well as some hepatic epigenetic marks in rainbow trout. Statement of relevance Programming at first feeding with different levels of vitamins was successfully tested in fish for the first time. These data proove one more time the importance of the early life on the fish metabolism in adults. [ABSTRACT FROM AUTHOR]

A trial was carried out with gilthead seabream juveniles, aiming to investigate the ability of an enhanced dietary formulation (diet Winter Feed, WF, containing a higher proportion of marine-derived protein sources and supplemented in phospholipids, vitamin C, vitamin E and taurine) to assist fish in coping with winter thermal stress, compared to a low-cost commercial diet (diet CTRL). In order to identify the metabolic pathways affected by WF diet, a comparative two dimensional differential in-gel electrophoresis (2D-DIGE) analysis of fish liver proteome (pH 4–7) was undertaken at the end of winter. A total of 404 protein spots, out of 1637 detected, were differentially expressed between the two groups of fish. Mass spectrometry analysis of selected spots suggested that WF diet improved oxidative stress defense, reduced endoplasmic reticulum stress, enhanced metabolic flux through methionine cycle and phenylalanine/tyrosine catabolism, and induced higher aerobic metabolism and gluconeogenesis. Results support the notion that WF diet had a positive effect on fish nutritional state by partially counteracting the effect of thermal stress and underlined the sensitivity of proteome data for nutritional and metabolic profiling purposes. Intragroup variability and co-measured information were also used to pinpoint which proteins displayed a stronger relation with fish nutritional state. Significance Winter low water temperature is a critical factor for gilthead seabream farming in the Mediterranean region, leading to a reduction of feed intake, which often results in metabolic and immunological disorders and stagnation of growth performances. In a recent trial, we investigated the ability of an enhanced dietary formulation (diet WF) to assist gilthead seabream in coping with winter thermal stress, compared to a standard commercial diet (diet CTRL). Within this context, in the present work, we identified metabolic processes that are involved in the stress-mitigating effect observed with diet WF, by undertaking a comparative analysis of fish liver proteome at the end of winter. This study brings information relative to biological processes that are involved in gilthead seabream winter thermal stress and shows that these can be mitigated through a nutritional strategy, assisting gilthead seabream to deal better with winter thermal conditions. Furthermore, the results show that proteomic information not only clearly distinguishes the two dietary groups from each other, but also captures heterogeneities that reflect intra-group differences in nutritional state. This was exploited in this work to refine the variable selection strategy so that protein spots displaying a stronger correlation with “nutritional state” could be identified as possible indicators of gilthead seabream metabolic and nutritional state. Finally, this study shows that gel-based proteomics seems to provide more reliable information than transmissive FT-IR spectroscopy, for the purposes of nutritional and metabolic profiling. [ABSTRACT FROM AUTHOR]

Grass carp ( Ctenopharyngodon idella ) is one of the most important species in China. Decabromodiphenyl ethane (DBDPE) is a brominated flame retardant that has been used widely in industry, and has been observed to accumulate in the tissues of fish from South China. Evidence has shown that DBDPE is toxic to aquatic animals, but the molecular response has been unclear. MicroRNAs (miRNAs) are small noncoding and negative regulatory RNAs that are 20–24 nucleotides in length, which are involved in a wide range of biological processes. We took advantage of deep-sequencing techniques to accurately and comprehensively profile the kidney miRNA expression of grass carp after 8 weeks of oral exposure to DBDPE. After mapping sequencing data to the genome and Expressed Sequence Tags (ESTs) of grass carp, we identified 493 miRNAs in the sequenced grass carp samples, which included 51 new miRNAs. The results indicated that 5 miRNAs were significantly down-regulated and 36 miRNAs were significantly up-regulated (FDR < 0.001, 1.5-fold change) after DBDPE exposure. Real-time quantitative PCR (RT-qPCR) was performed on 4 miRNAs from the two samples, and the sequencing and RT-qPCR data were consistent. This study provides the first comprehensive identification of grass carp miRNAs, and the first expression analysis of grass carp miRNAs following DBDPE exposure. The results indicated that miRNAs have potential for use as biomarkers. [ABSTRACT FROM AUTHOR]

Dissolved copper is one of the more pervasive and toxic constituents of stormwater runoff and is commonly found in stream, estuary, and coastal marine habitats of juvenile salmon. While stormwater runoff does not usually carry copper concentrations high enough to result in acute lethality, they are of concern because sublethal concentrations of copper exposure have been shown to both impair olfactory function and alter behavior in various species in freshwater. To compare these results to other environments that salmon are likely to encounter, experiments were conducted to evaluate the effects of salinity on the impairment of olfactory function and avoidance of copper. Copper concentrations well within the range of those found in urban watersheds, have been shown to diminish or eliminate the olfactory response to the amino acid, l -serine in freshwater using electro-olfactogram (EOG) techniques. The olfactory responses of both freshwater-phase and seawater-phase coho and seawater-phase Chinook salmon, were tested in freshwater or seawater, depending on phase, and freshwater-phase coho at an intermediate salinity of 10‰. Both 10‰ salinity and full strength seawater protected against the effects of 50 μg copper/L. In addition to impairing olfactory response, copper has also been shown to alter salmon behavior by causing an avoidance response. To determine whether copper will cause avoidance behavior at different salinities, experiments were conducted using a multi-chambered experimental tank. The circular tank was divided into six segments by water currents so that copper could be contained within one segment yet fish could move freely between them. The presence of individual fish in each of the segments was counted before and after introduction of dissolved copper (<20 μg/L) to one of the segments in both freshwater and seawater. To address whether use of preferred habitat is altered by the presence of copper, experiments were also conducted with a submerged structural element. The presence of sub-lethal levels of dissolved copper altered the behavior of juvenile Chinook salmon by inducing an avoidance response in both freshwater and seawater. While increased salinity is protective against loss of olfactory function from dissolved copper, avoidance could potentially affect behaviors beneficial to growth, survival and reproductive success. [ABSTRACT FROM AUTHOR]

According to the nursery size hypothesis, flatfish recruitment is constrained by nursery area. Thus, if resource selection models can be shown to accurately predict the location and geographic extent of flatfish nursery areas, they will become important tools in the management and study of flatfish population dynamics. We demonstrate that some resource selection models derived previously to predict the presence and absence of juvenile flatfishes near shore were applicable to the broader continental shelf. For other age-species groups, derivation of new models for the continental shelf was necessary. Our study was conducted in the western Gulf of Alaska (GoA) during October 2011 on four groups of age-0 juvenile flatfishes: Pacific halibut ( Hippoglossus stenolepis ), arrowtooth flounder ( Atheresthes stomias ), northern rock sole ( Lepidopsetta polyxystra ), and flathead sole ( Hippoglossoides elassodon ); and three groups of age-1 juvenile flatfishes: northern rock sole, flathead sole, and yellowfin sole ( Limanda aspera ). Sampling occurred at 33 sites across the continental shelf. Fish were collected using a 3-m beam trawl, and a midwater trawl. Environmental data were collected on sediment composition and water temperature and depth. Many of the age-species groups co-occurred in the Shumagin and Barnabus sea valleys; however, age-0 arrowtooth flounder occurred at more locations than other juveniles, perhaps due to a relatively broad tolerance of environmental conditions and to the utilization of midwater habitat. Thus, the large nursery area of arrowtooth flounder may be one reason why they are currently the most abundant GoA flatfish. In fact, among all species, mean recruitment at age 3 increased with the percent occurrence of age-0 juveniles at the 33 sites, a proxy for relative nursery area, in accordance with the nursery size hypothesis, suggesting that mean recruitment among GoA flatfishes is structured by nursery size. [ABSTRACT FROM AUTHOR]

Soft sediments in coastal shallow waters constitute nursery habitats for juveniles of several flatfishes. The quality of a nursery is defined by its capacity to optimize the growth and the survival of juvenile fish. The influence of biotic factors, such as food availability, is poorly studied at the scale of a nursery ground. Whether food availability limits juvenile survival is still uncertain. A spatial approach is used to understand the influence of food availability on the distribution of juvenile fish of various benthic and demersal species in the Bay of Vilaine (France), a productive nursery ground. We quantified the spatial overlap between benthic macro-invertebrates and their predators (juvenile fish) to assess if the latter were spatially covering the most productive areas of the Bay. Three scenarios describing the shapes of the predator–prey spatial relationship were tested to quantify the strength of the relationship and consequently the importance of food availability in determining fish distribution. Our results underline that both food availability and fish densities vary greatly over the nursery ground. When considering small organisational levels (e.g., a single fish species), the predator–prey spatial relationship was not clear, likely because of additional environmental effects not identified here; but at larger organisational level (the whole juvenile fish community), a strong overlap between the fish predators and their prey was identified. The evidence that fish concentrate in sectors with high food availability suggests that either food is the limiting factor in that nursery or/and fish display behavioural responses by optimising their energetic expenditures associated with foraging. Further investigations are needed to test the two hypotheses and to assess the impact of benthic and demersal juvenile fish in the food web of coastal nurseries. [ABSTRACT FROM AUTHOR]

Occurrence, distribution and prey items of juvenile marbled sole Pseudopleuronectes yokohamae were investigated around a submarine groundwater seepage on a tidal flat in southwestern Japan. Spatial distribution of radon-222 ( 222 Rn) concentration in water showed more submarine groundwater seepage in the offshore area. The lower salinities at offshore sampling stations corresponded with the highest 222 Rn concentrations. Juvenile marbled sole were collected from March through June with seasonal peak in April in 2013 and 2014. Mean abundance of juvenile marbled sole was highest at the second most offshore station where high submarine groundwater seepage was indicated. Major prey items in the stomachs of the marbled sole at the post-settlement stage (10–40 mm) were small crustaceans such as cumaceans and gammarids, which were partially replaced with polychaetes in larger juveniles (40–50 mm). Abundance of these major prey items was also higher at offshore stations. A negative correlation between gammarid abundance and salinity indicated a higher concentration of gammarids around the area of high submarine groundwater seepage, a pattern not observed for the other major prey organisms. Stable isotope analysis showed greater dependence of post-settlement stage marbled sole on the small crustaceans with low δ 13 C indicating that nutrients of terrestrial origin contribute to production of the juvenile marbled sole on the tidal flat. [ABSTRACT FROM AUTHOR]

Growth variability within individuals and among groups and locations and the phenomenon of summer growth reduction has been described for juvenile flatfish in a variety of European coastal areas whereby the underlying causes still remain elusive. Potential mechanisms were tested for juvenile plaice Pleuronectes platessa L. in the western Dutch Wadden Sea, by analysing published and unpublished information from long-term investigations (1986–present). Growth variability did occur and could be explained by differences induced by environmental variability (water temperature), and by non-genetic irreversible adaptation and sex. Dynamic Energy Budget analysis indicated that especially sexually-dimorphic growth in combination with variability in sex ratio could explain most of the variability in growth and the increase in the range of the size of individuals within the population over time. Summer growth reduction was not only observed among 0-group plaice in the intertidal, but also in the subtidal and tidal gullies as well as among I- and II-group plaice. Intraspecific competition for food was not detected but some support for interspecific competition with other predators was found. Also resource competition (due to crowding) with the other abundant epibenthic species (0-, I- and II-group flounder Platichthys flesus ; the brown shrimp Crangon crangon ; the shore crab Carcinus maenas ; the goby species Pomatoschistus minutus and Pomatoschistus microps ) could not explain the summer growth reduction. The observed growth reduction coincided with a decrease in stomach content, especially of regenerating body parts of benthic prey items. It is hypothesised that macrozoobenthos becomes less active after the spring phytoplankton bloom, reducing prey availability for juvenile plaice in summer, causing a reduction in food intake and hence in growth. [ABSTRACT FROM AUTHOR]

Flatfishes support a number of important fisheries in Alaskan waters and represent major pathways of energy flow through the ecosystem. Despite their economic and ecological importance, little is known about the use of habitat by juvenile flatfishes in the eastern Bering Sea. This study describes the habitat characteristics of juvenile flatfishes in coastal waters along the Alaska Peninsula and within the Port Moller–Herendeen Bay system, the largest marine embayment in the southern Bering Sea. The two most abundant species, northern rock sole and yellowfin sole, differed slightly in habitat use with the latter occupying slightly muddier substrates. Both were more common along the open coastline than they were within the bay, whereas juvenile Alaska plaice were more abundant within the bay than along the coast and used shallow waters with muddy, high organic content sediments. Juvenile Pacific halibut showed the greatest shift in distribution between age classes: age-0 fish were found in deeper waters (~ 30 m) along the coast, whereas older juveniles were found in the warmer, shallow waters within the bay, possibly due to increased thermal opportunities for growth in this temperature-sensitive species. Three other species, starry flounder, flathead sole, and arrowtooth flounder, were also present, but at much lower densities. In addition, the habitat use patterns of spring-spawning flatfishes (northern rock sole, Pacific halibut, and Alaska plaice) in this region appear to be strongly influenced by oceanographic processes that influence delivery of larvae to coastal habitats. Overall, use of the coastal embayment habitats appears to be less important to juvenile flatfishes in the Bering Sea than in the Gulf of Alaska. [ABSTRACT FROM AUTHOR]

A six-week trial was conducted to study the effects of different levels of organic carbon supplementation on biofloc color, structure and density, inorganic nitrogen and phosphorous dynamics, feed utilization and growth performance of Litopenaeus vannamei juveniles in an outdoor tank system under high-density and zero-exchange conditions. Organic carbon in the form of molasses was added daily to provide calculated carbon to nitrogen (C/N) ratios of 12:1 (CN-12), 15:1 (CN-15), and 18:1 (CN-18) based on the carbon–nitrogen content of the feed and the carbon content of the molasses during the entire experiment period No molasses was added in the control group which had a C/N ratio of 9 (CN-9). One additional treatment in which molasses supplementation was based on the actual level of total ammonia nitrogen (TAN) in the culture water (6 g of carbon was added for each 1 g of TAN as measured weekly), was also included and referred to as treatment CN-adjust. Juvenile shrimp (2.21 ± 0.11 g) were stocked into 20 experimental tanks filled with 500 L of biofloc-rich water. Each treatment had four randomly assigned replicate tanks stocked at a density of 300 shrimp m − 3 . Shrimp were fed a formulated feed with 36% crude protein and cultured for 6 weeks. One week after the trial initiation, the color of suspended bioflocs began to differentiate, ranging from green to brown corresponding with the increase in C/N ratios. The higher C/N ratios shifted the predominately autotrophic biofloc to heterotrophic, simultaneously displaying higher levels of volatile suspended solids. The concentrations of TAN, nitrite-nitrogen, nitrate‐nitrogen, total inorganic nitrogen, and reactive phosphorus of all treatments fluctuated, showing a decline in total inorganic nitrogen concentration and an increase in reactive phosphorus concentration with the increase in C/N ratios. All five treatments exhibited survival rates above 95.5% with no significant differences between treatments. Better shrimp final weights and growth rates, with significantly higher yields and lower feed conversion ratio values were found for treatments CN-9, CN-adjust, and CN-12 than the CN-15 and CN-18 treatments. Three significant conclusions can be drawn from the results of this study: (1) VSS and turbidity values were superior quantifying parameters for quantitative determination of biofloc than SS or TSS in a biofloc-based system; (2) once a mature biofloc community is established, TAN and NO 2 − –N concentrations can be effectively controlled by either heterotrophic assimilation or autotrophic nitrification that helps maintain their concentrations at acceptable ranges for shrimp culture even at high stocking densities; and (3) the mixed type of biofloc dominated by both microalgae and autotrophic bacteria is more beneficial for shrimp performance in high density zero-exchange culture systems than systems dominated by heterotrophic bacteria, and also reduces production costs by reducing organic carbon input and oxygen use. Statement of relevance This paper provides useful info concerning the role of organic carbon supplementations in biofloc-dominated tank system operated with no water exchange and the changes in selected water quality indicators and performance of the Pacific white shrimp, Litopenaeus vannamei under these conditions. [ABSTRACT FROM AUTHOR]

Cultured fish are often subjected to short-term fasting for a few days prior to transport or slaughter. This intervention reduces waste and oxygen consumption during transport and improves flesh quality, but little is known about how it affects the muscle lipid content. Even less is known for wild-caught fish that are also sometimes fasted before slaughter. To investigate the effects of short-term fasting on muscle lipid content, we performed three fasting experiments using adult, lean juvenile, and fatty juvenile red seabream ( Pagrus major ). In the first experiment using adult specimens (performed at 20 °C), fasting for 10 days caused up to 2.3-, 7.8-, and 3.7-fold increases in muscle mRNA levels of lipoprotein lipase 1 ( LPL1 ), LPL2 , and peroxisome-proliferator-activated receptor gamma ( PPAR γ), respectively (n = 6 each). These genes all participate in lipid accumulation. The second experiment was performed on 5 groups of lean juvenile red seabream [considered as wild-caught fish; 19 °C, n = 5 each except for one group (n = 4)]. Fasting for 5 days significantly increased muscle lipid content (percentage of wet weight) and LPL1 mRNA levels up to 2.2- and 11-fold, respectively. The mRNA levels of LPL2 and PPAR γ could not be determined possibly due to their low expression levels. The lipid amount (mg) in the liver decreased by 88% during fasting, whereas adipose tissue apparently disappeared after fasting for 10 days. These results suggest that lipid mobilization from liver and adipose tissue anticipated the muscular utilization of lipid, resulting in the counterintuitive increase in muscle lipid content during fasting. The third experiment was conducted on 7 groups of fatty juvenile red seabream [considered as cultured fish; 20 °C, n = 5 each except for one group (n = 4)]. Fasting up to 10 days did not increase muscle lipid content or LPL1 mRNA levels. The lipid amount in the liver, but not in the adipose tissue, decreased during the experiment. Fasting for 10 days was not enough to induce active lipid mobilization when fish were well fed prior to fasting. Contrary to our expectations, regression analysis using data from juvenile specimens found a significant inverse relationship between LPL1 mRNA levels and lipid amount in the liver, which might indicate that LPL1 mRNA levels are a reflection of temporal tissue demand for lipids. Overall, these results suggest that short-term fasting for ~ 5 days increases muscle lipid content of wild-caught lean fish possibly by an LPL1-dependent lipid transport mechanism. Statement of relevance We showed that short-term fasting improves flesh quality. [ABSTRACT FROM AUTHOR]

A 10-week experiment was conducted to estimate the effects of graded levels of histidine on growth performance, digested enzymes activities, erythrocyte osmotic fragility and hypoxia-tolerance of juvenile grass carp Ctenopharyngodon idella. Six isonitrogenous (38%) and isoenergetic semi-purified diets containing casein and gelatin with graded levels of histidine (0.45, 0.72, 1.02, 1.28, 1.55, 1.78 g 100 g − 1 DM) were formulated. Each diet was assigned to triplicate groups of 30 fish (3.68 ± 0.01) for each tank. The highest weight gain (WG, %), final body weight (FBW, g) and specific growth rate (SGR) were recorded when histidine level was 1.02% of the diet. Whole body protein and muscle protein were not significantly affected by the histidine level ( P > 0.05). Muscle histidine content was linearly increased along with the dietary histidine increasing ( P < 0.05). Fish fed histidine deficient diet (0.45 g 100 g − 1 ) exhibited highest erythrocyte osmotic fragility ( P < 0.05). Meanwhile, the shortest survival time and lowest catalase (CAT) activity and total antioxidant capacity were also recorded in fish fed histidine deficient diet ( P < 0.05). Second-degree polynomial regression analysis of final body weight data indicated that the minimum recommended dietary histidine requirement for grass carp was 1.21% of the diet, corresponding to 3.2% of dietary protein. Statement of relevance The present study determined optimum dietary histidine requirement for juvenile grass carp and the data goes to 1.21% of the diet, corresponding to 3.2% of dietary protein. We also found that juvenile grass carp fed with histidine deficiency diet not only limited their growth performance, but also exhibited higher erythrocyte osmotic fragility, lower hypoxia-tolerance and antioxidant enzyme activities. Digested enzyme activities were also significantly affected by the dietary histidine levels. Thus, it is important to meet histidine requirement when commercial diets are formulated for this species. [ABSTRACT FROM AUTHOR]

A feeding trial was conducted in a closed recirculating aquaculture system with Nile tilapia Oreochromis niloticus juveniles (mean weight, 6.81 g) to examine the response to a practical diet containing protein primarily from menhaden fish meal (FM) and soybean meal (SBM) (control, Diet 1) or to diets with decreasing ratios of PBM to SBM (Diets 2–7; dose–response) as a total replacement for digestible protein from FM, and the efficacy of 1% supplemental taurine (Tau) at the highest level of plant protein inclusion by removing Tau (Diet 8). To the extent possible, the replacement diets were formulated using currently published amino acid availabilities for the ingredients of interest in order to estimate and supplement the first two limiting amino acids (Met and Lys) to match levels in the FM control diet. The test diets were formulated to contain 35% digestible protein. Fish were fed three times daily all they would consume in 30 min. All performance measures were quadratic with respect to PBM:SBM ratio in the diet. The highest weight gain, lowest average daily feed intake, lowest feed conversion, and greatest specific growth rate coincided with a dietary PBM:SBM ratio of 1.22 to 1.35 suggesting that the best tilapia performance in the current trial was achieved with replacement formula D3 that contained approximately 20% SBM, 30% PBM, and supplemental Lys, Met, and Tau. However, all growth performance measures were significantly linear and decreased with respect to increasing distance from the ideal protein amino acid profile for tilapia. Positive effects of taurine supplementation at the highest level of dietary plant protein inclusion were not observed and may have been overwhelmed by imbalances in other amino acids in the test diets. The current results provide evidence that total deviation from the ideal protein profile in tilapia is an important consideration for diet formulation when combinations of diet ingredients are used. Hence, the essential amino acid content of a fish meal control diet may be an inadequate target for optimizing fish meal replacement diets for tilapia; whereas the whole body or muscle amino acid pattern may be a more useful formulation target. Finally, while the database of ingredients that have been evaluated in tilapia is growing, the industry will benefit from more efficient diets as long-term averages of amino acid composition and digestibility accrue for a variety of traditional and novel ingredients. Statement of Relevance : The current results provide evidence that it is the total deviations from a postulated ideal protein profile that is a more important consideration for diet formulation than the combination of diet ingredients used to meet that profile. Therefore, it should be possible to formulate least-cost fish meal replacement diets for tilapia, irrespective of ingredient combinations, and diet intact protein level, as long as a reasonable amino acid model is chosen and a fairly robust set of ingredient composition and digestibility data are available. [ABSTRACT FROM AUTHOR]

This two-factor experiment incorporating three photoperiods (12L:12D, 16L:8D and 24L:0D) and two feeding methods (manual and self-feeding) was carried out to determine their effect on the growth performance of striped knifejaw, Oplegnathus fasciatus . Thirty juveniles were stocked into each 300 L tanks in triplicate for each treatment and fed a commercial diet for 10 weeks. Two-way ANOVA revealed that both photoperiod and feeding method have significant effect on the final mean weight, weight gain (%) and feed efficiency (FE) (P < 0.05); however, their interaction did not produce any significant effect (P > 0.05). Although the growth parameters didn't have significant difference between manual and self-feeding in fish exposed to 12L:12D photoperiod (P > 0.05), fish under other two photoperiods showed significant improvement under self-feeding system compared to manual feeding (P < 0.05). Final mean body weights in fish under 16L:8D and 24L:0D were 119.7 and 124.0 g at manual feeding; however, increased to 128.0 and 133.7 g, respectively at self-feeding system. While two daily peaks of feed intake were observed in 12L:12D and 16L:8D photoperiods when self-feeders used, 24L:0D photoperiod showed only one morning peak. At the end, there was no significant difference in different stress indicators such as cortisol, glucose and total protein among the treatments (P > 0.05). Finally, the results suggested that the extended (16L:8D) and continuous (24 L:0D) photoperiods, and the provision of self-feeder could significantly improve the growth performance of striped knifejaw without changing the stress response. Statement of relevance This is the first report on the combined application of photoperiod manipulation and self-feeder on striped knifejaw, which revealed that the combination would help to improve the growth performance significantly. The indoor aquaculture industry, at least, will be benefited from the important insights achieved from this study to stimulate the growth performance of this commercially important species, which has great consumer demand in Japanese market. [ABSTRACT FROM AUTHOR]

Over a six-month trial, growth performance of juvenile tilapia Oreochromis niloticus , raised under biofloc cultivation, was recorded. Five treatments with three replicates and 237 juveniles per replicate at different C:N ratios were tested (10:1, 12.5:1, 15:1, 17.5:1, 20:1). Molasses was added every fourth day as the carbon source. Trials were performed in eighteen 3.14 m 3 circular tanks with constant aeration. Survival in all treatments with biofloc was similar and significantly higher (94.60 ± 2.03%) than in the control treatment (84.96 ± 1.53%). Best weight gain (g/day) occurred in the control treatment, but was influenced by low density. The 10:1 and 15:1 C:N treatments had similar weight gains, but not the 12.5:1 and 17.5:1 C:N treatments. Total production in the 10:1 ratio treatment was the highest (18.03 ± 0.25 kg m − 3 ), with slightly declining production, in this order: control (17.86 ± 0.16), 15:1 (17.73 ± 0.18), 12.5:1 (17.20 ± 0.28), 17.5:1 (16.44 ± 0.04), and 20:1 (16.28 ± 0.02). Water quality remained similar in all biofloc treatments, but lower concentrations of nitrogen compounds occurred in the 10:1 C:N ratio tanks. These results suggest a 10:1 C:N ratio provides good survival and growth of tilapia with no water exchange. Biofloc technology is a good strategy in areas where alkaline pH is a limiting factor for aquaculture activities because the pH decreases gradually as molasses is added. Statement of Relevance The success and permanence of aquaculture sector relies on the implementation of sustainable and environment-friendly technology, the BFT optimizes energy and resources during production, so our results contribute significantly to the sector. [ABSTRACT FROM AUTHOR]

Most of the studies devoted to assess the effects of ultraviolet radiation (UVR) on fishes have been done with early life stages (i.e., eggs and larvae) as they are the most vulnerable to these wavelengths; however, the effects of UVR on juveniles or adults are less clear. This study evaluated the effects of UVR and diet (i.e., rich and poor in ultraviolet-absorbing compounds; UVAC) on the metabolic rates (respiratory frequency) and behavior (prey capture time) of juveniles of the reef fish Patagonotothen cornucola , a common species inhabiting the intertidal areas of the Patagonian coast. UVR was a significant stress factor for P. cornucola by increasing its respiratory frequency, which could be related to the costs of repairing any cellular components damaged during the exposure. Fish exposed to UVR took more time to detect and capture their prey, which could lead to a reduction in the prey capture rates, with the concomitant effects on growth. In addition, juveniles feeding on rich-UVAC diet had a significant lower respiratory frequency than those feeding on poor-UVAC diet. This differential response was not evident in the prey capture time. In their natural environment, P. cornucola could feed on a varied diet and could also partially avoid the exposure to UVR by hiding under the rocks or macroalgae. Future studies should consider the broad variety of diets that could be found in rocky intertidal areas, and how their qualities (in terms of UVAC content) could help to counteract the UVR effects on juvenile fish. [ABSTRACT FROM AUTHOR]

Methods of calculating wildlife entanglement rates are not standardised between studies and often ignore the influence of observer effort, confounding comparisons. From 1997–2013 we identified 359 entangled Australian fur seals at Seal Rocks, south-eastern Australia. Most entanglement materials originated from commercial fisheries; most frequently entangling pups and juveniles. Using Generalized Additive Mixed Models, which incorporated observer effort and survey frequency, we identified that entanglements were observed more frequently amongst pups from July to October as they approached weaning. Neither the decline in regional fishing intensity nor changing seal population size influenced the incidence of entanglements. Using the models, we estimated that 302 (95% CI = 182–510) entangled seals were at Seal Rocks each year, equivalent to 1.0% (CI = 0.6–1.7%) of the site population. This study highlights the influence of observer effort and the value of long-term datasets for determining the drivers of marine debris entanglements. [ABSTRACT FROM AUTHOR]

Payaos or anchored FADs are used extensively in the Philippine tuna fishery. Currently, spatial regulations on FAD use are implemented with limited observance or understanding of their potential impacts. A combination of semi-structured interviews ( n =150) and a total of six focus group discussions ( n =61) from purse seine, ringnet and handline fishers of General Santos City provided a coarse indication of fishers' operational patterns and decisions on fishing tactics and strategies. Over a period of about 25 years, Filipino FAD fishers moved from inshore areas to offshore areas to catch oceanic tunas and FAD associated small pelagics and neritic tunas. Presently their catch rates are reported to be significantly higher at more distant sites. Due to the high density and spatial limitations of FADs deployment in nearshore areas, offshore deployment of FADs in a spatial network that is owned by a company has become a strategy to maintain hold of a fishing ground. Purse seine and ringnet fishers, as area specialists, operate from 70 to 1000 km from the fishing port and have an average reported catch rate of 14 t per set. Handline fishers which roam freely between FAD areas claimed by purse seine and ringnet fishing companies which operate from 90 to 1500 km from the fishing port with an average reported catch rate of 1.6 t per fishing trip. Strategic decisions on the deployment of FADs in fishing grounds were strongly modulated by availability of fishing space, environmental considerations and both experience and information on areas with good catches. Day to day tactical decisions were mainly explained by socially mediated information flows, weather patterns and economic factors, and to a lesser extent by fish behavior and regulations. [ABSTRACT FROM AUTHOR]

Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants that are widely detected in the environment, biota, and humans. In mammals, PBDEs can be oxidatively metabolized to form hydroxylated polybrominated diphenyl ethers (OH-BDEs). While studies have examined behavioral deficits or alterations induced by exposure to PBDEs in both rodents and fish, no study to date has explored behavioral effects from exposure to OH-BDEs, which have been shown to have greater endocrine disrupting potential compared to PBDEs. In the present study, zebrafish ( Danio rerio ) were exposed during embryonic and larval development (0–6 days post fertilization, dpf) to a PBDE metabolite, 6-hydroxy, 2,2′,4,4′ tetrabromodiphenyl ether (10–50 nM) and then examined for short and long-term behavioral effects. Exposed zebrafish tested as larvae (6 dpf) showed an altered swimming response to light–dark transitions, exhibiting hypoactivity in light periods compared to control fish. When fish exposed from 0–6 dpf were tested as juveniles (45 dpf), they showed an increased fear response and hyperactivity in response to tests of novel environment exploration and habituation learning. These results demonstrate that early life exposure to a PBDE metabolite can have immediate or later life (more than a month after exposure) effects on activity levels, habituation, and fear/anxiety. [ABSTRACT FROM AUTHOR]

A multistressor study was conducted to investigate interactive effects of nutritional status and salinity on osmoregulation of juvenile white sturgeon. Our hypothesis was that lower nutritional status would decrease the salinity tolerance of juvenile white sturgeon. A four-week feed restriction (12.5%, 25%, 50%, 100% of optimum feeding rate: OFR defined as the rate (% body weight per day) at which growth is maximal) trial was performed, and relevant indices of nutritional status were measured. Following the trial, sturgeon were acutely exposed to various salinities (0, 8, 16, 24 ppt) for 120 h, and relevant osmoregulatory measurements were made at 12, 72, and 120 h post-salinity exposures. The feed-restriction trial resulted in a graded nutritional response with the most feed-restricted group (12.5% OFR) showing the lowest nutritional status. The salinity exposure trial showed clear evidence that lower nutritional status decreased the salinity tolerance of juvenile white sturgeon. Increasing salinities resulted in significant alterations in osmoregulatory indices of all feeding groups; however, a significantly slower acclimatory response to 24 ppt was detected in the most feed-restricted group compared to the non-feed-restricted group (100% OFR). Furthermore, evaluation of the effect of nutritional status on the relationship between osmoregulatory measurements and body size showed that there was a significant negative relationship between osmoregulatory performance and body size within the most feed-restricted group. This suggests that there is a certain body size range (200–300 g based on our finding) where juvenile white sturgeon can maximize osmoregulatory capacity at a salinity of 24 ppt. [ABSTRACT FROM AUTHOR]

The current study aimed to evaluate the influence of lipoic acid (LA) supplementation (439.84 ± 6.71 mg LA/kg feed) on antioxidants responses throughout the time in intestine, liver and muscle of juvenile common carp Cyprinus carpio . Two experimental groups were fed during four weeks with a diet with or without LA. Glutathione-S-transferase (GST) activity, glutathione (GSH) content, antioxidant capacity against peroxyl radicals (ACAP) and lipid peroxidation (TBARS) were evaluated in these organs. Also, a technique to measure protein disulfide bonds and sulfhydryl groups was optimized for intestine samples. GST activity was significantly higher (p < 0.05) in intestine after two weeks of supplementation. GSH content was also significantly higher (p < 0.05) in intestine, liver and muscle of fish fed with LA after two and three weeks, respectively. Total capacity antioxidant against peroxyl radicals was significantly increased (p < 0.05) in the muscle of animals fed with LA after the fourth week. Concentration of disulfide bonds was higher in the intestine of fish fed with LA but this group also showed higher concentration of sulfhydryl groups (p < 0.05). It is concluded that supplementation with LA is a safe strategy to induce antioxidant responses and improves the antioxidant status in different organs of common carp. Two week of supplementation are required to induce antioxidant responses in intestine and liver and three week for muscle. [ABSTRACT FROM AUTHOR]

During the last quarter-century, management of Summer Flounder Paralichthys dentatus along the Atlantic coast resulted in significant increases in abundance such that rebuilding targets were recently achieved. Although spawning stock biomass is high, recruitment of young-of-the-year (YOY) Summer Flounder remains variable. Chesapeake Bay is one of the principal nursery areas for this species, but processes such as growth and survival that affect production of YOY Summer Flounder in this estuary have not been explored. Here, we investigated the relationship between abundance and size of Summer Flounder recruits from the 1988 to 2012 year classes in Chesapeake Bay. We also considered the effects of environmental factors on fish size because conditions in the bay vary spatially during the time that fish occupy nursery areas. To describe variations in Summer Flounder size, we used monthly length observations from 13,018 YOY fish captured by bottom trawl from the lower Chesapeake Bay and the James, York, and Rappahannock river subestuaries where Summer Flounder are commonly observed. We applied a generalized additive model to describe spatial, temporal, and environmental effects on observed fish size; we also considered the density of Summer Flounder and an index of productivity as factors in the model. Summer Flounder in Chesapeake Bay exhibited density-dependent and spatially related variations in mean length: larger fish were found mostly in the Bay and smaller fish in the subestuaries. Additionally, low (< 13 °C) and high (> 26 °C) temperatures and low salinities (< 10 psu) had a negative effect on fish size, indicating that individuals found in these environments were typically smaller than conspecifics inhabiting areas of moderate temperatures and higher salinities. Variable nursery habitat conditions in temperate estuaries affect fish size and, subsequently, may influence production of Summer Flounder year classes through effects on maturation and survival. As water temperatures in the mid-Atlantic region continue to increase, YOY Summer Flounder size may be negatively affected. [ABSTRACT FROM AUTHOR]

Density dependence of somatic growth has an important, but overlooked, impact on fisheries management advice. We therefore examined how growth relates to abundance in a case where growth has been observed to vary substantially in recent years, namely North East Atlantic mackerel, one of the most widespread and commercially important fish stocks in the North Atlantic. Growth of juvenile and early adult North East Atlantic mackerel was found to be decreasing since the late 1990s. Modelling showed that growth was related to density. Mean growth rate during the first year was tightly correlated with the density of juveniles and especially with juveniles from the previous cohort. This putative effect of juvenile density could be tracked in the length-at-age up to adult mackerel at commercially targeted sizes. However, as the mackerel grew towards adulthood, the effects of the same cohort became dominant. The effect of adult density was minor, but increasing with age. The ontogenetic progression in density dependant regulation of growth appeared to reflect the spatial dynamics (migration patterns) in the feeding season. This is the first time growth patterns quantified in the adult mackerel population have been linked to density related processes occurring within the nursery areas during the first year. These aspects of mackerel production have a substantial and direct impact on the management plan evaluations used when fisheries scientists provide advice for fisheries management. [ABSTRACT FROM AUTHOR]

To facilitate the upstream passage of small fish, corrugated culverts are often preferred over smooth pipes, due to the lower edge and mean cross sectional water velocities created. This benefit could be lost if greater intensities of turbulence induced by wall roughness cause instability and increase the energetic expense of fish locomotion. Common carp ( Cyprinus carpio ) swimming performance and behaviour were evaluated in a flume using four wall roughness treatments: smooth (control), small (SC), medium (MC), and large (LC) corrugations, dependent on corrugation wavelength and amplitude. Individual fish ( n = 128, mean ± S.D. total length [TL] = 86 ± 8 mm) swam at a mid-channel velocity of 0.5 m s −1 for 30 min or until fatigue. Swimming performance was quantified by: (a) success (completion of 30 min trial) or failure; and (b) the time to fatigue (endurance) of those that failed. To evaluate behaviour, fish head positions were tracked manually every second. Occupancy of the area within the MC and LC troughs (concave area where velocity was lowest) was recorded and the relationships between trough occupation and (i) TL and (ii) success tested. Differences were tested for between successful and failed individuals, and among treatments, for the following dependent variables: the total distance moved, the mean distance from the flume wall occupied (Fish D ), and mean velocity (Fish U ) and turbulent kinetic energy (Fish TKE ) experienced. Treatment did not influence frequency of success (38–58% per treatment) or time to fatigue. During the MC and LC treatments, troughs were occupied for part of the trial by 56 and 55% of individuals, respectively. Trough occupation was independent of TL in both treatments, and more common for successful fish than failures in the LC treatment. For successful fish, the total distance moved did not differ among treatments. Successful Fish D varied among treatments and was higher for the LC (mean ± S.E. = 93.2 ± 22.3 mm) than the SC (33.5 ± 2.8 mm) treatment. Despite the availability of lower velocity areas, median successful Fish U was higher in the LC treatment (0.51 m s −1 ) than in any other (median = 0.47 m s −1 , 0.44 m s −1 and 0.47 m s −1 in the MC, SC, and control treatments, respectively). Treatment did not influence successful Fish TKE which was consistently low (median = 5.3–7.7 J m −3 per treatment). Although occupation of the MC and LC troughs occurred, many individuals spent little time here, and areas with lower TKE were often occupied. Under the experimental conditions created, this study does not support the assumption that low velocity areas created by wall corrugations will improve culvert passage. [ABSTRACT FROM AUTHOR]

Exposure to oiled sediments can negatively impact the health of fish species. Here, we examine the effects of chronic exposure of juvenile southern flounder, Paralichthys lethostigma, to a sediment-oil mixture. Oil:sediment mixtures are persistent over time and can become bioavailable following sediment perturbation or resuspension. Juvenile flounder were exposed for 32 days under controlled laboratory conditions to five concentrations of naturally weathered Macondo MC252 oil mixed into uncontaminated, field-collected sediments. The percent composition of individual polycyclic aromatic hydrocarbons (PAHs) of the weathered oil did not change after mixing with the sediment. Spiked exposure sediments contained 0.04–395 mg/kg tPAH50 (sum of 50 individual PAH concentration measurements). Mortality increased with both exposure duration and concentration of sediment-associated PAHs, and flounder exposed to concentrations above 8 mg/kg tPAH50 showed significantly reduced growth over the course of the experiment. Evident histopathologic changes were observed in liver and gill tissues of fish exposed to more than 8 mg/kg tPAH50. All fish at these concentrations showed hepatic intravascular congestion, macrovesicular hepatic vacoulation, telangiectasia of secondary lamellae, and lamellar epithelial proliferation in gill tissues. Dose-dependent upregulation of Cyp1a expression in liver tissues was observed. Taxonomic analysis of gill and intestinal commensal bacterial assemblages showed that exposure to oiled sediments led to distinct shifts in commensal bacterial population structures. These data show that chronic exposure to environmentally-relevant concentrations of oiled sediments produces adverse effects in flounder at multiple biological levels. [ABSTRACT FROM AUTHOR]

In the present study, juvenile cobia, Rachycentron canadum L. were fed diets contaminated by two different sources of cadmium: squid viscera meal (SVM-Cd, organic form) and cadmium chloride (CdCl 2 –Cd, inorganic form). The Cd concentrations in fish diet were approximate 3.0, 5.0 and 10.0 mg Cd kg −1 for both inorganic and organic forms. In the control diet (0.312 mg Cd kg −1 diet, Cd mainly come from fish meal), no cadmium was added. The experiment lasted for 16 weeks and a statistically significant inverse relationship was observed between specific growth rate (SGR) and the concentration of dietary Cd. The SGR of cobia fed a diet with SVM-Cd increased at the lowest doses and decreased with the increasing level of dietary SVM. Fish fed diet contaminated SVM-Cd had significantly higher SGR than those fed diets contaminated CdCl 2 –Cd among the high Cd level diets treatments. The dietary Cd levels also significantly affected the survival rate of the fish. Among the hematological characteristics and plasma constituents, glutamic-pyruvic transaminase activities and alkaline phosphatase activities in serum and liver increased and hepatic superoxide dismutase activity decreased with the increasing dietary Cd levels. The cobia fed diet contaminated by high level of CdCl 2 –Cd had significantly higher ALP activity than cobia fed diet contaminated by high level of SVM-Cd. The results from these studies indicate no differences in toxicity response to dietborne SVM-Cd and CdCl 2 –Cd at a low level of Cd. However, at a higher level, cobia was more sensitive to dietborne CdCl 2 –Cd than SVM-Cd. Based on quadratic regression of SGR, The Cd concentrations was 3.617 mg kg −1 in the optimal diet, Cd source was SVM (126 mg Cd kg −1 in SVM) which stimulate the growth of cobia and the added level was determined to be 26.7 g kg −1 diet in the present study. Cd accumulations in the kidney of cobia fed both types of Cd were higher than other tissues, and the order of Cd accumulation in tissues were kidney > liver > intestine > gill > muscle. Iron accumulation in liver and kidney and calcium accumulation in vertebra and scale were also significantly affected by dietary Cd levels. [ABSTRACT FROM AUTHOR]

Florfenicol (FLC) and oxytetracycline (OTC) are the two most commonly used antibiotics for bacterial treatment in fish farming in Brazil, and because of their intensive use, the potential harmful effects on aquatic organisms are of great concern. This study evaluated the effects of environmental concentrations of FLC and OTC on the genetic material of juvenile tilapia ( Oreochromis niloticus ) erythrocytes by using the comet assay and the occurrence of micronuclei (MN) and other erythrocytic nuclear abnormalities (ENAs) after exposure to 96 hour. The comet assay showed that fish erythrocytes exhibited significantly higher DNA damage after exposure to environmental concentrations of FLC and OTC. Although MN was not observed, ENAs were significantly higher after exposure to FLC, indicating that ENAs are a better biomarker for FLC than MN. The results showed that environmental concentrations of FLC and OTC were genotoxic to erythrocytes of O. niloticus ; however, future studies on DNA damage recovery are needed. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effects of adding guar gum, a non-starch polysaccharide, to the diet of Mugil liza juveniles. The juveniles (mean weight = 0.38 ± 0.01 g) were fed one of three diets with increasing supplement levels (4%, 8%, and 12%) and a control diet without additional gum for 60 days, in order to evaluate the effects on zootechnical performance, proximate composition, liver parameters, morphological alterations to the intestinal tract, and modulation of gastrointestinal microbiota. The animals fed 8% and 12% gum presented a significantly lower mean final weight, weight gain, specific growth rate, food intake rate, and protein intake rate than the control. Adding gum to the diets also reduced the dry matter, crude protein, and carcass fat levels. All treatments with added gum resulted in increased liver glycogen, and the cholesterol levels were significantly reduced in fish fed 4% and 8% supplement levels. No intestinal morphological alterations were observed in the animals. However, a modulating effect was noted on the microbial community, altering the bacterial quantity and composition throughout the tract segments. The use of guar gum is not recommended in Mugil liza diets, at least above 4%. [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate the effects and mechanism of dietary Cu deficiency and excess on lipid metabolism in the liver, muscle and VAT of juvenile Pelteobagrus fulvidraco . To this end, yellow catfish were fed 0.76 (Cu deficiency), 4.18 (adequate Cu) and 92.45 (Cu excess) mg Cu kg − 1 diet, respectively, for 8 weeks. WG and SGR in the adequate Cu group were significantly higher than those in Cu deficiency and excess groups. In liver, Cu deficiency showed no significant effect on Cu and lipid contents, the activities of 6PGD, G6PD and FAS, and the mRNA levels of many tested genes, including 6PGD, G6PD, FAS, ACCα, PPARγ, LXR, HSL, PPARα and ATGL. Cu excess induced Cu accumulation, reduced the lipid content, FAS activity as well as the mRNA levels of 6PGD, G6PD, FAS, ACCα, PPARγ, HSL and ATGL. In muscle, dietary Cu levels showed no significant effects on lipid content, the activities of lipogenic enzymes and the mRNA levels of the most tested genes, including of 6PGD, G6PD, FAS, SREBP-1, PPARγ, HSL and LPL. In VAT, Cu and lipid contents, FAS activity, and the mRNA levels of 6PGD, G6PD, FAS, SREBP-1, LXR, PPARα and LPL were not significantly influenced by dietary Cu levels. Thus, the change of lipid contents among tissues could be related to the enzymatic activities and gene expression related to lipid metabolism. Different response patterns of enzymatic activities and gene expression in various tissues following dietary Cu levels indicated the tissue-specific regulatory effect by Cu. [ABSTRACT FROM AUTHOR]

A 90-day experiment was conducted to evaluate the effects of practical diets with different lipid contents on survival, growth performance and whole-body composition of juvenile tench ( Tinca tinca ). Five-month-old juveniles (34.48 ± 0.77 mm total length, 0.382 ± 0.08 g weight) were fed practical diets with different lipid contents: 6.5%, 8.5%, 10%, 12%, 14%, 15.5% or 18%. Survival rates ranged from 96.7% to 100%. The highest growth was obtained with diets containing 8.5, 10 and 12% lipid. The five intermediate lipid contents (between 8.5% and 15.5%) caused lower FCRs (1.27–1.38). The percentages of fish with externally visible deformities were around 12%, with no significant differences due to the dietary lipid level. The relation among fatty acid profiles of the diets, body composition, growth performance of juveniles and requirements of other fish species is discussed. [ABSTRACT FROM AUTHOR]

An 18-week feeding trial was carried out under controlled conditions to compare the effects of l -carnitine at six levels (10, 150, 350, 650, 950 and 1250 mg kg − 1 ) on the growth performance, nutritional efficiency indices, hemolymph indices and finally, biological responses against 12-h air exposure challenge of juvenile (7.58 ± 0.39 g) crayfish Astacus leptodactylus leptodactylus . The significantly ( p < 0.05) highest values of final weight (63.58 g) and SGR (1.67% day − 1 ) and the lowest FCR (2.11) were observed in the juvenile crayfish fed the diet containing 650 mg kg − 1 l -carnitine. With an increment in the dietary l -carnitine levels, VFI increased significantly ( p < 0.05) from 2.28 to 3.66% BW day − 1 . The crayfish fed the levels of dietary l -carnitine higher than 350 mg kg − 1 showed the significantly ( p < 0.05) higher values of PER and PPV compared with those of fed 10, 150 and 350 mg kg − 1 . The significantly ( p < 0.05) lowest LPV was observed in crayfish fed the diets containing 650 and 950 mg kg − 1 l -carnitine. The juvenile crayfish fed the diet containing 650 mg kg − 1 l -carnitine had the significantly ( p < 0.05) highest THC (105.36 × 10 5 cell ml − 1 ), PO (7.03 U min − 1 ), SOD (4.83 U min − 1 ), GSH (3.53 mg g − 1 protein), GPX (4.23 mg g − 1 protein) and TBARS (4.40 mg g − 1 protein). There was an inverse trend between SOD and TBARS. After 12-h air exposure challenge, the juvenile crayfish fed the diet containing 650 mg kg − 1 l -carnitine showed significantly ( p < 0.05) highest activities of THC, PO, SOD, GSH and GPX. The dietary l -carnitine level of 650–950 mg kg − 1 could improve growth performance, feed utilization and antioxidant defence system. Polynomial regression of SGR, FCR, PPV, PER and LPV suggested that the optimum dietary l -carnitine level could be higher than 350 and < 950 mg kg − 1 in crayfish reared in culture conditions. [ABSTRACT FROM AUTHOR]

Critical windows are periods of developmental susceptibility when the phenotype of an embryonic, juvenile or adult animal may be vulnerable to environmental fluctuations. Temperature has pervasive effects on poikilotherm physiology, and embryos are especially vulnerable to temperature shifts. To identify critical windows, we incubated whitefish embryos at control temperatures of 2 °C, 5 °C, or 8 °C, and shifted treatments among temperatures at the end of gastrulation or organogenesis. Heart rate (f H ) and oxygen consumption ( V ˙ O 2 ) were measured across embryonic development, and V ˙ O 2 was measured in 1-day old hatchlings. Thermal shifts, up or down, from initial incubation temperatures caused persistent changes in f H and V ˙ O 2 compared to control embryos measured at the same temperature (2 °C, 5 °C, or 8 °C). Most prominently, when embryos were measured at organogenesis, shifting incubation temperature after gastrulation significantly lowered V ˙ O 2 or f H . Incubation at 2 °C or 5 °C through gastrulation significantly lowered V ˙ O 2 (42% decrease) and f H (20% decrease) at 8 °C, incubation at 2 °C significantly lowered V ˙ O 2 (40% decrease) and f H (30% decrease) at 5 °C, and incubation at 5 °C and 8 °C significantly lowered V ˙ O 2 at 2 °C (27% decrease). Through the latter half of development, V ˙ O 2 and f H in embryos were not different from control values for thermally shifted treatments. However, in hatchlings measured at 2 °C, V ˙ O 2 was higher in groups incubated at 5 °C or 8 °C through organogenesis, compared to 2 °C controls (43 or 65% increase, respectively). Collectively, these data suggest that embryonic development through organogenesis represents a critical window of embryonic and hatchling phenotypic plasticity. This study presents an experimental design that identified thermally sensitive periods for fish embryos. [ABSTRACT FROM AUTHOR]

Changes in ambient temperature affect the physiology and metabolism and thus the distribution of fish. In this study we used intermittent flow respirometry to determine the effect of temperature (2, 5, 10, 15 and 20 °C) and wet body mass (BM) (~ 30–460 g) on standard metabolic rate (SMR, mg O 2 h − 1 ), maximum metabolic rate (MMR, mg O 2 h − 1 ) and metabolic scope (MS, mg O 2 h − 1 ) of juvenile Atlantic cod. SMR increased with BM irrespectively of temperature, resulting in an average scaling exponent of 0.87 (0.82–0.92). Q 10 values were 1.8–2.1 at temperatures between 5 and 15 °C but higher (2.6–4.3) between 2 and 5 °C and lower (1.6–1.4) between 15 and 20 °C in 200 and 450 g cod. MMR increased with temperature in the smallest cod (50 g) but in the larger cod MMR plateaued between 10, 15 and 20 °C. This resulted in a negative correlation between the optimal temperature for MS (T opt ) and BM, T opt being respectively 14.5, 11.8 and 10.9 °C in a 50, 200 and 450 g cod. Irrespective of BM cold water temperatures resulted in a reduction (30–35%) of MS whereas the reduction of MS at warm temperatures was only evident for larger fish (200 and 450 g), caused by plateauing of MMR at 10 °C and above. Warm temperatures thus seem favourable for smaller (50 g) juvenile cod, but not for larger conspecifics (200 and 450 g). [ABSTRACT FROM AUTHOR]

A new method to increase escape rate of juvenile fish from trawl codend was developed. The method encourages fish to approach the netting by generating an active shaking motion using a cap-like canvas at the end of the codend. Three types of model codend were used: a traditional codend, a fluttering flag-like netting panel and a double conical rope array used as an active stimulating device (ASD). The escape responses of juvenile bastard halibut ( Paralichthys olivaceus ) and juvenile red seabream ( Pagrus major ) were observed in a circulating water channel. The amplitude ratio of the shaking distance was 0.6–0.8 of the codend diameter and its period was 3–4 s. The escape rate was 22–30% higher in the shaking codends than in steady codends. The relative lateral moving speeds of the escaping fish were 1.4–1.7 times higher when shaking occurred than when no shaking occurred. The sieving effect of the shaking codend operated to actively drive fish to the netting panels and weakened the optomotor response of fish, possibly by generating erratic movement, allowing more fish to escape, and resulting in a reduction of the juvenile by-catch. [ABSTRACT FROM AUTHOR]

Assessing juvenile Argentine hake stocks from the area swept by bottom-trawls has systematically produced underestimates, given the adult population levels recruited from them. To gain insight into the behavior and vertical distribution of first-year Argentine hake, acoustic data and both pelagic and bottom-trawl net samples were collected in the nursery ground of the southern stock. Five surveys were carried out in the austral winters and summers from June 2011 to February 2013. Daylight echograms at 38 kHz showed horizontally extended aggregations of young-of-the-year (YOY) hake as layers 10-20 m thick separated from the seabed at average distances of 15-20 m in winter and 10-15 m in summer. They were above the reach of the bottom trawl nets routinely used in hake assessments. While close agreement of total length distributions was found between net samples and acoustic fish-track data in the juvenile's first winter, only the smaller fraction of the bimodal distribution shown by the acoustic data was present in pelagic trawl catches six months later, in the following summer. That suggests the larger fish can avoid the survey nets. Detection and assessment with acoustic methods allowed determination of the mean densities and horizontal distribution patterns of early juveniles in their main nursery ground. The mean juvenile densities obtained with acoustic methods were above one order of magnitude higher than those obtained by bottom trawls using the swept-area method. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effects of 21-days exposure to EDCs in an estuarine fish. [•] Vtg-like proteins were significantly induced by E2 in juveniles fish. [•] The mode of action of PCB-77 seems to be dependent of the fish life stage. [•] Vtg arises as a biomarker for EDC biomonitorization on juvenile P. microps. [ABSTRACT FROM AUTHOR]

Highlights: [•] The growth was decreased with increasing of both forms of Cu doses. [•] Copper was increased in all tissues with increasing of both forms of Cu doses. [•] The remaining tissues and the liver contributed most of the total Cu in the body. [•] Either Cu-NPs or CuSO4 caused tissues oxidative stress and cell apoptosis. [•] Dissolved Cu was more toxic than Cu-NPs. [Copyright &y& Elsevier]

Highlights: [•] Surveys of seagrass meadow fish assemblages in Great Britain. [•] Seagrass contains higher fish abundance and richness than adjacent sand. [•] 9 commercial fish species as juveniles in seagrass, most abundant were Plaice, Pollock and Herring. [•] First evidence of juvenile fish of commercial value in seagrass surrounding Great Britain. [Copyright &y& Elsevier]

As temperature-based growth trials are lengthy, expensive and laborious to run, juvenile hapuku (Polyprion oxygeneios) were employed to assess whether respirometric tests and behavioural preference methods could be used to resolve the optimum temperature for growth and feed conversion efficiency in novel culture species. On the basis that the energetic costs of rapid growth are substantial and need to be accommodated physiologically, it was hypothesised that maximal growth and optimal feed conversion (feed conversion ratio, FCR) would be maximised at temperatures where aerobic metabolic scope (AMS) was also maximised. It was further hypothesised that hapuku would behaviourally self-select temperatures that lead to the greatest level of AMS, growth and FCR performance. Acclimating hapuku juveniles to 12, 15, 18, 21 and 24°C for 4weeks resulted in a peak in specific growth rate (SGR) at 18 and 21°C with slower growth at lower and higher temperatures. AMS was also maximal between 18 and 21°C and was therefore tightly linked with SGR. The behavioural thermal preference (Tpref) range of hapuku also fell within the optimum range for growth. FCR, however, was inversely related to temperature with the most and least efficient rates of conversion occurring at 12°C and 24°C respectively. Though AMS and Tpref had no utility in predicting the optimal range for FCR, standard metabolic rate (SMR) showed a positive linear relationship to FCR. The conclusions of the study are threefold: 1) Hapuku select temperatures that optimise both AMS and growth. 2) AMS and Tpref appear tightly linked with SGR and could possibly be used to predict the optimum temperature for growth in novel species. 3) AMS and Tpref have no utility in predicting the optimum temperature for FCR. [ABSTRACT FROM AUTHOR]

Abstract: A growth trial lasting for 12weeks was conducted in a semi flow-through system to determine the dietary potassium requirement of juvenile grass carp (Ctenopharyngodon idellus) with an initial body weight of 4.8g. Seven isonitrogenous and isoenergetic semi-purified diets were compounded with different dietary potassium levels: 1.50, 2.32, 3.28, 5.30, 7.12, 9.45 and 10.44gkg−1 diet. The results showed that specific growth rate and feed efficiency of grass carp were significantly (P <0.05) affected by dietary potassium level, the highest value of specific growth rate was in 5.30gkg−1 group and feed efficiency values in 5.30, 7.12 and 9.45gkg−1 groups were significantly higher than those in the other groups. The survival rate of grass carp in the present study was not affected by dietary potassium level (P >0.05). The Na+–K+ ATPase activity value in the gills varied significantly (P <0.05) with dietary potassium level and showed an increasing and then decreasing trend, and the highest value was in the 7.12gkg−1 group. Dietary potassium level showed significant (P <0.05) effect on serum SOD, ALP and AST activities. SOD and ALP activities increased and then decreased as potassium level increased, while AST decreased first and then increased. Serum TP and TC contents increased and then decreased with potassium level (P <0.05). TG, ALT and BUN were not affected by dietary potassium level (P >0.05). Body potassium and moisture contents increased and lipid content decreased with dietary potassium content, while ash content in fish body increased first and then decreased as potassium content increased (P <0.05). Body protein in the 10.44gkg−1 group was significantly lowered (P <0.05). However, calcium, magnesium, phosphorus and sodium contents in dry matter were not affected by dietary potassium level. When the potassium content of water was 1.86–3.10mgL−1, judging from the polynomial regression analysis for the specific growth rate of fish and the Na+–K+ ATPase activity in the gill, and the broken-line analysis for body potassium content, the optimal dietary potassium content for juvenile grass carp was 4.65, 7.27 and 5.98gkg−1 diet respectively. [Copyright &y& Elsevier]

Abstract: An 8-week feeding trial was conducted to investigate the effect of various levels and sources of dietary phospholipids (PL) on growth performance and fatty acid composition of juvenile Portunus trituberculatus. Six semi-purified diets were formulated to contain one control group, three levels of soybean lecithin (SL1%, SL2%, SL4%) and two levels of egg yolk lecithin (EL1%, EL2%), but remaining isolipidtic and isonitrogenous. Each diet was fed in triplicates (18 crabs replicate−1, initially weighing 22.22±0.08g). The dietary PL supplementation groups (except the group of SL 2%) had significantly higher weight gain (WG), special growth ratio (SGR) and final body wet weight (FBW) than the control group (P <0.05). Moreover, crabs fed diets with 2% EL supplementation showed higher SGR than 2% SL supplemented group (P <0.05). With PL supplementation, we also observed that the highly unsaturated fatty acids (HUFA) percentage of the hepatopancreas and muscle increased with a decrease in the polyunsaturated fatty acid (PUFA) level. Compared with the control group, crabs fed diets with EL supplementation had higher n-3/n-6 ratio in muscle (P <0.05). Compared with hepatopancreas, higher level of HUFA (especially for C20:5n-3) and lower PUFA level were observed in muscle. Based on growth performance, this study suggested that 1% PL (SL or EL) supplemented in diets could satisfy the requirement of juvenile P. trituberculatus. Moreover, crabs fed diets with EL supplementation had a higher nutritional value of fatty acid profiles than SL groups. [Copyright &y& Elsevier]