Fish Welfare Research Articles

Zebrafish Nutrition: Promoting Fish Health and Welfare of the Animal Model in Halal Science Research

Zebrafish (Danio rerio) is a popular animal model in a variety of fields, including molecular biology, neurology, genetic research, aquaculture, and even halal science research. As the use of zebrafish in research grows, so does the need to focus on their welfare to ensure that they live in normal-good health, fit for research. Nutrition is an important but often overlooked welfare factor in zebrafish, as it affects their development, health, reproduction, and response to stimuli. In many modern laboratory settings, zebrafish feeding is dependent on the researcher, with numerous types of feed and feeding regimens used without a rigorous assessment of the fish growth. This is largely owing to a lack of information about zebrafish nutritional requirements, which is regarded as the most fundamental fault in any nutritional and growth study. A standard fish diet with an adequate amount of nutrition including the appropriate ratio of protein, carbohydrate, lipids, vitamins, and minerals are proposed to prevent the unplanned nutritional effect to the outcomes of such experiments. Protein is important for the growth of the fish while carbohydrates and lipid are the non-protein source of dietary energy for the fish diet. Feeds with the proper amount of dietary ingredients can help the fish live at optimum health. Islam teaches zero-tolerance to all forms of animal abuse throughout the halal production supply chain and although not many, there is a few number of demands on animal welfare as a purchase criterion. Therefore, as far as halal science is concerned, care must be taken to ensure the protection and welfare of laboratory animals utilized in research.

Assessing Stress Resilience After Smolt Transportation by Waterborne Cortisol and Feeding Behavior in a Commercial Atlantic Salmon (Salmo salar) Grow-Out Recirculating Aquaculture System.

Sampling protocols and water quality sensors have been developed to assess fish health and welfare in recirculating aquaculture systems (RASs). Still, the use of fish-based non-invasive welfare indicators, reflecting the physiological state of the fish, is limited in this type of system. Cortisol, the major stress-coping hormone in fish, diffuses through the gills. Consequently, waterborne cortisol is a potential fish-based non-invasive welfare indicator in RAS. However, its use in commercial rearing systems is sparse. In this study, we evaluated water cortisol levels and feeding behavior as welfare indicators of newly inserted smolt in a commercial RAS for harvest size Atlantic salmon. The RAS consisted of two parallel fish rearing raceways, raceways 1 and 2, sharing the same water treatment with common outlets and inlets. The smolts were inserted in raceway 1 while salmon that have been in the system for 6 months or more were kept in raceway 2. The smolt insertion period was 3 days. Samples for water cortisol levels were withdrawn the day before, 1 and 3 days after the smolt insertion period. Smolt insertion resulted in elevated water cortisol concentrations in the entire system, with the highest values in raceway 1, one day after smolt insertion. Estimated cortisol production in newly inserted smolt decreased over time, was similar to what has been reported in salmon adapting to experimental tanks. Feeding behavior indicated that the appetite was not fully resumed in the newly inserted smolts, while the appetite of fish in raceway 2 was unaffected by smolt insertion. These results, obtained in a highly intensive commercial RAS, suggest that waterborne cortisol together with feeding behavior can be used as indicators for adaptive processes associated with stress resilience in farmed fish. Thus, they are promising non-invasive indicators for assessing the impact of potential stressors on fish welfare in this type of rearing system.

Research Before Policy: Identifying Gaps in Salmonid Welfare Research That Require Further Study to Inform Evidence-Based Aquaculture Guidelines in Canada.

Aquaculture is a growing industry worldwide and Canadian finfish culture is dominated by marine salmonid farming. In part due to increasing public and stakeholder concerns around fish welfare protection, the first-ever Canadian Code of Practice for the Care and Handling of Farmed Salmonids was recently completed, following the National Farm Animal Care Council's (NFACC) rigorous Code development process. During this process, both the Scientific (responsible for reviewing existing literature and producing a peer-reviewed report that informs the Code) and Code Development (a diverse group of stakeholders including aquaculture producers, fish transporters, aquaculture veterinarians, animal welfare advocates, food retailers, government, and researchers) Committees identified research gaps in tandem, as they worked through the literature on salmonid physiology, health, husbandry, and welfare. When those lists are combined with the results of a public “top-of-mind” survey conducted by NFACC, they reveal several overlapping areas of scientific, stakeholder, and public concern where scientific evidence is currently lacking: (1) biodensity; (2) health monitoring and management, with a focus on sea lice infection prevention and management; (3) feed quality and management, particularly whether feed restriction or deprivation has consequences for welfare; (4) enclosure design, especially focused on environmental enrichment provision and lighting design; and (5) slaughter and euthanasia. For each of these five research areas, we provide a brief overview of current research on the topic and outline the specific research gaps present. The final section of this review identifies future research avenues that will help address these research gaps, including using existing paradigms developed by terrestrial animal welfare researchers, developing novel methods for assessing fish welfare, and the validation of new salmonid welfare indices. We conclude that there is no dearth of relevant research to be done in the realm of farmed salmonid welfare that can support crucial evidence-based fish welfare policy development.

Evaluation of six methods for external attachment of electronic tags to fish: assessment of tag retention, growth and fish welfare.

External attachment of electronic tags has been increasingly used in fish studies. Many researchers have used ad hoc attachment methods and provided little or no validation for the assumption that tagging itself does not bias animal behaviour or survival. The authors compared six previously published methods for externally attaching acoustic transmitters to fish in a tank holding experiment with black sea bass Centropristis striata (L.). They tracked tag retention, fish growth and external trauma (as a measure of fish welfare) for 60 days. For each of these metrics, the results showed a wide range of responses among tagging treatments. A simple attachment method using a spaghetti tag passed through the dorsal musculature of the fish and tied to the end cap of the transmitter emerged as the preferred option based on high retention, no impact on growth and relatively low detriment to fish welfare. Future field studies using external electronic tagging should consider tag‐related effects that could compromise results when selecting a method for tag attachment.

Bioprocessing post‐consumer food waste for use as a fish feed ingredient

Post-consumer food waste (FW) is a sustainable source of nutrients that could be used as aquafeed ingredient to decrease aquaculture production expenses. However, FW has a relatively low protein content. Bioprocessing can help improve the nutritional composition of FW prior to using it in aquafeed. The present study assessed the potential benefits of substituting part of juvenile Nile tilapia (Oreochromis niloticus) diets with yeast-fermented oil-extracted FW (FWY). Seven isonitrogenous diets (34% crude protein) were prepared, replacing the standard formulation with 0, 15, 20, 25, 30, 35 and 40% FWY. Juvenile O. niloticus (11.07 ± 0.01 g) were size sorted and stocked into 21 tanks. Each diet was randomly assigned to three replicate tanks, and fish were offered their respective diets for 6 weeks. Results suggest that up to 30% of Nile tilapia feed can be substituted with FWY without significant effect on final body weights and lengths, feed conversion ratio, specific growth rate, hepatosomatic and viscerosomatic indices, body moisture, protein and lipid content of fish. Using an inexpensive ingredient such as FWY to replace 30% of traditional aquafeed ingredients is a promising approach towards decreasing aquaculture production cost without compromising fish growth and welfare.

Effects of simple shelters on growth performance and welfare of rainbow trout juveniles

Environmental enrichment is a promising strategy to improve the welfare of fish in captivity. However, the utilization of enrichment in aquaculture is still infrequent, maybe because there is a paucity of knowledge about how its effects depend on factors such as fish species, developmental stage, social environment or the type and extent of enrichment. In this study, we evaluated the effects of physical enrichment on the welfare of rainbow trout juveniles, by exposing them to simple plastic screen shelters. Juveniles of approx. 15 g were introduced to two types of submerged shelters: full screens (Full) or partial screens (Semi), and fish welfare was assessed and compared to a control group (without shelters) by evaluating fish growth and condition, extent of external lesions, and the neuroendocrine responses to acute and repeated stress. During the eleven-week experimental period, the fish in the sheltered units gradually developed a clear shelter-seeking behavior when exposed to external disturbance. Fish growth, condition factor and mortality were not affected by shelter presence. The presence of full shelters had a modest protective effect on fin damage: both pectoral fin- and total fin damage scores were reduced (> 10%) in this group with respect to the control group; the percentage of fish with severe damage in the pectoral fin was reduced in the Full group with respect to the Control (63% vs 82%). Partial shelters had no significant effect on fin damage scores, when compared to the control group. The presence of shelters did not affect the general level of stress upon standardized acute or repeated stressors. However, fish used to the presence of shelters showed a more intense startling response when exposed to stressors that forced them to abandon the shelter protection. Altogether, this study shows potential for shelters to be used as a welfare-promoting strategy in trout farming, but further research is needed to optimize the shelter type and design and the proper timing for its application.

Dynamic feeding method for aquaculture fish using multi-task neural network

In recirculating aquaculture system (RAS), fish feeding is the most important part in production management, which is not only related to economic benefits, but also the key to ensure fish welfare and increase production. At present, in RAS, fish are basically fed either artificially or automatically (quantitatively supply feed at definite time), which can easily result in under-feeding or over-feeding of fish. Therefore, there is an urgent to develop an intelligent method that realizes appropriate feeding according to the actual demands of fish. This research attempts to explore a fish dynamic feeding method based on the multi-task network to meet the automatic adjustment of both the feeding intervals (the time intervals between feeding points in repeated feeding in a single-round) and feeding rates. The specific objectives of this study include two parts: 1) to construct a multi-task network to analyze the feeding activity of cultured fish and monitor the amount of uneaten feed pellets; 2) to design a feeding strategy based on information obtained from the multi-task network that realizes the dynamic adjustment of feeding intervals and the decision of feeding endpoint. The waste of feed pellets can be reduced by dynamically adjusting the feeding intervals, and the under-feeding and over-feeding of fish can be prevented by determining feeding endpoint. The results indicated that the accuracy of feeding activity classification by multi-task network reached 95.44%, and the mean absolute error (MAE) and mean square error (MSE) in uneaten feed pellet counting were 4.80 and 6.75, which indicate that the multi-task network can accurately monitor the fish feeding activity and the amount of uneaten feed pellets. Based on the two monitored information, combined with the feeding strategy, we dynamically adjusted the feeding intervals and determined the feeding endpoint, and then compared the feeding endpoints with manual judgment to verify the feasibility and accuracy of the dynamic feeding method based on the multi-task network. In summary, this research provides a more accurate and efficient solution for the intelligent and precise feeding of cultured fish, and provides the theoretical foundation for the development of intelligent feeding devices.

Intermittent administration of peracetic acid is a mild environmental stressor that elicits mucosal and systemic adaptive responses from Atlantic salmon post-smolts

BackgroundFish encounter oxidative stress several times during their lifetime, and it has a pervasive influence on their health and welfare. One of the triggers of oxidative stress in fish farming is the use of oxidative disinfectants to improve rearing conditions, especially in production systems employing recirculation technology. Here we report the physiological and morphological adaptive responses of Atlantic salmon (Salmo salar L.) post-smolts to intermittent exposure to a potent oxidative agent peracetic acid (PAA). Fish reared in semi-commercial scale brackish water recirculating aquaculture system (RAS) were exposed to 1 ppm PAA every 3 days over 6 weeks. Mucosal and systemic responses were profiled before exposure, 22 and 45 days during the intermittent PAA administration.ResultsOxidative stress was likely triggered as plasma antioxidant capacity increased significantly during the exposure period. Adaptive stress response to the periodic oxidant challenge was likewise demonstrated in the changes in plasma glucose and lactate levels. PAA-induced alterations in the transcription of antioxidants, cytokines, heat shock proteins and mucin genes showed a tissue-specific pattern: downregulation was observed in the gills and olfactory rosette, upregulation occurred in the skin, and no substantial changes in the liver. Further, PAA exposure resulted in histological changes in key mucosal organs (i.e. olfactory rosette, skin and gills); pathological alterations were predominant in the gills where cases of epithelial lifting, hypertrophy and clubbing were prevalent. In addition, intermittent PAA administration resulted in an apparent overproduction of mucus in the nasal mucosa. Lastly, PAA did not dramatically alter the ability of salmon to mount a physiological stress response in the presence of a secondary stressor, though some subtle interference was documented in the kinetics and magnitude of plasma cortisol and glucose response post-stress.ConclusionsThe present study collectively demonstrated that intermittent oxidant exposure was a mild environmental stressor that salmon could mount strong adaptive responses at systemic and mucosal levels. The results will be valuable in optimising the rearing conditions of post-smolts in RAS, especially in adopting water treatment strategies that do not considerably interfere with fish health and welfare.

Influence of diet and feeding strategy on the performance of nitrifying trickling filter, oxygen consumption and ammonia excretion of gilthead sea bream (Sparus aurata) raised in recirculating aquaculture systems

Gilthead sea bream (Sparus aurata) was raised in six individual recirculating aquaculture systems (RAS) whose biofilters’ performance was analyzed. Fish were fed with three different diets (a control diet, a fishmeal-based diet (FM), and a plant meal-based diet (VM)) and with three different feeding strategies (manual feeding to apparent satiation, automatic feeding with restricted ration, and auto-demand feeding). For every combination of diet and feeding strategy, the mean oxygen consumption, ammonia excretion, and ammonia removal rate were determined. Fish fed with the VM diet consumed the most oxygen (20.06 ± 1.80 gO2 consumed kg−1 day−1). There were significant differences in ammonia excretion depending on the protein content and protein efficiency of the diet, as well as depending on feeding strategy, which in turn affected ammonia removal rates. Fish fed by auto-demand feeders led to the highest mean ammonia removal rate (0.10 gN-TAN removed m−2 biofiltration area day−1), while not leading to peaks of high ammonia concentration in water, which preserve fish welfare and growth.

Fish welfare in Ukraine

Fish welfare is a very important aquaculture criterion that is affected by various factors. In Ukraine, fish welfare is unregulated, except for certain aspects of fish keeping, fishing rules and sanitation requirements. In general, legislation is too general and concise. Therefore, we carried out a study on several critical aspects of fish welfare in Ukraine: 1) fish farming management, 2) environmental factors and parameters of the aquatic environment in fish farming, 3) staff, 4) feeding, 5) fish behaviour and stocking density, 6) fish health, 7) impact of stressors on fish reproduction, and 8) antimicrobial resistance. The analysis shows problems in specialized fish farms, such as non-compliance with rearing technology, lack of quality feed and high feed cost. Analysis of the epizootic situation regarding fish diseases during the last 10 years shows that invasive and infectious diseases are recorded in almost all fishpond farms. Nosological profile pathogens were bacteria of genera Aeromonas (40%), Pseudomonas (28%), and Edwardsiella, Proteus, Yersinia, Flavobacterium, and Micrococcus (all five accounting for 32%). Analysis of the state of welfare indicates the need to develop an evaluation system of fish welfare and its implementation in Ukraine. We consider that it is necessary to develop an algorithm for implementing the best practices of fish welfare based on assessment and research, improvement of legal framework, and implementation of effective programmes for the control of aquatic animal welfare.

Sentience politics : a fishy perspective

The plight of fishes has almost certainly got worse since Bentham (1789) coined the phrase “The question is not Can they reason? nor, Can they talk? but Can they suffer?” Despite the fact that fishes are increasingly recognised as sentient animals worthy of protection under animal welfare legislation in many countries around the world, fishing practices are almost universally exempt activities. The human population continues to grow, and, surprisingly, per capita intake of fish is still increasing (FAO 2020). The source of this fish is not wild stocks (catches of which have remained more or less stagnant for decades after we pillaged the oceans), but rather from a huge increase in aquaculture production. Aquaculture is currently experiencing a rapid industrialisation phase reminiscent of that seen in terrestrial food production systems over the last century. There is an urgent need for the animal welfare developments of the past 50 years that were established for terrestrial food production systems to be applied to aquaculture. Given these facts, one alarming question presents itself: Who is looking after the welfare of fishes in the context of commercial fishing and aquaculture?

Motion trajectory estimation of salmon using stereo vision

A main concern for the aquaculture industry is the fish behaviour and welfare. Motion trajectory analysis of salmon at aquaculture farming sites with respect to certain aquaculture operations aims to provide information about the behaviour and possibly stress level of the farmed salmon and may help to generate a general welfare indicator index. Towards this aim we present an innovative computer vision and machine learning based approach for motion trajectory estimation of salmon. Video footage was recorded with a stereo camera setup. Deep learning based object detection was performed to detect particular features. We focused on tracking the fish eyes and heads as a reliable indicators of the fish's position. Feature matching and subsequent 3D reconstruction was performed to calculate the 3D position of the fish from which trajectories of the fish movement were estimated. Related experiments were conducted at an aquaculture research facility under natural lighting conditions and extracted trajectories allowed a qualitative verification. The developed method was verified using synthetic ground truth data produced with an open source computer graphics software for quantifiable performance metrics.

A Method Based on Knowledge Distillation for Fish School Stress State Recognition in Intensive Aquaculture

Fish behavior analysis for recognizing stress is very important for fish welfare and production management in aquaculture. Recent advances have been made in fish behavior analysis based on deep learning. However, most existing methods with top performance rely on considerable memory and computational resources, which is impractical in the real-world scenario. In order to overcome the limitations of these methods, a new method based on knowledge distillation is proposed to identify the stress states of fish schools. The knowledge distillation architecture transfers additional inter-class information via a mixed relative loss function, and it forces a lightweight network (GhostNet) to mimic the soft probabilities output of a well-trained fish stress state recognition network (ResNeXt101). The fish school stress state recognition model's accuracy is improved from 94.17% to 98.12% benefiting from the method. The proposed model has about 5.18 M parameters and requires 0.15 G FLOPs (floating-point operations) to process an image of size 224 × 224. Furthermore, fish behavior images are collected in a land-based factory, and a dataset is constructed and extended through flip, rotation, and color jitter augmentation techniques. The proposed method is also compared with other state-of-the-art methods. The experimental results show that the proposed model is more suitable for deployment on resource-constrained devices or real-time applications, and it is conducive for real-time monitoring of fish behavior.

Genomic Epidemiology of Salmonid Alphavirus in Norwegian Aquaculture Reveals Recent Subtype-2 Transmission Dynamics and Novel Subtype-3 Lineages.

Viral disease poses a major barrier to sustainable aquaculture, with outbreaks causing large economic losses and growing concerns for fish welfare. Genomic epidemiology can support disease control by providing rapid inferences on viral evolution and disease transmission. In this study, genomic epidemiology was used to investigate salmonid alphavirus (SAV), the causative agent of pancreas disease (PD) in Atlantic salmon. Our aim was to reconstruct SAV subtype-2 (SAV2) diversity and transmission dynamics in recent Norwegian aquaculture, including the origin of SAV2 in regions where this subtype is not tolerated under current legislation. Using nanopore sequencing, we captured ~90% of the SAV2 genome for n = 68 field isolates from 10 aquaculture production regions sampled between 2018 and 2020. Using time-calibrated phylogenetics, we infer that, following its introduction to Norway around 2010, SAV2 split into two clades (SAV2a and 2b) around 2013. While co-present at the same sites near the boundary of Møre og Romsdal and Trøndelag, SAV2a and 2b were generally detected in non-overlapping locations at more Southern and Northern latitudes, respectively. We provide evidence for recent SAV2 transmission over large distances, revealing a strong connection between Møre og Romsdal and SAV2 detected in 2019/20 in Rogaland. We also demonstrate separate introductions of SAV2a and 2b outside the SAV2 zone in Sognefjorden (Vestland), connected to samples from Møre og Romsdal and Trøndelag, respectively, and a likely 100 km Northward transmission of SAV2b within Trøndelag. Finally, we recovered genomes of SAV2a and SAV3 co-infecting single fish in Rogaland, involving novel SAV3 lineages that diverged from previously characterized strains >25 years ago. Overall, this study demonstrates useful applications of genomic epidemiology for tracking viral disease spread in aquaculture.

Crowding stress-related protein markers: New candidates for assessing welfare of largemouth bass reared in an in-pond raceway system

Compared to traditional pond culture, in-pond raceway system (IPRS) is an advanced model, which can reduce waste of water resources and have the characteristics of high efficiency, high yield and environmental protection. However, how to determine the appropriate stocking density has not been studied using protein markers, especially from a welfare perspective. Therefore, this study mainly evaluated the effect of stocking density on the growth, meat quality and liver proteome of largemouth bass (Micropterus salmoides). Largemouth bass (average weight, 14.29 ± 0.26 g) were randomly distributed into three in-pond raceways at three stocking densities: low stocking-density (LSD, 7000 individual/raceway), medium stocking-density (MSD, 20,000 individual/raceway) and high stocking-density (HSD, 30,000 individual/raceway). The growth performance, muscle quality and liver protein expression were analyzed after a 58-day feeding trial. The results showed that the LSD group obtained significantly higher specific growth rate compared to the HSD group. As the density increased, the survival rate of fish decreased from 92.56% to 86.33%, and the feed conversion ratio increased from 1.21 to 1.45. Different stocking densities can significantly affect the contents of essential fatty acids in muscle, but not have any obvious changes on the amino acid pattern in muscle. A total of 109, 35 and 209 differentially regulated liver proteins were detected in LSD vs. MSD, MSD vs. HSD, and HSD vs. LSD groups, respectively. Among them, Hsp70, Grp78, Erp57, Gfpt1, Pyg and Acc1 are involved in stress, glucose metabolism or lipid metabolism, which were confirmed by western blotting. Thus, these proteins could be selected as biomarkers to determine stocking density. The findings will benefit IPRS to balance the yield and welfare of fish according to the market and law changes, beyond profit-seeking in the future.

Effects of the 5-HT1A receptor agonist 8-OH-DPAT on aggressive behavior in juvenile pufferfish, Takifugu rubripes.

Severe aggressive behavior of juvenile pufferfish affects economic efficiency and fish welfare in aquaculture. 5-HT plays an important role in regulating the aggressive behavior of fish in aquaculture environment. This study examined the effects of different concentrations (0, 0.25, 0.5, 1 mg/kg) of 8-OH-DPAT, a selective 5-HT1A receptor agonist, on the aggressive behavior of juvenile pufferfish. Forty-five minutes after drug injection, the aggressive behavior of juvenile fish was recorded for 20 min, including the latency to the first attack and the frequency of aggressive behaviors. The results showed no significant differences in the latency to the first attack of juvenile fish among treatment groups. During the first 10 min of the observation period, there was no significant difference in the total aggressive acts and locomotor activity among treatment groups. Total aggressive acts and locomotor activity were the least in the 1 mg/kg 8-OH-DPAT-treated during the 20 min observation period. Both aggressive behavior and locomotor activity were negatively correlated with 8-OH-DPAT treatment overall, respectively. The above results suggested that the serotonergic system activation had suppressive effects on aggressive behavior and locomotor activity in juvenile pufferfish.

Tracking and Analysis of the Movement Behavior of European Seabass (Dicentrarchus labrax) in Aquaculture Systems

Monitoring and understanding fish behavior is crucial for achieving precision in everyday husbandry practices (i.e. for optimizing farm performance), and for improving fish welfare in aquaculture. Various intelligent monitoring and control methods, using mathematical models, acoustic methods and computer vision, have been recently developed for this reason. Here, a tracking algorithm based on computer vision that extracts short trajectories of individual European seabass in both recirculating aquaculture systems and sea cages was developed using videos from network cameras. Using this methodology, parameters such as instantaneous normalized speed, travel direction and preference for the tank surface by European seabass could be quantified. When testing the sensitivity of this algorithm for detecting fish swimming variations under different husbandry scenarios, we found that the algorithm could detect variations in all of the abovementioned parameters and could potentially be a useful tool for monitoring the behavioral state of European seabass.

Boldness Predicts Aggressiveness, Metabolism, and Activity in Black Rockfish Sebastes schlegelii

Animal personality refers to individual behavioral and physiological differences that are consistent over time and across context. Recently, the fish personality has gained increasing attention, especially from the perspective of aquaculture production. Here, we used an important aquaculture species, black rockfishSebastes schlegelii, as the target animal, and conducted a series of experiments to explore the relationships among fish boldness, aggressiveness, locomotor activity, opercular beat rate, standard metabolic rate, and cortisol level. Generally, the results showed that the boldness of black rockfish was significantly, positively correlated with fish aggressiveness, stressed locomotor activity, and standard metabolic rate, while was negatively correlated with stressed opercular beat rate. Bold fish had significantly higher aggressiveness, standard metabolic rate, and stressed locomotor activity but lower stressed opercular beat rate. However, there were no significant correlations between boldness and basal locomotor activity or between boldness and basal cortisol level. These results preliminarily constructed the behavioral and physiological spectrum of black rockfish in the context of fish personality and clearly indicated that the boldness could be used as a discrimination tool to predict fish aggressiveness and metabolic rate, which may have valuable applications for decreasing fish harmful aggression and increasing fish welfare in the aquaculture industry.

Sentinels in Salmon Aquaculture: Heart Rates Across Seasons and During Crowding Events.

Advances in tag technology now make it possible to monitor the behavior of small groups of individual fish as bioindicators of population wellbeing in commercial aquaculture settings. For example, tags may detect unusual patterns in fish heart rate, which could serve as an early indicator of whether fish health or welfare is becoming compromised. Here, we investigated the use of commercially available heart rate biologgers implanted into 24 Atlantic salmon weighing 3.6 ± 0.8 kg (mean ± SD) to monitor fish over 5 months in a standard 12 m × 12 m square sea cage containing ∼6,000 conspecifics. Post tagging, fish established a diurnal heart rate rhythm within 24 h, which stabilized after 4 days. Whilst the registered tagged fish mortality over the trial period was 0%, only 75% of tagged fish were recaptured at harvest, resulting in an unexplained tag loss rate of 25%. After 5 months, tagged fish were approximately 20% lighter and 8% shorter, but of the similar condition when compared to untagged fish. Distinct diurnal heart rate patterns were observed and changed with seasonal day length of natural illumination. Fish exhibited lower heart rates at night [winter 39 ± 0.2 beats per min (bpm), spring 37 ± 0.2 bpm, summer 43 ± 0.3 bpm, mean ± SE] than during the day (winter 50 ± 0.3 bpm, spring 48 ± 0.2 bpm, summer 49 ± 0.2 bpm) with the difference between night and day heart rates near half during the summer (6 bpm) compared to winter and spring (both 11 bpm). When fish experienced moderate and severe crowding events in early summer, the highest hourly heart rates reached 60 ± 2.5 bpm and 72 ± 2.4 bpm, respectively, on the day of crowding. Here, if the negative sublethal effects on fish that carry tags (e.g., growth rate) can be substantially reduced, the ability to monitor diurnal heart rate patterns across seasons and detect changes during crowding events, and using heart rate biologgers could be a useful warning mechanism for detecting sudden changes in fish behavior in sea cages.

Real-time detection and tracking of fish abnormal behavior based on improved YOLOV5 and SiamRPN++

In recirculating aquaculture system, the abnormal behavior of fish is usually caused by poor water quality, hypoxia or diseases. Delayed recognition of this behavior will lead to large number of fish deaths. Thus, real-time detection and tracking of fish that behaviors abnormally is an effective way to promote the fish welfare and to improve the survival rate as well as economic benefits of aquaculture. However, due to the high-density breeding, the targets in the fish images are often quite small and in occlusion, which causes high false detection and target loss rate. This article proposes a combined end-to-end neural network to detect and track the abnormal behavior of porphyry seabream. The detection algorithm passes the initial value of the target into the tracking algorithm, and the tracking algorithm tracks subsequent frames to achieve end-to-end abnormal fish behavior detection and achieve high-speed and accurate tracking of abnormal behavior individuals.In the target detection part, YOLOV5s is improved by incorporating multi-level features and adding feature mapping. Compared with the original network, the detection precision AP50:95 is increased by 8.8% while AP50 reaches 99.4%. In the target tracking part, this paper achieves multi-target tracking of abnormal fish based on single-target tracking algorithm SiamRPN++. The tracking precision is 76.7%. By combining the two approaches, individual fish with abnormal behavior can be detected precisely and tracked in real time.