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Many philosophers and Effective Altruist researchers have argued that the overall welfare of wild fish is negative. Since there are more fish than any other kind of wild vertebrate on earth (even when taken together), the view that suffering is predominate among wild fish is a key part of their larger suggestion that the overall welfare of wild vertebrates is negative, a view I'll call 'wildlife pessimism.' Correspondingly, undermining the wildlife pessimist's view might largely be accomplished simply by taking a closer look at their arguments concerning fish. Focusing on fish alone will allow for a greater depth of empirical analysis than has hitherto been possible in the wildlife welfare debate, which usually features attempts to discuss all wild animals at once. As I will show, wildlife optimism is at least as likely as wildlife pessimism. That is, it seems just as plausible that wild fish have a welfare level that is neutral or positive overall. [ABSTRACT FROM AUTHOR]

Lumpfish (Cyclopterus lumpus) are raised as cleaner fish for controlling sea lice. Intensive rearing is complicated by fin nipping that occurs between juvenile conspecifics. Lumpfish density‐dependent interactions are not well understood; therefore, the effects of rearing density for different fish size classes warranted evaluation. Two size classes (2‐ and 13‐g) of juvenile lumpfish were stocked at four different rearing densities (40, 60, 70, and 90 g/L) with growth, survival, and fish aggression assessed over 8 weeks. Mean weight gain and specific growth rates ranged from 170% to 307% and 1.77% to 2.50%, respectively, depending on density treatments, for the 2‐g fish, and from 286% to 471% and 2.42% to 3.10% for the 13‐g fish. Growth was negatively correlated with density, with faster growth linked to lower densities. No mortality occurred in any treatment and significant fish aggression only occurred among the larger lumpfish in the higher rearing densities. Based on these findings, growth of 2‐g lumpfish can be increased if reared at 40 g/L or slowed at 70 g/L without impacting aggression. For grow out of 13‐g fish to ~70 g with minimal aggression, a 40 g/L rearing density is recommended for faster growth and 60 g/L for slower growth. [ABSTRACT FROM AUTHOR]

There is an increased demand for tuna meat to supply the growing global sushi and sashimi market. Current methods to farm tunas, especially Atlantic bluefin tunas (ABFTs; Thunnus thynnus), are unsustainable. This is driving a movement towards closed-cycle ABFT aquaculture, i.e., farming tuna from spawning and hatching to slaughter on land, to try and meet the demand for these fish. Tunas are not domesticated species and thus face different challenges in terms of closed-cycle aquaculture when compared to other farmed fish species. Tunas also possess unique physiological traits such as regional endothermy and ram ventilation which affect their needs and how they are farmed. No current global standards exist to measure or monitor ABFT welfare in captivity, because there are many unknown factors surrounding ABFT welfare in aquaculture settings. There is a need to conduct studies that measure the baseline physiological parameters of ABFT in closed-cycle systems. Issues such as manipulation of breeding cycles, tank design, and slaughter procedures need attention and further research is required before such welfare indicators can be established. Stress is an overarching concern for animal welfare. In particular, pre-slaughter crowding and stress negatively affect the quality of the meat produced due to lactic acid buildup in the red muscle. Further research needs to be conducted throughout all life stages in terms of both animal welfare implications and the commercial viability of farmed ABFTs. [ABSTRACT FROM AUTHOR]

There is an increased demand for tuna meat to supply the growing global sushi and sashimi market. Current methods to farm tunas, especially Atlantic bluefin tunas (ABFTs; Thunnus thynnus), are unsustainable. This is driving a movement towards closed-cycle ABFT aquaculture, i.e., farming tuna from spawning and hatching to slaughter on land, to try and meet the demand for these fish. Tunas are not domesticated species and thus face different challenges in terms of closed-cycle aquaculture when compared to other farmed fish species. Tunas also possess unique physiological traits such as regional endothermy and ram ventilation which affect their needs and how they are farmed. No current global standards exist to measure or monitor ABFT welfare in captivity, because there are many unknown factors surrounding ABFT welfare in aquaculture settings. There is a need to conduct studies that measure the baseline physiological parameters of ABFT in closed-cycle systems. Issues such as manipulation of breeding cycles, tank design, and slaughter procedures need attention and further research is required before such welfare indicators can be established. Stress is an overarching concern for animal welfare. In particular, pre-slaughter crowding and stress negatively affect the quality of the meat produced due to lactic acid buildup in the red muscle. Further research needs to be conducted throughout all life stages in terms of both animal welfare implications and the commercial viability of farmed ABFTs. [ABSTRACT FROM AUTHOR]

Purpose: A limited number of studies have aimed at understanding behavior towards animal welfare. However, there are indications that consumers make an important distinction between land animals and fish. As no studies have attempted to explain the factors that influence consumer behavior towards the welfare of fish, this study aims to explain the behavior using the value–belief–norm (VBN) model. In addition, we extend the model by using empathy as a factor influencing the formation of personal norms. This study argues that by adding empathy to the model, we will improve the ability of the VBN to explain moral behavior. Design/methodology/approach: The study is based on survey data from 416 Norwegian consumers. A structural equation modeling analysis with latent constructs is used to test the hypotheses. Findings: The findings validate the ability of the VBN model to explain consumer intention to buy products containing fish with better welfare. We also showed that empathy and beliefs strongly influence personal norms. The extended VBN model increased the explained variance of personal norm by 11,54%. Consumers with biospheric values are strongly likely to have empathetic feelings towards fish suffering and believe that fish can feel pain. However, consumers with hedonistic values are significantly negatively related to beliefs and empathy. Practical implications: By understanding the role of empathy, companies can develop marketing strategies that appeal to consumers' values, empathy and beliefs and ultimately encourage them to make purchases that support fish welfare. Originality/value: Practically, this study explores consumers' beliefs towards fish welfare and identifies consumers who are more likely to purchase products containing fish with better welfare based on their values. [ABSTRACT FROM AUTHOR]

In this study, we described immediate/acute reactions to stress-related chemical cues (SC – Stress Cue) in fish. Specifically, we evaluated the effects of SC on ventilation rate (VR) and feeding behavior in Nile tilapia (Oreochromis niloticus), a highly relevant species for world aquaculture, therefore, to understand the diversity of stressful contexts and stress responses in this species have important practical applications (stress reduction). Stress cue was obtained from conspecifics exposed to a handling stressor. Stress was confirmed by measuring plasma cortisol levels. The responses to SC were contrasted to chemical control cues: a cue originated from non-stressed conspecifics and pure water (vehicle control). We observed that Nile tilapia exposed to SC had an increase in VR, but without effects on feeding behavior (feeding latency and ingestion). Thus, the SC is a stressor that induces readily stress response (VR increase), suggesting sympathetic activation, but did not change feeding performance. In practical terms, it is positive because although social propagation of stress via SC elicits a stress response, it did not harm appetite. [ABSTRACT FROM AUTHOR]

The stress‐coping ability (SCA) is one of the core aspects of fish welfare and is of vital importance for fish production in the aquaculture industry and for fish fitness in hatchery release. Environmental enrichment (EE), a method of introducing external stimuli into the husbandry environment, has been recently proposed to improve fish SCA, but the present experimental evidence is mixed, and the reasons for these discrepancies are unclear. Here, we conducted a global meta‐analysis using a data set that consists of 1786 cases from 107 studies across 42 fish species to solve this problem. Overall, we found that enriched fish had significantly higher SCA than control fish, reflected in either basal stress levels or stress responses. Meta‐regression analyses showed that specific subgroups of enrichment type, fish developmental stage, stress category, stress duration, stress place, sample tissue and indicator system showed significant positive EE effects on SCA. Multi‐model inference indicated that the indicator system, fish developmental stage, stress characteristic and enrichment mode are important drivers for the high heterogeneity among effect sizes. These results highlight the importance of introducing EE into the rearing systems, which will not only increase the welfare of aquaculture fish but also improve the ecological adaptability of released fish. The comprehensive knowledge obtained in this analysis will provide insights into fish ontogenetic plasticity and its responses to EE and have important implications for improving the production cycle in fish aquaculture and fisheries conservation. [ABSTRACT FROM AUTHOR]

Billions of fishes are kept in captivity for research and food production world‐wide, with a strong impetus for maintaining high welfare standards. Accordingly, the importance of empirical research into the welfare and husbandry of captive fishes is increasingly acknowledged in both science and aquaculture, alongside growing public and governmental interest. Physical enrichment can have an important influence on welfare in of captive fishes, but many questions remain. Here, we summarise the current state of research and outline knowledge gaps in the area of physical enrichment, which is a fundamental aspect to improving welfare of captive fishes. To explore the level of research interest this area across time we conducted a series of surveys, using the number of papers published per year as a metric. These surveys highlight that work on fish welfare, while representing a relatively low proportion of fish research overall, is increasing rapidly. For species that are of aquaculture importance or used commonly as laboratory subjects, we show a positive relationship between general research interest and number of welfare‐related papers. However, for many, particularly relatively less studied, species the proportion of papers on enrichment remains low, with a slower increase compared to welfare‐related papers in general. In terms of common metrics used to quantify fish welfare, there is a reliance on growth and behaviour, with scope for inclusion and combination of a more comprehensive range of reproducible measures. We finish by highlighting recent progress, promising areas for future research and suggestions for advances in this area. [ABSTRACT FROM AUTHOR]

The present study aimed to determine the anaesthetic effectiveness, safety, and applicable concentrations of coriander (Coriandrum sativum) essential oils (CEO) for three-spotted tilapia (Oreochromis andersonii). For this purpose, CEO concentrations of 400, 500, and 600 µL/L were tested at two temperatures, 20.90 ± 1.19 °C and 30.60 ± 0.92 °C, on three different sizes (small, medium, and large) of the fish in duplicate glass aquaria with 200 mg/L of tricaine methanesulfonate (MS-222) served as the control. The sedative efficacy during simulated transportation experiments was also carried out. The results demonstrated that the induction and recovery time in O. andersonii anaesthetised with CEO were significantly influenced by concentration, water temperature, and fish size (P < 0.05). A concentration of 600 µL/L of CEO was found to be highly effective in inducing deep anesthesia and promoting rapid recovery in small and medium-sized fish at both water temperatures (20 and 30 °C). Based on this study, 100 µL/L of CEO is recommended for short-term transportation lasting up to 4 h, while 50 µL/L is advised for longer-distance transport. Although coriander essential oil shows anaesthetic effectiveness in three-spotted tilapia, further research is needed to fully understand the efficacy and safety of CEO across different fish species. [ABSTRACT FROM AUTHOR]

DNA methylation clocks provide information not only about chronological but also biological age, offering a high-resolution and precise understanding of age-related pathology and physiology. Attempts based on transcriptomic and epigenetic approaches arise as integrative biomarkers linking the quantification of stress responses with specific fitness traits and may help identify biological age markers, which are also considered welfare indicators. In gilthead sea bream, targeted gene expression and DNA methylation analyses in white skeletal muscle proved sirt1 as a reliable marker of age-mediated changes in energy metabolism. To complete the list of welfare auditing biomarkers, wide analyses of gene expression and DNA methylation in one- and three-year-old fish were combined. After discriminant analysis, 668 differentially expressed transcripts were matched with those containing differentially methylated (DM) regions (14,366), and 172 were overlapping. Through enrichment analyses and selection, two sets of genes were retained: 33 showing an opposite trend for DNA methylation and expression, and 57 down-regulated and hypo-methylated. The first set displayed an apparently more reproducible and reliable pattern and 10 multifunctional genes with DM CpG in regulatory regions (sirt1, smad1, ramp1, psmd2—up-regulated; col5a1, calcrl, bmp1, thrb, spred2, atp1a2—down-regulated) were deemed candidate biological age markers for improved welfare auditing in gilthead sea bream. [ABSTRACT FROM AUTHOR]

Environmental enrichment is a reliable and useful tool for improving fish welfare in farms. Structural enrichment is widely studied and applied to fish, with positive effects also on the zootechnical parameters of fish farming. In our study, we examined whether artificial shelters and water hyacinth - structural enrichments - improve the quality of tilapia fillets. Tilapia juveniles (n = 480) underwent three independent treatments over 100 days: artificial water hyacinth enrichment, shelter enrichment, and control (no enrichment). After slaughtering, we evaluated physical-chemical indicators of meat quality. Whereas meat pH was not affected by the availability of enrichment, we found less lightness in terms of chroma b* of the flesh from tilapia raised with artificial water hyacinth and more flesh toughness in the texture of tilapia raised with shelter, indicating a higher-quality product. Regarding the fatty acid profile, differences were found when individually analyzed. All fatty acids that differed among treatments (C4:0, C23:0, C24:0, C16:1, and C24:1) exhibited better performance in groups reared with structural enrichment. In conclusion, improving Nile tilapia welfare with structural enrichment enhances its flesh quality. Thus, in addition to promoting the welfare of farmed fish, this enrichment may benefit both farmers and consumers. [ABSTRACT FROM AUTHOR]

The aim of this study was to test the impact of replacing vegetable oils commonly used in the feed of Arctic char (Salvelinus alpinus) with biomass of the oleaginous yeast Rhodotorula toruloides. For that, a control feed containing vegetable oils and an experimental feed including yeast biomass at 15% level, were fed to Arctic char. Sensory properties of the fish were tested. The content of undesirable compounds in the new feed ingredient were evaluated. Selected heavy metals and organic pollutants were measured in the yeast biomass and the levels found were below the limits of the regulations defined by the European Union. Moisture and ash contents were similar between the two feeds. Hepatic activity of 7-ethoxyresorufin-O-deethylase was evaluated between the two fish groups and no significant differences were observed. The sensory analysis conducted on heat treated fish fillets with untrained volunteers showed no perceptible sensory difference. [ABSTRACT FROM AUTHOR]

Society is becoming more demanding with aquaculture's environmental footprint and animal wellbeing. In order to potentially mitigate these concerns, feed formulations could be based on eco-efficient (circular economy-driven) or organic ingredients. This study aimed to investigate the growth performance, feed utilization, and health status of juvenile Nile tilapia (Oreochromis niloticus) when fed with such feeds. The growth trial lasted for 8 weeks, and fish had an initial weight of 31.0 ± 0.5 g (mean ± SD). Fish were fed until visual satiation, in quadruplicate, with one of three isonitrogenous and isoenergetic experimental feeds: a commercial-like feed without fishmeal (PD), a diet based on ingredients compatible with organic certification (ORG), or a feed formulated using circular economy-driven subproducts and emergent ingredients (ECO). Fish fed ECO showed a tendency for decreased feed intake, while ORG fish significantly reduced their intake compared to those fed PD. Consequently, fish fed ECO (62.7 ± 5.4 g) exhibited almost half the growth than those fed PD (107.8 ± 6.1 g), while ORG fish almost did not increase their weight (32.7 ± 1.3 g). ECO and ORG diets had a lower digestibility for protein, lipid, and energy when compared to PD. Feed utilization of fish fed ECO or ORG was also lower than those fed PD. From the health-related genes analyzed, only glutathione reductase (gsr) showed statistically significant differences, being more expressed in fish-fed ECO than those fed PD. Thus, even when such novel formulations induced extreme effects on voluntary feed intake, their impact was noted only in fish growth, but not in robustness. [ABSTRACT FROM AUTHOR]

Aquafeed's contamination by microplastics can pose a risk to fish health and quality since they can be absorbed by the gastrointestinal tract and translocate to different tissues. The liver acts as a retaining organ with the consequent triggering of oxidative stress response. The present study aimed to combine the use of natural astaxanthin with natural-based microcapsules to counteract these negative side effects. European seabass juveniles were fed diets containing commercially available fluorescent microplastic microbeads (1–5 μm; 50 mg/kg feed) alone or combined with microencapsulated astaxanthin (AX) (7 g/kg feed; tested for half or whole feeding trial—30 or 60 days, respectively). Fish from the different dietary treatments did not evidence variations in survival and growth performance and did not show pathological alterations at the intestinal level. However, the microplastics were absorbed at the intestinal level with a consequent translocation to the liver, leading, when provided solely, to sod1, sod2, and cat upregulation. Interestingly, the dietary implementation of microencapsulated AX led to a mitigation of oxidative stress. In addition, the microcapsules, due to their composition, promoted microplastic coagulation in the fish gut, limiting their absorption and accumulation in all the tissues analyzed. These results were supported by in vitro tests, which demonstrated that the microcapsules promoted microplastic coagula formation too large to be absorbed at the intestinal level and by the fact that the coagulated microplastics were released through the fish feces. [ABSTRACT FROM AUTHOR]

The cownose ray (Rhinoptera bonasus) faces vulnerability primarily due to unregulated fishing, resource overexploitation, and habitat degradation. Consequently, individuals maintained under human care play a pivotal role in species conservation, particularly when their welfare is prioritized. Achieving optimal welfare in aquarium settings relies heavily on effective management practices, notably environmental enrichment. However, research on the efficacy of such techniques for cownose rays remains limited. Thus, this study sought to evaluate the impact of various food enrichment items on the behavior of four individuals at the São Paulo Aquarium in Brazil. The project encompassed three phases: baseline, enrichment, and post-enrichment. Enrichment items, designed to mimic the species' natural foraging behavior, included an ice block containing food, food hidden in vegetables fixed to structures at the bottom of the tank, a tray with substrate and food, and a perforated plastic container with food inside. Behavioral observations utilized focal sampling with instantaneous recording every minute. Results showed increased foraging activity in the post-enrichment phase, whereas swimming increased and following behaviors decreased during the enrichment phase. Additionally, foraging behaviors predominantly occurred near the aquarium bottom. Overall, findings suggest that enrichment items effectively stimulated natural behaviors in cownose rays and were very attractive to the fish, advocating for their integration into species management protocols to enhance welfare. [ABSTRACT FROM AUTHOR]

The principles of three Rs—REPLACEMENT, REDUCTION, and REFINEMENT—govern the protection and use of animals, including fish, for research purposes in the European Union and Norway. In this paper, we discuss some straightforward steps to simplify the delivery of these principles at the idea stage and adapt some of these examples for conducting fish trials related to health and welfare. Although some of the approaches are well established in other animal science arenas, we believe there can be a timely recap of their key facets. We discuss a number of simple strategies to emphasize how a reduction in fish numbers can be achieved from initial project conception to implementation, highlighting not only their advantages but also their limitations. We also highlight the role that funding agencies can play in the implementation of the 3R principles in aquaculture research. These simple points can be used in frameworks to initiate a broader and dynamic intersectoral dialogue among stakeholders of aquaculture research on how to promote ethics and embrace opportunities for this within the tenets of the 3Rs. [ABSTRACT FROM AUTHOR]

The live transport of farmed fish is an important practice in Chinese aquaculture due to consumer preferences in its domestic market. However, live transport can be stressful for fish and may cause many welfare issues. This study aimed to examine the effects of transport density on the welfare of largemouth bass (Micropterus salmoides). Adult fish were allocated to four experimental treatments in a two‐factor design (N = 5 groups per treatment). Factor one was stocking density of either 39 (low density) or 78 (high density) g L−1. Factor two was transport, with half of the fish groups exposed to simulated transport stress for 3 h using a motion platform, and the other half kept in static tanks for the same length of time. Baseline behavior and physiology were determined from a subset of fish after acclimation but before selection into groups and application of transport. To determine the effects of transport, stocking density, and their interaction on the experimental groups, physiological sampling and behavioral recording were carried out immediately after simulated transport, and water quality was measured both before and after transport. Changes in water quality were observed between two timepoints, with decreased dissolved oxygen levels and increased water temperature. Total ammonia nitrogen levels significantly increased in all treatments over time, particularly in the high‐density groups. Fish ventilation rates were significantly elevated in the groups kept at a high stocking density regardless of whether they also experienced transport stress. Fish transported at a high stocking density also showed more fear‐related behaviors such as freezing and thigmotaxis than non‐transported groups. Serum cortisol, catalase, and aspartate transaminase levels were significantly higher in the transported treatment groups compared to the baseline fish, but no difference was found for serum glucose, lactate, and glutathione peroxidase. We concluded that 3 h of simulated transport was stressful to largemouth bass kept at 78 g L−1, as evidenced by altered fish physiological and behavioral indicators of stress, as well as deteriorated water quality. Additionally, we identified a positive correlation between serum and skin mucus samples for cortisol, glucose, and lactate in transported fish, providing important information for developing less invasive methods for the welfare assessment of largemouth bass. [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]

Fish deformities are detrimental to aquaculture and conservation initiatives; it is also an ethical problem and causes substantial financial losses to the aquaculture industry. The exact mechanism of deformities is still a mystery. Several factors cause deformities in fish; it seems that the deformations are inevitable but can be minimised by adopting good aquaculture practices such as proper broodstock husbandry, standard breeding and larval rearing protocol, management of water quality parameters, and providing nutritionally balanced feed, especially to the broodstock and developing larvae. In addition, it can be minimised by early detection of deformities, especially at the embryonic and larval stages. Monitoring of stocking materials should be an essential part of responsible aquaculture and conservation programmes; stocking materials should be free from any types of deformities as it affects not only aquaculture production, profitability and success of conservation programmes but also the reoccurrence of deformities in nature. The mechanism behind deformities and the development of low‐cost, robust methods/tools for detecting deformities in fish remain a challenge. Still, the opportunity exists to develop a robust marker that can predict deformities even at early embryonic and larval stages. [ABSTRACT FROM AUTHOR]

To investigate the possible effect of different feed ration levels on the growth, welfare, and early maturation of juvenile Atlantic salmon, 450 salmon parr with a mean (±standard error) initial weight of 51.6 g (±0.8) were reared in triplicate under three different feed ration levels for five months. The control group (100r) was fed every day, the 50r group was fed every other day, and the 33r group was fed every third day. In every group, 75 fish (half of the group) were individually tagged for monitoring of growth. The number of fin wounds was used as the welfare indicator, and to inspect the development of maturation, all fish were euthanized, and development of the gonads was monitored by visual inspection at the termination of the trial. The control group (100r) showed a significantly higher specific growth rate (0.90% day−1) compared to the lower fed groups (50r, 0.67% day−1 and 33r, 0.49% day−1); however, the growth difference was 21–24% less than expected solely on the difference in the amount of feed given to each group. The 100r group showed the highest welfare rating, and the 33r group the lowest possible, indicating more aggressive behaviour and fin biting due to feed restriction in the 33r group. No difference (p > 0.45) was found in the development of maturation in females, but the combined numbers of males in maturity stages 2–5 showed an overall trend towards slower maturation in the 33r group compared to the 100r group. Although the present findings on the development of sexual maturation were subtle due to the limited time frame of the trial, the findings offer a foundation for future investigation into the relationship between the feed ration level and the development of sexual maturation in the rearing of juvenile Atlantic salmon. [ABSTRACT FROM AUTHOR]

Ballan wrasse (Labrus bergylta) are commonly used as cleaner fish in salmon farms as a biological treatment to mitigate sea lice infestation. Improved welfare for cleaner fish both during production of these fish and when in sea-cages with salmon is crucial for the industry's development. A common operational procedure in ballan wrasse production is transporting juveniles from one landbased farm to another for further on-growing. Episodes of increased mortality have been reported after such transportations. In this study, the relationship between transport stress and post-transport mortality at the on-growing facility was examined. It was also investigated if light sedation with AQUI-S® can mitigate stress during transport. Stress was quantified by measuring cortisol release rate to the tank water during transport. This was investigated in 10 commercial live carrier truck transports (6 without AQUI-S® sedation and 4 with sedation during loading and transport). The total time of transport varied between 12 and 21h. In general, mortality was significantly higher (1.0± 0.6% day-1) the first five days posttransport compared to 15-20days post transport (0.5% day-1). There was also a strong relationship between fish weight at transport and post-transport mortality, where higher mean weight at transport reduced mortality. In contrast to what was expected, AQUI-S® treatment during transport procedures increased cortisol excretion rate, suggesting a stimulating effect of AQUI-S® on the stress axis in ballan wrasse. Considering these results, the value of using AQUI-S® to reduce stress during transport of juvenile ballan wrasse might be questioned. However, there was no relationship between cortisol release rate during transport and post-transport mortality. Furthermore, this study emphasizes that water cortisol measurements can be used as a none-invasive tool for monitoring stress and can be integrated into the welfare evaluation during commercial fish transports. [ABSTRACT FROM AUTHOR]

Simple Summary: This study focuses on the use of high-quality and sustainable feed ingredients, derived from circular bioeconomy processes, as major components of new diets for Gilthead sea bream and European sea bass, the most important farmed fish in the Mediterranean basin. In this study, we investigated the effects of replacing dietary plant proteins with insect and poultry by-product meals on the liver health of sea bream and sea bass through histological and biochemical analyses. Four diets were tested, including a control fish meal-free diet, based on plant-derived ingredients, and three other ones, in which 40% of the plant protein was replaced with Hermetia illucens and poultry by-product meals. The results revealed distinct responses to the test diets between sea bream and sea bass, in terms of biometric parameters, lipid metabolism, and liver condition. Sea bream utilized dietary nutrients efficiently, adapting to the test diets in terms of weight gain, physiological well-being, and liver health. Conversely, the test diets led to significant hepatic lipid accumulation in sea bass, resulting in an increased risk to liver health. The liver health of Gilthead sea bream and European sea bass, fed with fish meal-free diets, including various proportions of plant proteins, as well as insect and poultry by-product meals, was investigated through biochemical and histological analyses using a new liver index (LI) formula. Four isoproteic (45% Dry Matter, DM) and isolipidic (20% DM) diets were compared, including a plant-based control diet (CV) and three other test diets, in which 40% of a plant protein-rich ingredient mixture was replaced with meals from Hermetia illucens (H40) or poultry by-product (P40) alone, or in combination (H10P30). The trials lasted 12 and 18 weeks for sea bream and sea bass, respectively. The results obtained thus far highlighted species-specific differences in the physiological response to dietary changes. In sea bream, the biochemical and histological responses suggest favorable physiological and liver health statuses, with higher serum cholesterol (CHO) and triglyceride (TAG) levels, as well as moderate hepatocyte lipid accumulation, with the H10P30 diet compared to the CV (p < 0.05). In sea bass, all diets resulted in elevated serum TAG levels and lipid accumulation in the liver, particularly in fish fed the P40 one (p < 0.05), which resulted in the highest LI, coupled with a higher frequency of severe lipid accumulation, hypertrophy, cord loss, peripheral nuclei displacement, and pyknosis. In conclusion, sea bream adapted well to the test diets, whereas sea bass exhibited altered hepatic lipid metabolism leading to incipient liver steatosis, likely due to the high lipid contents of the diets, including the insect and poultry meals. The LI formula developed in this study proved to be a reliable tool for assessing the effects of dietary changes on the liver health of sea bream and sea bass, consistent with biochemical and histological findings. [ABSTRACT FROM AUTHOR]

Ensuring fish welfare is essential from the ethical, legal, environmental, economic, and social perspectives. It plays a vital role in maintaining the health and sustainability of aquaculture practices while respecting the intrinsic value and welfare of the fish themselves. The presence of reliable welfare assessment schemes is of utmost importance to appraise the well-being of animals in aquaculture and uphold stringent welfare standards. In determining fish welfare, conducting welfare assessments with non-invasive biomarkers is crucial thus the primary objective of this study is to explore the potential usability of visible parasites as welfare biomarkers in fish without causing any harm to the fish. In this research, certain secondary stress indicators (hematocrit, plasma glucose and lactate) were employed as biomarkers for assessing the well-being of European sea bass (Dicentrarchus labrax). The study aimed to investigate whether there is a possible correlation between the presence of visible ectoparasites on the gills (specifically, the Copepod parasite, Lernantropus kroyeri) and the aforementioned stress parameters. Thus, in this study, the examination was conducted to establish the validity of ectoparasites as non-invasive biomarkers for evaluating the welfare of fish. The results showed that there was a statistically significant relationship between the intensity of ectoparasites and the stress parameters used as indicators of welfare. The observable presence and intensity of ectoparasites on the gills of the fish can be proposed as a non-invasive biomarker for evaluating fish welfare in aquaculture. [ABSTRACT FROM AUTHOR]

Background: Sedative agents are utilized to mitigate stress and improve fish welfare during and after transportation. Objectives: We aimed to assess the effects of myrcene addition to the transportation water on the plasma biochemical profile of common carp, Cyprinus carpio. Methods: For this purpose, common carp (mean weight of 45.3±1.65 g) were transported in plastic bags containing myrcene at concentrations of 0 (CTL), 10 (10 M), 20 (20 M), 30 (30 M), and 50 (50 M) μL/L for 6 h. Then, their plasma parameters were compared to those values before transportation (BT). Results: Transportation significantly (P<0.05) decreased plasma total protein, albumin, alternative complement, lysozyme, sodium, and chloride, while increasing potassium, calcium, alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase in the CTL treatment, as compared to BT. Adding 50 μL/L myrcene to water prevented total plasma protein and albumin loss. Supplementing 20 μL/L myrcene to water prevented or reduced the changes in plasma ions, alanine aminotransferase, and alkaline phosphatase. Addition of 10-50 μL/L myrcene to water decreased the changes in plasma aspartate aminotransferase. Adding 20 and 30 μL/L myrcene to water mitigated the changes in plasma alternative complement, as 30 μL/L myrcene increased plasma lysozyme activity. Transportation and myrcene addition had no significant effects on plasma immunoglobulin (P>0.05). However, a significant increase was observed in plasma globulin in the 20 M treatment (P<0.05). Conclusion: In summary, adding 20 μL/L myrcene to the transport water of common carp reduced hepatic enzyme levels and improved immune parameters, and therefore, the use of myrcene improves fish welfare during transportation. [ABSTRACT FROM AUTHOR]

Cardiomyopathy syndrome (CMS) poses a significant threat to farmed Atlantic salmon (Salmo salar), leading to high mortality rates during the seawater phase. Given that controlled experimental challenge trials with PMCV do not reproduce the mortality observed in severe field outbreaks of CMS, field trials on natural CMS outbreaks are warranted. This field study explored the impact of a clinical nutrition intervention, specifically a diet enriched with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on a severe CMS outbreak in a commercial sea farm. CMS was diagnosed in a single sea cage with high mortality rates. Histopathological analysis, RT-qPCR in situ hybridization for virus detection, and fatty acid composition analysis were used to monitor the impact of disease and the inclusion of EPA and DHA in heart tissue. Following the implementation of clinical nutrition, a decline in mortality rates, regression of CMS-associated changes, and a significant reduction in piscine myocarditis virus (PMCV) RNA load were observed within the salmon population. Fatty acid composition analysis of heart samples demonstrated increased levels of EPA and DHA, reinforcing the association between dietary factors, viral load dynamics, and overall fish health. Although further validation is needed in future studies, as field trials may not be sufficient to establish causation, our results indicate that optimizing the EPA + DHA levels may prove beneficial in severe CMS outbreaks. [ABSTRACT FROM AUTHOR]

Acoustic technology has great application prospects in aquaculture. In particular, two indispensable, critical technologies for the future aquaculture industry are multi‐sensor acquisition that can achieve multi‐scale information fusion, collection and establishment of a global acoustic fish database and highly developed deep learning intelligent algorithms that can establish a correlation mechanism between fish acoustic and behaviour characteristics. Acoustic technology offers remarkable advantages in large and turbid water bodies for studying spatial and temporal distribution patterns of aquatic organism populations, developing on‐demand feeding systems and estimating biomass. This article reviews the development of acoustic technology and its application in aquaculture over the last 30 years. It further analyses, in detail, the advantages and disadvantages of acoustic technology in evaluating aquatic organism biomass and morphological and physical indicators, aquatic organism behaviour and welfare improvement. Challenges of acoustic technology in acquiring dynamic target data accurately, building a global acoustic fish database and establishing connections between fish behaviour and acoustic characteristics are also discussed. In brief, this article aims to help researchers and practitioners better understand the current state‐of‐the‐art acoustic technologies, which can provide strong support for smart aquaculture applications. [ABSTRACT FROM AUTHOR]

Assessing the potential impacts of wind farm noise on fish is a crucial aspect of Environmental Impact Assessment (EIA) studies. There is increasing evidence of disturbances and effects on hearing and behavior in animals. The black rockfish (Sebastes schlegelii) is a commercially valuable rocky reef fish native to East Asia. However, empirical studies that measure the actual consequences are lacking. In this study, we used auditory evoked potentials (AEP) to assess the effects of dominant frequency noise emitted by offshore wind farms on the auditory sensitivity, hearing threshold, swimming, and feeding behavior of juvenile black rockfish. The experimental findings revealed that the most sensitive sound frequency was 200 Hz, with the lowest hearing threshold recorded at 86.4 ± 3.4 dB re 1 mPa. Following 3 and 7 days of exposure to 200 Hz noise at 110 dB, threshold shifts in black rockfish reached 19.0 dB and 13.3 dB, respectively. During the subsequent recovery phase, these shifts decreased to approximately 9.8 dB after 3 days, respectively. The noise-exposed group exhibited higher swimming duration, moving distance, and caudal fin swing frequency compared to the control group without noise exposure. Furthermore, noise prolonged the feeding rate of black rockfish. Our findings provide the first evidence of noiseinduced temporary threshold shift and behavioral disturbances in juvenile black rockfish, implying potential fitness consequences associated with noise pollutant. [ABSTRACT FROM AUTHOR]

Simple Summary: The development of aquaculture has led to an increased attention towards the welfare of farmed fish. Transportation, a routine procedure in this industry, can be stressful for fish due to handling, air exposure, confinement, and reduced oxygen levels. Therefore, it is crucial to gain insights into optimal practices for organizing transportation, ensuring the well-being of these animals and minimizing excessive stress. The objective of this study was to assess the stress response of meagre juveniles during commercial transport from Monfalcone to Stintino (Italy), which lasted 24 h. Welfare evaluation included measuring cortisol levels in muscle and assessing the potential cellular localization of oxidative stress markers in various organs and tissues. Significant increases in cortisol were observed in the fish during transfer from housing to transport tanks and in subsequent samplings at different phases of transport. This finding suggests that either the animals had insufficient time to recover or the transport conditions were suboptimal. However, in terms of oxidative stress, overall immunohistochemical analysis did not reveal variation in marker localization before and after transport, indicating that the stress experienced by the fish during transportation might have been relatively mild. In aquaculture, the transportation of live fish is a crucial but stress-inducing practice, necessitating a thorough understanding of its impact on fish welfare. This study aimed to assess the physiological stress response of meagre (Argyrosomus regius) juveniles during a 24 h commercial transport by quantifying muscle cortisol levels using a specific radioimmunoassay. Additionally, an immunohistochemical approach was used to detect and localize the cellular distribution of oxidative-stress-related biomarkers within various tissues and organs. The results demonstrated a significant increase in muscle cortisol levels following the loading procedure, remaining elevated above basal levels throughout the 24 h transport period. This effect may be attributed to either insufficient time for recovery from the loading stress or prolonged transportation-related stress. Immunostaining for all the antibodies we examined was observed in multiple tissues and organs, but we found no notable variations among the various transport phases. In conclusion, the observed stress response appears to be mainly linked to loading stress and the transport process itself, emphasizing the importance of implementing appropriate operational procedures to safeguard fish well-being during transport. Nonetheless, the unaltered distribution of oxidative stress markers between the control and transported groups suggests that the experienced stress might be within tolerable limits. [ABSTRACT FROM AUTHOR]

This investigation aimed to assess the impact of rearing biomass on growth, digestive enzyme activity, and hematobiochemical indices of Nile tilapia in a tank-based recirculatory aquaculture system (RAS) for 90 days. Oreochromis niloticus (35.5 ± 0.24 g) were randomly stocked at the following densities: 80 fish/m3 (F80), 120 fish/m3 (F120), and 160 fish/m3 (F160) in triplicate. Ammonia, nitrate, nitrite, and CO2 were increased significantly as density increased and dissolved oxygen decreased (P < 0.05). A significantly increased weight gain, specific growth rate, growth efficiency, and protein efficiency ratio were recorded in F80 groups compared to F160 groups, whereas feed conversion ratio was decreased. Protease, amylase, and lipase activities were significantly lower as fish density increased. An improved (P < 0.05) red blood cell count, hemoglobin, and hematocrit were found in F160 groups. A considerably higher level of glucose, cortisol, triglycerides, total cholesterol, alanine, and aspartate aminotransferase were recorded in high-density tanks (P < 0.05). The crude lipid and carbohydrate contents were significantly lower in F160 groups. Hence, the outcomes of the present study indicated that stocking density 80 fish per m3 would be appropriate as it promotes the growth and health status of Nile tilapia cultured in RAS. [ABSTRACT FROM AUTHOR]

The aim of the study was to determine the influence of diets (factor D) and the time period (factor T) during which they were applied on the growth performance and physiological condition (blood plasma hematological and biochemical indicators of stress and immunity) in juvenile sea trout (Salmo trutta; initial body weight approximately 73 g). The diet of the fish that was used prior to the experiment (formulated feed; initial fish sample) was modified as follows: a different formulated feed (group B), mixed feed (feed B + prey fish; group B/N), prey fish exclusively (group N). The fish from group A were given the feed that was used prior to the beginning of the experiment. During the 28-day trial neither factors D nor T influenced absolute or relative fish growth rates. Factor D significantly influenced hematological indicators and leukograms, while the phagocytic index and cidal ability were determined by the time test (factor T). Myeloperoxidase (AMPO) was related significantly with the influence of factors D and T and also with the interaction of D×T. A significant decrease in AMPO was noted after two weeks of the test in groups B, N, and B/N, but after four weeks this indicator did not differ from that confirmed in the initial fish sample. The factors tested influenced stress indicators, i.e., cortisol (D and T) and glucose (D). Significant increases in cortisol (group B) and glucose (groups A, B, and B/N) concentrations were noted after two weeks of the test. After the subsequent two weeks (four weeks of the test) these indicators also stabilized. Sea trout from aquaculture readily accept prey fish; however, changes in diet cause stress reactions such as temporarily reduced immunity. Thus, the procedure for preparing sea trout stocking material for release, which is to change the feed from formulated to natural (live fish), should last approximately four weeks. [ABSTRACT FROM AUTHOR]

Optimizing production in aquaponics requires in‐depth knowledge of the plant, fish and microbial compartments. This opinion paper is focused on root‐released organic compounds and their implication in aquaponics, an area that has received little to no direct research to date. Key scientific literature from two distinct fields of study—phytochemicals in aquaculture science and root exudates in plant science—reveals possible pathways and effects. Root exudates, passively or actively released by plants as a stress response, protection or signalling, have the potential to influence the systems microbiome and the cultured fish, as similar phytochemicals have been found to affect bacterial abundance and diversity and fish health and behaviour. These are key aspects to run aquaponics successfully, which shows the need for further investigation to better understand sources and mechanisms of such molecules and possible ways to harness beneficial effects that can guide new research directions as the role of aquaponics grows in recirculating aquaculture. [ABSTRACT FROM AUTHOR]

Salmon lice are one of the biggest challenges to sustainable salmonid aquaculture. The species display high evolutionary potential, which is evident by its development of resistance to numerous chemical compounds used for delousing. In response to this, salmon farms now use non-chemical delousing methods to minimize the damage done by salmon lice, including heavy reliance on cleaner fish. Anecdotal reports from farmers and fish health personnel in areas where cleaner fish are used have suggested that salmon lice are becoming less pigmented, potentially making them harder for cleaner fish to visually detect. This experiment investigated changes in the pigmentation of salmon lice in relation to the use of cleaner fish, louse stage and sex, temperature, preferred salmon swimming depth, daylength, and salinity. Salmon lice were sampled from snorkel cages on a commercial salmon farm where three cages were stocked with farmed lumpfish and ballan wrasse, and three cages were without cleaner fish. Water temperature, salinity, and depth were recorded using a conductivity, temperature, and depth recorder. Pigmentation was measured via photographic analysis of individual lice. Although louse pigmentation varied considerably throughout the experiment, using cleaner fish throughout a single production cycle did not reduce average louse pigmentation compared to control cages. On average, male lice were significantly darker pigmented than females, but otherwise there were no patterns in louse pigmentation in relation to life stage, salinity, temperature, or daylength. Salmon lice exhibit a high degree of evolvability and have become resistant to every chemical removal treatment developed thus far. The present data suggest that, with the densities and species of cleaner fish commonly used in commercial salmon production, there is not strong directional selection on louse pigmentation. Lice, at least with regard to visual appearance, are not likely to adapt in a way which reduces cleaner fish efficacy anytime soon. [ABSTRACT FROM AUTHOR]

The trade of aquarium organisms is growing worldwide. This market depends on a continuous supply of healthy and colorful aquatic animals, but this sector has few initiatives. However, in the last decade, there has been a growing interest in researching captive breeding of these animals, aiming to develop a more sustainable aquarium hobby. Larviculture is an important phase in the cultivation process because the larvae are more sensitive to stress and variations in the bulk of variables, such as temperature, salinity, nutritional management, light intensity and spectrum, and environmental background colors. Because background color could be a promoter variable of proper welfare, we tested whether it affects the endocrine response of tomato clownfish Amphiprion frenatus larvae to an acute stress challenge. We show that background color influences the endocrine stress axis responsiveness in tomato clownfish. When fish were subjected to a standard acute stressor of 61 days after hatching, only fish adapted to white walls increased the whole-body cortisol levels. From the results presented herein, we recommend that white tanks be avoided for A. frenatus larviculture. Both, the less stress level and the good welfare condition of larvae reared in colored tanks may have robust, practical applications since almost all clownfish in the ornamental aquarium trade come from captive breeding. [ABSTRACT FROM AUTHOR]

Simple Summary: In this study, we evaluated welfare indicators at eight small-scale semi-intensive and intensive tilapia farms in Thailand, with a focus on four welfare categories: health, environment, behaviour, and nutrition. The results showed differences between the relative scores across all four welfare-indicator categories. Specifically, the behavioural assessments revealed poor welfare practices during the catching process on the tilapia farms, while the nutritional assessments showed differences in the feed conversion rates and K factor values. We identified correlations between the nutritional, environmental, and health indicators, which provided information about the critical welfare points in fish farming. By understanding welfare indicators and improving farming practices, farmers can produce healthier fish and improve their profits and the quality of the fish supplied to consumers. Taken together, our study provides valuable information that can be applied to the broader context of sustainable aquaculture and animal welfare. Welfare assessments have risen to prominence in the aquaculture industry, with increasing awareness of their significance among stakeholders in Thailand. In this study, we conducted a welfare assessment of tilapia (Oreochromis spp.) farms in Thailand, focusing on health, environmental, behavioural, and nutritional indicators. Comparing semi-intensive (earthen ponds) and intensive farming practices (cage culture), we found significant differences in the overall health score, particularly at farm F due to a disease outbreak (Kruskal–Wallis, p = 0.01). Skin and fin scores varied across farms, indicating their potential as indicators of tilapia health. Environmental assessments revealed differences in transparency between the two culturing systems (Mann–Whitney, p = 0.02). During the harvesting process, tilapia behaviours indicated poor welfare across all farms. However, no statistically significant difference in overall welfare scores was found between the two culturing systems. Correlations were observed between nutritional, environmental, and health indicators, with negative correlations between fish density and water transparency (r = −0.87, p = 0.02), presence of inhabitants (r = −0.78, p = 0.04), feeding behaviours (r = −0.78, p = 0.04), and swimming behaviours during capture (r = −0.98, p = 0.001). These findings provide valuable insights to enhance tilapia-farming practices and welfare in Thailand. [ABSTRACT FROM AUTHOR]

Sound has a potential impact on animal welfare and production, but the impacts of soundscapes on aquaculture species in different aquaculture production systems have been rarely studied. This study investigated the impact of varying aquaculture soundscapes on largemouth bass (Micropterus salmoides). Three soundscapes were administered to replicated tanks: Recirculating Aquaculture System (RAS:107.7 dB re 1 Pa RMS), In-Pond Raceway System (IPRS:115.1 dB re 1 Pa RMS), and Ambient (70.4 dB re 1 Pa RMS) as the control. The initial weight of fish in the three groups was 3.59 ± 0.30 g. Following a 50-day experimental period, the average weight of the Ambient group (14.08 ± 0.13 g) was significantly greater than that of the IPRS group (12.79 ± 0.08 g) (p < 0.05). Examination of physiological samples revealed that the soundscape negatively impacted the fish's immunological, anti-oxidation, and digestive enzymes. Furthermore, the external noise also influenced the locomotive patterns of the fish aggregations. Fish polarity and cohesion were significantly more discrete (p < 0.05) in both the RAS (47.79 ± 2.34° and 98.52 ± 3.22 mm) and IPRS groups (48.04 ± 0.70° and 87.70 ± 7.31 mm) compared to the Ambient group (42.76 ± 1.42° and 85.73 ± 1.57 mm). These results highlight the significant impacts of the aquaculture soundscape on the development, physiological activities, and behavioral traits of largemouth bass. Future research should focus on determining and optimizing the impact of different equipment noise to ensure optimal welfare and production performance in aquaculture systems. [ABSTRACT FROM AUTHOR]

Simple Summary: The World Organization for Animal Health recommends the use of stunning methods before the slaughter of farmed fish destined for human consumption. The use of carbon dioxide (CO2) is not recommended by the World Organisation for Animal Health for the stunning of farmed fish at pre-slaughter. However, its use continues to be common in the world. CO2 stimulates chemoreceptors, causing aversion and escape attempts when fish are immersed in CO2-saturated water. The use of CO2 in seawater with oxygenated water is allowed for pre-slaughter of halibut in Norway. Hence, there are no studies assessing loss of consciousness in halibut exposed to this stunning method. The best approach to determine unconsciousness is by measuring brain electrical activity through EEG. As fish welfare becomes a growing concern, it is important to ensure humane treatment during slaughter. This study aimed to assess the onset of unconsciousness in Atlantic halibut immersed in CO2-saturated seawater through electroencephalography (EEG). Of the 29 fish studied, 10 exhibited escape attempts, indicating aversion to CO2-saturated water despite its oxygenation. EEG signals showed four distinct phases: transitional, excitation (high amplitude–high frequency), suppressed, and iso-electric phases. The onset of the suppressed phase, indicative of unconsciousness, occurred on average 258.8 ± 46.2 s after immersion. The spectral analysis of the EEG signals showed a progressive decrease in median frequency, spectral edge frequency, and high frequency contribution, which corresponded to the gradual loss of consciousness. The study concludes that CO2-saturated water is not recommended for pre-slaughter handling of halibut due to the extended time required for the onset of unconsciousness and the observed aversive behaviour. Ensuring humane treatment during slaughter is important for addressing public concern and safeguarding fish welfare in all stages of production. [ABSTRACT FROM AUTHOR]

Medicinal plants are powerful antioxidants which can improve well-being and suppress oxidative stress caused by environmental toxins in aquatic animals. In this regard, the present research was designed to show the potential effects of psyllium (Plantago ovata) seed extract (PSE) on the growth, and immune responses of common carp Cyprinus carpio exposed to acute ammonia toxicity. To perform the study, fish were fed with diets containing 0 (T0), 0.25 (T1), 0.5 (T2), and 1% (T3) PSE for 60 days, and then exposed to ammonia (0.5 mg L−1) for 3 h. The findings showed that fish given the T1 diet outperformed the T3 and control groups in terms of ultimate weight, weight increase, and food conversion ratio. Additionally, the T1 group showed a significantly higher level of total protein and serum lysozyme activity than the other treatment groups. Moreover, the highest serum total immunoglobulin values were recorded in T1 and T2 groups. The results showed that PSE, especially at moderate levels, could successfully upregulate the transcription of immune-related genes (IFN-γ, Hsp70, TNF-ɑ, IL-1ß, IL-10, and IgE) compared to the control group after exposure to ammonia. Furthermore, improving ammonia-induced down regulations of antioxidant-related gene expressions (CYP1A, SOD, and GPX) was observed in fish fed with PSE-included diets compared to the control one. However, PSE-supplemented diets did not affect the mRNA expression level of CAT. Regarding tight junction-associated genes, the higher mRNA expression level of occludin was observed in the T1 group, whereas the downregulation of CLD3 gene occurred in all experimental groups. Conversely, significant upregulation of osmoregulation-associated gene (NKA) was recorded in all experimental groups compared to the control one. Therefore, the administration of PSE (0.25% of the diet) for 60 days is recommended to increase growth performance, improve health, and increase the resistance of common carp to oxidative stress caused by ammonia. [ABSTRACT FROM AUTHOR]

Environmental challenges related to open sea cage production of Atlantic salmon have sparked interest in developing commercial-scale semi-closed sea systems for post-smolt Atlantic salmon (100–1000 g). Determining the mass-specific water flow required by post-smolts will largely influence the design and dimensioning of such systems. In this experiment, post-smolts were exposed to four levels of specific water flow: 0.2, 0.3, 0.4, and 0.5 L kg fish−1 min−1. All treatments involved flow-through seawater with full oxygenation, a salinity of 34‰, and a mean temperature of 9.3 °C. The stocking density was kept stable at 75 kg m−3. Water pH decreased with reduced flow, while partial pressure of carbon dioxide (pCO2) and total ammonia nitrogen (TAN) in the water increased. The increase in water CO2 was reflected in the blood with increased pCO2, HCO3−, and decreased Cl− in the lowest water flow treatment (0.2 L kg fish−1 min−1), indicating a typical regulatory response to increased water CO2 over the eight-week experimental period. No negative effects on osmoregulation, external macroscopic welfare, or performance indicators were observed, suggesting that within the time period of this experiment, post-smolts can compensate for reductions in water flow down to 0.2 L kg fish−1 min−1. However, to avoid activating and exhausting potentially energy-costly physiological regulatory mechanisms, it is suggested to keep specific water flow above 0.3 L kg fish−1 min−1 in large-scale operations with semi-closed sea systems at intermediate temperatures. [ABSTRACT FROM AUTHOR]

The fish hook is a commonly known tool used in recreational fishing, which is one of the forms of active, specialised tourism. As a component of a fishing rod, the hook is intended to be anchored into the mouth of a fish and hold the fish on the end of the line while landing it. However, in the context of the protection of living aquatic resources and Catch-and-Release (C&R) fishing, its role and significance are becoming broader. In addition to the impact of the hook type on fishing efficiency, including the Catch Per Unit Effort (CPUE), the importance of hook selection in terms of minimising the resulting damage to the tissues of caught and released fish is increasing. It appears that alternative hook types, such as barbless hooks and circle hooks, are safer for fish in the aforementioned context while not significantly reducing fishing efficiency. This review study is aimed at describing the design, types, and role of the fish hook in modern C&R angling, including the impact of the hook type on both fishing efficiency and the safety and welfare of released fish, which translates into the status and protection of living aquatic resources. The issues presented in the study highlight a number of related technical, biological and social factors that are specific to inland angling in particular. Such a holistic perspective can be used to support the effective management of recreational fishing, which, as one of the most popular human activities when in contact with water, has a very significant impact on the state of the environment and, thus, on the possibility of tourism development. [ABSTRACT FROM AUTHOR]

In recent years, flathead grey mullets (Mugil cephalus) cultured in Eilat (Israel) have been highly affected by Vibrio harveyi, showing neurological signs such as uncoordinated circular swimming followed by high mortality rates. Despite the advances in and different approaches to control vibriosis associated with Vibrio harveyi, including commercial vaccines, most of them have not succeeded in long-term protection. In this study, we evaluated the effectiveness, long-term protection, and antibody production of three vaccine preparations: heat-killed bacteria (HKB), membrane proteins denaturation (BME PROT), and internal proteins (INT PROT) developed specifically against Vibrio harveyi for grey mullets. Our results show that fish immunized with heat-killed bacteria emulsified with adjuvant presented the most effective and long-lasting protection against the bacterium, and a cross-protection against other bacteria from the harveyi clade. The effectiveness of each immunization treatment correlated with the levels of specific antibody production against Vibrio harveyi in the serum of the immunized fish. [ABSTRACT FROM AUTHOR]

In Brazil, tilapia represented 57% of the total fish production. This study aimed assess the influence of different pre-slaughter methods (live chilling in ice/water (LC); anesthesia with the essential oils Ocimum americanum (OA) or Lippia alba (LA) and mechanical spiking (SP), on the meat quality parameters of Nile tilapia. The rigor mortis index showed faster onset in the LC group compared to the OA and LA groups after 3 hours. The pH value, TVB-N, and K-value remained unchanged, indicating no detrimental effects on meat quality. Mechanical spiking and essential oil anesthesia had comparable effects to live chilling. [ABSTRACT FROM AUTHOR]

In a non-linear system, such as a biological system, the change of the output (e.g., behaviour) is not proportional to the change of the input (e.g., exposure to stressors). In addition, biological systems also change over time, i.e., they are dynamic. Non-linear dynamical analyses of biological systems have revealed hidden structures and patterns of behaviour that are not discernible by classical methods. Entropy analyses can quantify their degree of predictability and the directionality of individual interactions, while fractal dimension (FD) analyses can expose patterns of behaviour within apparently random ones. The incorporation of these techniques into the architecture of precision fish farming (PFF) and intelligent aquaculture (IA) is becoming increasingly necessary to understand and predict the evolution of the status of farmed fish. This review summarizes recent works on the application of entropy and FD techniques to selected individual and collective fish behaviours influenced by the number of fish, tagging, pain, preying/feed search, fear/anxiety (and its modulation) and positive emotional contagion (the social contagion of positive emotions). Furthermore, it presents an investigation of collective and individual interactions in shoals, an exposure of the dynamics of inter-individual relationships and hierarchies, and the identification of individuals in groups. While most of the works have been carried out using model species, we believe that they have clear applications in PFF. The review ends by describing some of the major challenges in the field, two of which are, unsurprisingly, the acquisition of high-quality, reliable raw data and the construction of large, reliable databases of non-linear behavioural data for different species and farming conditions. [ABSTRACT FROM AUTHOR]

Simple Summary: Adding physical enrichment to the rearing conditions may promote fish welfare and reduce detrimental characteristics that fish develop in captivity. Senegalese sole (Solea senegalensis), an important species for European aquaculture, is reared in intensive conditions using fibreglass tanks. This species shows reproductive dysfunctions that do not allow it to complete its life cycle in production. Recently, dominance behaviour has been studied to try to solve this problem. The present study aimed to assess the effect of sand as an environmental enrichment in the dominance behaviour and brain gene expression of Senegalese sole juveniles. Several behaviours associated with feeding and territoriality were analysed by video recordings. In both environments, dominant soles were the first to feed, displayed a higher number of contact interactions and dominated the area close to the feeding point, where the events were reduced in fish maintained in the sand. The nr4a2 and fshra genes related to differentiation of dopamine neurons and regulation of maturation were significantly up-regulated in dominant fish maintained with sand compared to dominants maintained without sand. Using an enriched environment may affect Senegalese sole dominance, enhance welfare and advance future maturation. Physical complexity adds physical enrichment to rearing conditions. This enrichment promotes fish welfare and reduces detrimental characteristics that fish develop in captivity. Senegalese sole (Solea senegalensis) is an important species for European aquaculture, where it is reared in intensive conditions using fibreglass tanks. However, reproductive dysfunctions present in this species do not allow it to complete its life cycle in captivity. Recently, dominance behaviour has been studied to try to solve this problem. The present study aimed to assess the effect of sand as environmental enrichment in the dominance behaviour and brain mRNA abundance of Senegalese sole juveniles. Four tanks of sole (n = 48 fish in total) were established in two different environments (with and without sand). Juveniles were subjected to dominance tests of feeding and territoriality. Behaviours analysed by video recordings related to the distance from the food delivered and harassment behaviour towards other individuals (e.g., resting of the head on another individual). In both environments, dominant sole were the first to feed, displayed more head-resting behaviour and dominated the area close to the feeding point, where the events were reduced in fish maintained in the sand. mRNA expression related to differentiation of dopamine neurons (nr4a2) and regulation of maturation (fshra) were significantly upregulated in dominant fish in the sand environment compared to dominants maintained without sand. The use of an enriched environment may affect Senegalese sole dominance, enhance welfare and possibly advance future maturation. [ABSTRACT FROM AUTHOR]

Fish health personnel have limited tools in combatting viral diseases such as heart and skeletal muscle inflammation (HSMI) in open net-pen farmed Atlantic salmon. In this study, we aimed to predict HSMI by intensified health monitoring and apply clinical nutrition to mitigate the condition. We followed a commercial cohort (G1) of Atlantic salmon that was PRV-1 naïve when transferred to a sea cage at a location where HSMI outbreaks commonly occur. The fish in the other cages (G2-G6) at the location had a different origin than G1 and were PRV-1 positive prior to sea transfer. By continuous analysis of production data and sequentially (approximately every fourth week) performing autopsy, RT-qPCR (for PRV-1 and selected immune genes), blood and histological analysis of 10 fish from G1 and G2, we identified the time of PRV-1 infection in G1 and predicted the onset of HSMI prior to any clinical signs of disease. Identical sequences across partial genomes of PRV-1 isolates from G1 and G2 suggest the likely transfer from infected cages to G1. The isolates were grouped into a genogroup known to be of high virulence. A commercial health diet was applied during the HSMI outbreak, and the fish had low mortality and an unaffected appetite. In conclusion, we show that fish health and welfare can benefit from in-depth health monitoring. We also discuss the potential health value of clinical nutrition as a mean to mitigate HSMI. [ABSTRACT FROM AUTHOR]

While there is a growing need to increase farm fish production to meet food security needs of a growing population, humane slaughter treatments are not well understood. Use of sedative agents prior to slaughter can facilitate a more rapid and humane slaughter process. The present study was undertaken to evaluate the effects of implementing preslaughter electrosedation on the quality and consumer acceptance of farmed rainbow trout. A consumer sensory panel (n = 65) was conducted comparing rainbow trout slaughtered according to two methods: (1) immersion in an ice-water slurry (Control) or (2) immersion in an ice-water slurry immediately preceded by electrosedation (Electrosedation). Results from a sensory triangle test determined that there was no significant difference between the two fish harvested by different methods. These results suggest that electrosedation does not impact the sensory quality of farmed rainbow trout. This demonstrates that preslaughter electrosedation effectively aligns interests regarding animal welfare, efficiency, and product quality in the production of farm rainbow trout. This is an important finding as the results could provide insights for treating fish humanely without sacrificing the quality while meeting the demands of a highly regulated industry. [ABSTRACT FROM AUTHOR]

Simple Summary: Anaesthetics have been increasingly used for live fish manipulation to facilitate management, reduce stress and for welfare purposes. Plant derived natural compounds have been recommended as alternatives to synthetic drugs. Herein, juveniles of tambaqui fish, Colossoma macropomum, were exposed to geraniol and citronellol, which have been proposed as promising natural products for fish anaesthesia. The electroencephalographic response was characterised upon short-term exposure of fish to both compounds in anaesthetic concentrations, and throughout recovery in clean water. While geraniol-exposed fish showed an adequate anaesthetic effect, with depression of the central nervous system and a gradual recovery of the brain electrical activity, fish exposed to citronellol had an altered electroencephalographic response during induction, somewhat incompatible with an appropriate anaesthetic effect and smooth recovery. The aim of this study was to evaluate the level of neuronal depression in juvenile tambaqui, Colossoma macropomum, exposed to geraniol (GRL) and citronellol (CTL) in immersion baths. A total of 36 juveniles weighing 35.2 ± 9.4 g were used, organised into six experimental groups: I—control (clean water); II—ethanol (water containing the highest volume of ethanol used in the anaesthetic pre-dilution); III—GRL induction (70 µL·L−1); IV—CTL induction (90 µL·L−1); V—GRL recovery; VI—CTL recovery. Electroencephalographic (EEG) recordings were performed for 300 s in each group. EEG tracings of the control and ethanol groups showed regular and similar activity. Upon exposure to the anaesthetics, irregularities were observed in the tracings showing neuronal excitability and increased amplitudes, mainly in the case of CTL. Overall, GRL-exposed fish showed depression of the central nervous system with low and regular tracings throughout induction, presenting a gradual recovery and stable tracings, which were consistent with an adequate general anaesthetic effect. On the other hand, fish exposed to CTL showed altered EEG activity during induction, that could be considered incompatible with an appropriate anaesthetic effect and smooth recovery, presenting high and irregular EEG tracing amplitudes. [ABSTRACT FROM AUTHOR]

Knowledge about fish welfare and its impact on fish fillet quality is still insufficient. Therefore, the influence of two aspects of fish welfare (slaughtering method: bled and unbled fish; fish stock densities: 90, 120, and 150 kg·m−3) on African catfish fillet quality during postmortem conditions was investigated. The aim of study was to determine (i) the efficiency of bleeding on oxidation progress and (ii) the influence of stock density on fillet quality. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS–PAGE) showed a higher protein loss in the unbled than in the bled groups, especially in the heavy myosin chain (MHC) band. However, density did not show any influence on protein profile. Western blot analysis showed fewer oxidized carbonyls in the bled than in the unbled groups; higher oxidation development, microbial growth, and lower hardness were observed in unbled fillets. Additionally, hardness was higher at 90 and 120 kg·m−3 densities in bled fillet compared to 150 kg·m−3. The first three days of storage showed a higher oxidation rate in unbled fillets than in bled fillets, confirming the contribution of hemoglobin to oxidation development with different mechanisms of protein oxidation. The obtained results revealed the same fillet quality in all aspects at either 90 or 120 (kg·m−3) stock densities, which would suggest 120 kg·m−3 for the fishery industry. However, higher stocking density in this study would not be appropriate for fish welfare. [ABSTRACT FROM AUTHOR]

The study of the molecular mechanisms of stress appraisal on farmed fish is paramount to ensuring a sustainable aquaculture. Stress exposure can either culminate in the organism's adaptation or aggravate into a metabolic shutdown, characterized by irreversible cellular damage and deleterious effects on fish performance, welfare, and survival. Multiomics can improve our understanding of the complex stressed phenotype in fish and the molecular mediators that regulate the underlying processes of the molecular stress response. We profiled the stress proteome and metabolome of Sparus aurata responding to different challenges common to aquaculture production, characterizing the disturbed pathways in the fish liver, i.e., the central organ in mounting the stress response. Label-free shotgun proteomics and untargeted metabolomics analyses identified 1738 proteins and 120 metabolites, separately. Mass spectrometry data have been made fully accessible via ProteomeXchange, with the identifier PXD036392, and via MetaboLights, with the identifier MTBLS5940. Integrative multivariate statistical analysis, performed with data integration analysis for biomarker discovery using latent components (DIABLO), depicted the 10 most-relevant features. Functional analysis of these selected features revealed an intricate network of regulatory components, modulating different signaling pathways related to cellular stress, e.g., the mTORC1 pathway, the unfolded protein response, endocytosis, and autophagy to different extents according to the stress nature. These results shed light on the dynamics and extent of this species' metabolic reprogramming under chronic stress, supporting future studies on stress markers' discovery and fish welfare research. [ABSTRACT FROM AUTHOR]

Simple Summary: Every year an estimated 1.5–2.7 billion wild fish are caught by UK commercial sea fishing fleets subjecting most to severe stressors. Scientific research shows that fish are sentient beings, but UK animal welfare laws do not protect commercially caught wild fish. For example, stunning fish before slaughter is rare and gutting them alive is a common practice. There are therefore major welfare issues in wild capture sea fisheries, no laws to protect the welfare of wild fish at sea, and great potential to reform practice to improve the lives of billions of sentient fish. The article investigates this through reporting findings from interviews with 18 experts with a stake in wild fish welfare. The article reviews the UK fishing industry, policy context and scientific evidence that fish are sentient, linked to stakeholder views about what fish experience during wild capture. The article then analyses industry practices, resultant welfare harms and stakeholder attitudes towards them. No participant disputed that fish are sentient and all were able to identify key stressors to fish in different stages of the capture process, together with potential mitigations. Interviews revealed that harms can be worsened by their hidden nature along with conservative industry attitudes towards brutal practices which would be unacceptable in other areas of animal food production. The article raises awareness of an under-researched welfare problem in UK wild capture sea fisheries but should have wider significance to many fishing nations. An estimated 1.5–2.7 billion wild fish are caught by UK commercial sea fishing fleets annually. Most are subjected to severe stressors during capture; stunning is rare and gutting alive is common practice. Fish are recognised in UK law as sentient beings, but commercially caught wild fish are excluded from welfare protections. Animal welfare impacts in wild capture sea fisheries are therefore on a massive scale, with major potential for legislative and market-based reforms. Interviews were conducted with 18 experts working within the fishing and seafood industry, fisheries management, scientific research and animal/fish advocacy organisations. The findings reveal a significant welfare gap between societally acceptable ways to treat sentient animals and the reality of capture fisheries. The participants pointed to harms caused to fish throughout different stages of the capture process caused by combinations of variables from fishing gear and methods to biological, environmental and other factors, noting that all require mitigation. Interviews revealed that the nature of harms may be exacerbated by conservative attitudes towards brutal practices in the industry, driven by profit and efficiency and free from legal restraint. To address the welfare gap, stakeholders favour engagement with the industry to improve understanding of harms and to identify mutually beneficial and shared objectives through alleviating stressors to fish in the capture process. This empirical research is focused on UK wild capture sea fisheries. However, given the dearth of welfare legislation globally, it has significance for fishing nations and the many billions of wild sea fish captured each year around the world. [ABSTRACT FROM AUTHOR]