Fish Welfare Research Articles

Biomarkers in Skin Mucus for a Minimally Invasive Approach to Stress in Red Tilapia (Oreochromis sp.) Fry

In a context where aquaculture continues to grow, it is essential to understand how culture conditions influence fish stress. The welfare of red tilapia fry (Oreochromis sp.), weighing 0.6 ± 0.3 g and with an initial total length of 3.548 ± 0.285 cm, was evaluated in two culture systems, biofloc and land-based ponds, over a period of 30 days through biomarkers associated with the skin mucosa, such as protein, glucose, lactate, and the hormone cortisol, in addition to their relationships with protein, seeking a comprehensive view of the physiological state and stress of these fish. Mucus samples were thawed and prepared by mechanical homogenization and centrifugation. The results reveal that the biofloc system provides a more conducive environment for welfare, evidenced by higher mucus protein levels of 1.598 ± 0.733 mg/mL, 2.316 ± 1.01 mg/mL, and 1.203 ± 0.640 mg/mL for culture days 10, 20 and 30, respectively, and lower cortisol > 1 ng/mL and lactate contents 1799 ± 1135 µg/mL, 30,271 ± 24,613 µg/mL, and 21,829 ± 23,507 µg/mL for culture days 10, 20 and 30, respectively, compounds largely associated with animal stress. This highlights the direct relationship between culture, environment and fish health and highlights skin mucus as a valuable minimally invasive biomarker. It is also important to note that improved fish welfare supports fish growth and health and promotes more sustainable aquaculture practices, contributing to more efficient and responsible production in the industry.

Ornamental fish ownership in New Zealand: Attitudes toward veterinary care and welfare considerations

This study describes ornamental fish ownership in Aotearoa / New Zealand, focusing on attitudes towards veterinary care and fish welfare. With 9% of households here and 12% in Australia having aquariums with up to eight fish, knowledge of fish husbandry and ability to provide for welfare are important considerations in a growing industry. Utilising an online survey of 58 respondents, the study findings indicate that while fish owners exhibit greater knowledge of fish care compared to non-owners, there is a difference in the perceived value of fish in comparison to other pets such as cats and dogs. Respondents with fish are more likely to seek information from non-veterinary sources due to limited availability of specialised fish veterinary care, which is attributed to veterinary expertise barriers. The findings highlight a gap in the provision of veterinary services for fish, underscoring the need for enhanced education and training for veterinary professionals in aquatic medicine. As fish are often valued less as individuals and more in terms of the aquarium environment, the study recommends that improving fish welfare requires providing access to information that reflects value-based disparities between mammalian and aquatic pets.

Social learning and cultural enrichment for fish welfare

Social learning and cultural enrichment for fish welfare

A case study on the effect of aquaculture operations on the physiology and behaviour of Atlantic salmon (Salmo salar) during two heat events on a commercial farm

Aquaculture farms represent a complex 3D environment and face regular seasonal challenges such as acute and chronically elevated temperatures during summer. Further, fish are exposed to the interaction between their environment and farm operations, which can cause challenging conditions. In the context of modern net-pen aquaculture and ocean warming, there is therefore a need to understand the welfare of these commercially important species under the realistic conditions they encounter. Fish were tagged with two types of biologgers measuring temperature, heart rate, external acceleration, and depth of fish as they experienced standard aquaculture operations over two periods of thermal stress, one short-term and one long-term. The fish response during the thermal stress events was compared with the periods preceding and following both events, and an additional analysis was carried out to further explore the effects of feeding and farm operations. Fish displayed signs of both secondary and potentially tertiary stress in response to the short- and long-term heat event and both heart rate and acceleration increased in response to feeding but displayed a more nuanced response to operations. As part of the broader concept of precision fish farming, this research, based on data from 7 individual fish, represents a case study that presents the potential use of biologgers as tools for recognising early signs of stress by observing the secondary stress response, thereby demonstrating the potential for informed and timely stress identification to guide farm management decisions to enhance fish welfare and production efficiency in commercial aquaculture.

An adaptable, user-friendly score sheet to monitor welfare in experimental fish.

Fish are increasingly used as experimental animals across research fields. Currently, around a quarter of all experimental animals used are fish. Less than 20% of these are standard model species. Welfare assessments for experimental fish are in their infancy compared with those for rodents. This can be attributed to the diversity of species used, the relative recency of fish as the go-to model for research, and challenges to assess welfare in non-vocal underwater species. The lack of guidelines and tools presents a challenge for researchers (particularly, for newcomers), for ethics committees and for implementing refinement measures. Here, we present an adaptable, user-friendly score sheet for fish based on MS Excel. The parameters are based on a literature review, have been validated by expert interviews and evaluated by a fish pathologist. The tool allows scoring of individual fish as well as groups, calculates summary scores and visualizes trends. We provide the underlying literature, give use examples and provide instructions on the adaptation and use of the score sheet. We hope that this tool will empower researchers to include welfare assessment in their routines, foster discussions on fish welfare parameters among scientists, facilitate interactions with ethics committees and, most importantly, enable the refinement of fish experiments.

Antioxidant, metabolic and digestive biomarker responses of farmed Sparus aurata supplemented with Laminaria digitata

The present study aimed to investigate the effectiveness of supplemented diets with the brown macroalga Laminaria digitata in improving the antioxidant, metabolic and digestive performance in gilthead seabream (Sparus aurata), using a multi-biomarker approach. Three experimental diets supplemented with 1.5 %, 3 % and 6 % of dried powdered L. digitata were tested against a control diet. After 30 and 60 days, S. aurata juveniles were sampled and muscle, gut and liver tissues were collected. Results showed that fish fed with 1.5 % L. digitata exhibited higher specific growth rate (SGR) after 30 days. Additionally, at this supplementation level, there was a significant reduction in antioxidant enzyme activities (catalase, CAT; glutathione S-transferase, GST; superoxide dismutase, SOD) and in lipid peroxidation (LPO) in muscle and liver tissues. In contrast, gut antioxidant enzyme activity increased with higher macroalga concentrations (3 % and 6 %). Fish fed with 6 % L. digitata revealed a significant decrease in muscle aerobic potential (citrate synthase (CS) activity) but increased anaerobic capacity (lactate dehydrogenase (LDH) activity). Moreover, the 1.5 % L. digitata supplemented diets led to a significant increase in amylase activity after 30 days. After 60 days, fed with 6 % L. digitata showed lower hepatosomatic index (HSI) compared to animals fed on control diet. Additionally, trypsin activity was higher in fish fed the supplemented diets, especially at 3 % L. digitata. Pepsin activity was significantly supressed in fish fed diets with higher macroalga concentrations (3 % and 6 %). Overall, the current findings highlight the beneficial effects with lower doses of L. digitata on farmed marine fish performance and welfare. However, additional research is needed to establish the most cost-effective seaweed supplementation dose and validate this strategy at an industrial scale.

Enhancing farmed fish welfare: Evaluating the effectiveness of plant-based stress mitigating agents as sedatives in sea bass (Dicentrarchus labrax) following intraperitoneal vaccination

The effectiveness of vaccines may be compromised by the stress response induced by intraperitoneal/intramuscular (IP/IM) vaccination due to an intimate interaction between the neuroendocrine and immune systems. Essential oils (EOs), known for their antibacterial, antioxidant, and sedative properties, are potential candidates to mitigate this stress response. This study investigates the short-term sedative effect of two essential oil-based products, FishEase-C (FEC) and FishEase-L (FEL) in sea bass prior to intraperitoneal vaccination (IP). Physiological stress indicators (plasma cortisol, glucose, lactate) increased 1-h post-vaccination (hpv) as expected. Cortisol remained elevated up to 24 hpv in the N.P. vaccine and FEC + vaccine groups but decreased with FEL treatment (FEL + vaccine group). However, FEC at the tested concentration appeared to induce stress. The transcription of stress (gr, hsp70, cox2), immune (il1β, il6, tnfα), and antioxidant (gpx, sod, catalase) genes confirmed the vaccination-induced stress response, with mc2r transcription indicating increased cortisol production in vaccinated groups (N.P. vaccine and FEC + vaccine). FEL reduced stress at both physiological (e.g., cortisol) and transcriptional levels (e.g., hsp70, cox2 and il6) at either 1 or 24 hpv. It is worth noting that, from an inflammatory perspective, there was a big difference between tissues in terms of magnitude and pattern (treatment and time effects). The brain was more resistant to inflammation, while the head kidney and spleen showed heightened il1β expression (860-2100-fold). These findings support the use of FEL as a sedative before IP/IM vaccination in sea bass.

Advances in Vaccine Adjuvants for Teleost Fish: Implications for Aquatic Welfare and the Potential of Nanoparticle-Based Formulations.

Vaccine adjuvants are crucial for reinforcing the immunogenicity of vaccines. Therefore, they are widely used in the aquaculture sector as vaccine components, facilitating the efficient prevention of infectious diseases and promoting sustainable teleost fish growth. Despite their benefits, there has been a growing concern about the potential adverse effects of vaccine adjuvants in teleost fish, connoting a valid impact on their overall health and welfare. Among the adjuvants used in aquaculture vaccinology, nanoparticle-based formulations have given rise to a promising new alternative to traditional options, such as oil-based emulsions and aluminum compounds, offering the benefit of minimizing relevant side effects. The aim of this paper was to review the current status of the adjuvants used in aquaculture, provide a description and an evaluation of their mode of action and side effects, and explore the potential use of nanoparticle formulations as adjuvants to improve the efficacy of aquaculture vaccines. By demonstrating and assessing the equilibrium between teleost fish welfare and immunological efficacy, this review presents a collective perspective that will assist in establishing a framework for the utilization of effective species-specific practices around adjuvant use in aquaculture, while also addressing the challenges of welfare-friendly immunization.

Ice angling for northern pike (Esox lucius) with tip ups: Hook style affects angler catch and fish welfare

Catch and release ice angling exposes fish to environments and techniques that differ markedly from those in the open-water season. Accordingly, we studied the influence of quick-strike treble hooks and 0º offset circle hooks on aspects of northern pike (Esox lucius) capture and behaviour using tip-ups during the winter. Based on 221 northern pike captured over three winters, quick strike rigs with multiple hooks had higher catch success, but extended dehooking time and caused more foul hooking. Deep hooking events were infrequent but were most likely to occur when pike were captured on the single treble quick strike rig and circle hook. Camera footage revealed that pike were tentative and appeared to require considerable time to strike. Hook style had no influence on fish behaviour when striking. Our findings suggest that the use of triple treble quick strike rigs may provide benefits to anglers because they hook more and slightly larger fish and do not result in deep-hooking events. Circle hooks caught in the jaw most frequently and were the easiest to remove most of the time; however, they periodically deep-hooked fish, which was unexpected. Ultimately, angler tackle choice will affect their enjoyment of ice angling, and the potential for stress and injury to fish when using tip ups.

Integration of Automated Anomaly Detection with Real-Time Fish Stress Monitoring Using QR Code-Enabled Biosensors in Diverse Aquatic Environments

Background and Objectives:In our laboratory, we have developed a biosensor capable of monitoring fish blood glucose levels as an indicator of stress response in real time. Previous studies faced challenges with traditional communication systems using radio waves or visible light, which were susceptible to interference from water mediums and ambient light. Therefore, this research aimed to develop a stress response monitoring system that could transmit information even in seawater and freshwater environments, utilizing QR code technology with error correction capabilities and automatically detecting abrupt anomaly changes in sensor response values.Materials and Methods:The glucose biosensor was constructed using a needle-type electrode with a Pt/Ir wire (φ: 0.178 mm) as the working electrode and Ag/AgCl as the reference electrode, with glucose oxidase immobilized on the working electrode surface for glucose oxidation. A microcontroller development kit (M5Stack Core2) was employed to convert sensor response values into QR codes, allowing for voltage application to the sensor and QR code display based on sensor response values. An iOS application was developed as a reading module to enable communication via QR codes. Stress response was monitored using freshwater fish (Nile tilapia, Oreochromis niloticus) and saltwater fish (Largescale Blackfish, Girella punctata). Additionally, a model capable of detecting abnormal sensor data using a One-Class Support Vector Machine was created utilizing baseline glucose concentration data. This model was integrated into a webcam control program to attempt real-time and automatically detect abnormal data.Results and Discussion:The QR code display system using M5Stack Core2 proved effective in applying voltage to the glucose biosensor, converting sensor response values to QR codes, and displaying them on the LCD screen. Stress response monitoring of freshwater and saltwater fish resulted in data retrieval rates of 100% and 84.6%, respectively, demonstrating the feasibility of wireless monitoring via QR codes regardless of water type. Furthermore, the stress response monitoring system incorporating abnormal data detection capabilities successfully identified communication issues and variations in response values due to stress induction, providing user feedback. These results highlight the capability of the system to monitor fluctuations in fish blood glucose levels in real time, potentially contributing to addressing issues such as the spread of fish diseases and mortality caused by stress. Future efforts will incorporate cloud storage and remote access features to enable real-time data monitoring and analysis from any location.Conclusion:Developing a real-time wireless monitoring system using QR code technology significantly advances understanding and addressing fish stress responses. By enabling continuous monitoring of glucose levels in fish, the system has the potential to mitigate the adverse effects of stress-related diseases and mortality. Further enhancements, including cloud integration and remote access, aim to enhance the system's usability and accessibility for researchers and aquaculture professionals, ultimately contributing to improved fish welfare and management practices. Figure 1

High plant protein diet impairs growth performance and intestinal integrity in greater amberjack (Seriola dumerili): Molecular and physiological insights

The Mediterranean aquaculture industry that produces mainly seabream and seabass is exploring alternative plant-based protein sources for fish feeds together with the diversification of fish species. Effective plant-based formulations require diverse sources and additives to maintain fish welfare and growth, which is especially important for carnivorous species. In this scenario, the objective of the present study was to evaluate the impact of a high percentage of fishmeal replacement with protein of plant origin in Seriola dumerili, a fast-growing species with a high protein requirement. Two diets were developed: MAP (marine animal protein) with a protein content of 92 % of animal origin and PPB (plant protein blend) with a 50 % replacement of protein of animal origin with plant protein. We combined electrophysiology measurements with expression analysis of claudins and members of the SLC superfamily of solute carriers to unravel and characterise putative markers of intestinal integrity and absorption. The replacement resulted in shorter and lighter fish with a reduction in growth rate (SGR) from 2.6 to 2. We simultaneously observed lower transepithelial tissue resistance (TER), lower permeability, and decreased cld12 expression in the anterior intestine. In addition, we demonstrated a strong region-dependent electrogenic transport of essential amino acids, with the mid-intestine having the highest transport capacity. The comparative study performed in the mid-intestine with fish fed the MAP or the PPB diets exposed a negative effect of dietary replacement with plant protein. No significant dietary impact on di- and tri-peptide transporters (SLC15) was found at the molecular level. However, a clear region-dependent expression pattern of slc15a1, slc15a2, and slc15a4 was observed, which warrants further investigation. The expression pattern of slc7a5 showed the effect of the diet, but in contrast, the diet and intestinal region affected the expression of its functionally associated slc3a1 and slc3a2 for amino acid antiport, with the strongest effects in the posterior intestine. The integrity and absorption impairments detected in response to protein source replacement will likely underlie the significant growth differences observed between the two dietary regimes.

Optimism about Wild Fish Welfare

Optimism about Wild Fish Welfare

Jump nets passively isolate lice-infected salmon and enable targeted treatment using cleaner fish

Ectoparasitic salmon lice (Lepeophtheirus salmonis) are one of salmon aquaculture's greatest economic and environmental problems, which farmers expend considerable resources to control. Cleaner fish are a widely used method of continuous control and are deployed within farms to eat lice off salmon. There are concerns regarding the efficacy and welfare of cleaner fish in commercial farms, with a clear need for improvements. One way to improve efficacy is to increase encounter rates between salmon and cleaner fish by increasing their spatial overlap within cages. Here, we used ‘jump nets’—floating net pens deployed within sea-cages to passively collect jumping salmon—to selectively capture and treat lice-infected salmon using cleaner fish. We tested: i) if jump nets selected salmon with higher lice loads than the overall cage population, ii) if salmon jumped into nets with cleaner fish more frequently than those without cleaner fish, and iii) if lice levels were reduced in jump nets stocked with cleaner fish compared to jump nets with no cleaner fish. Jump nets caught salmon with 1.2 times higher lice loads than fish populations in cages. Remarkably, salmon jumped 1.6 times more frequently into nets with cleaner fish than those without – a result consistent across both species of cleaner fish tested and at 5 out of 6 sampling times. The prevalence of adult stages of salmon lice on salmon was reduced by both lumpfish (25 % lower) and ballan wrasse (14 % lower) over a 3-day period. Our results reveal that passive capture can be used for selective lice treatment using cleaner fish or other lice treatment methods.

A Global Synthesis of Environmental Enrichment Effect on Fish Stress

ABSTRACTThe 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.

Growing pains in upscaling: A constructive technology assessment of sea lice treatment innovations in the stagnating Norwegian aquaculture regime

Innovations that scale up, often have unintended, adverse effects. Dealing with adverse effects is especially challenging in bioeconomy transitions, in which the large-scale deployment of innovations may generate severe environmental damages. This study looks at the case of Norwegian aquaculture which has been embraced as a model to revitalize rural livelihoods and foster regional development in coastal areas, but currently faces stagnation. The main cause for the industry’s stagnating development is a parasitic sea lice, which treatments have adverse effects on ecology and fish welfare. We perform a Constructive Technology Assessment (CTA) involving diverse stakeholders in a Multi-Criteria Mapping (MCM) exercise on the viability, opportunities, and risks of different treatment options to cope with sea lice in Norwegian aquaculture. We find that this method is well-suited to identify diverse anticipatory views on possible solutions to the sea lice problem, allowing decision-makers to identify more democratic, holistic, and sustainable pathways to upscale the bioeconomy.

Unveiling Emerging Opportunistic Fish Pathogens in Aquaculture: A Comprehensive Seasonal Study of Microbial Composition in Mediterranean Fish Hatcheries.

The importance of microbial communities in fish hatcheries for fish health and welfare has been recognized, with several studies mapping these communities during healthy rearing conditions and disease outbreaks. In this study, we analyzed the bacteriome of the live feeds, such as microalgae, rotifers, and Artemia, used in fish hatcheries that produce Mediterranean species. Our goal was to provide baseline information about their structure, emphasizing in environmental putative fish pathogenic bacteria. We conducted 16S rRNA amplicon Novaseq sequencing for our analysis, and we inferred 46,745 taxonomically annotated ASVs. Results showed that incoming environmental water plays a significant role in the presence of important taxa that constitute presumptive pathogens. Bio-statistical analyses revealed a relatively stable bacteriome among seasonal samplings for every hatchery but a diverse bacteriome between sampling stations and a distinct core bacteriome for each hatchery. Analysis of putative opportunistic fish pathogenic genera revealed some co-occurrence correlation events and a high average relative abundance of Vibrio, Tenacibaculum, and Photobacterium genera in live feeds, reaching a grand mean average of up to 7.3% for the hatchery of the Hellenic Center of Marine Research (HCMR), 12% for Hatchery A, and 11.5% for Hatchery B. Mapping the bacteriome in live feeds is pivotal for understanding the marine environment and distinct aquaculture practices and can guide improvements in hatchery management, enhancing fish health and sustainability in the Mediterranean region.

A review of deep learning-based stereo vision techniques for phenotype feature and behavioral analysis of fish in aquaculture

The industrialization, high-density, and greener aquaculture requires a more precise and intelligent aquaculture management. Phenotypic and behavioral information of fish, which can reflect fish growth and welfare status, play a crucial role in aquaculture management. Stereo vision technology, which simulates parallax perception of the human eye, can obtain the three-dimensional phenotypic characteristics and movement trajectories of fish through different types of sensors. It can overcome the limitations in dealing with fish deformation, frequent occlusions and understanding three-dimension scenes compared to the traditional two-dimensional computer vision techniques. With the deep learning development and application in aquaculture, stereo vision has become a super computer vision technology that can provide more precise and interpretable information for intelligent aquaculture management, such as size estimation, counting and behavioral analysis of fish. Hence, it is very beneficial for researchers, managers, and entrepreneurs to possess a thorough comprehension about the fast-developing stereo vision technology for modern aquaculture. This study provides a critical review of relevant topics, including the four-layer application structure of stereo vision technology in aquaculture, various deep learning-based technologies used, and specific application scenarios. The review contributes to research development by identifying the current challenges and provide valuable suggestions for future research directions. This review can serve as a useful resource for developing future studies and applications of stereo vision technology in smart aquaculture, focusing on phenotype feature extraction and behavioral analysis of fish.

Water Quality Impact on Fish Behavior: A Review From an Aquaculture Perspective

ABSTRACTChanges in water quality significantly shape fish behavior, a crucial index reflecting the growth and welfare status of fish. Given the centrality of this relationship to aquaculture practices, a comprehensive understanding of how water quality dynamics influence fish behavior is imperative. While there have been some summaries of the effects of water quality parameters on fish physiology and growth, few reviews on their effects on fish behavior have been reported yet. This article reviews several water quality parameters which are of great concern in aquaculture from multiple facets of actual production, including physical parameters (water temperature and turbidity), chemical parameters (dissolved oxygen, salinity, pH, and inorganic nitrogen), and chemical pollutants (microplastics and crude oil), which have gained increasing attention from the researchers and aquaculture practitioners over the past decades. Variations in these water quality parameters can exert profound effects on fish physiology, metabolism, internal tissues and organs, and sensory perception, which influences fish behaviors such as swimming, schooling, feeding, predation, anti‐predation, aggression, courtship, as well as adaptive and stress‐related behaviors such as exploration, avoidance response, and anxiety‐like behavior. By synthesizing the behavioral changes caused by specific water quality parameters, this review aims to provide strong support for further water quality‐related research, thereby fostering environments conducive to both fish welfare and aquaculture productivity.

Determining the appropriate concentration of an anesthetic mixture in three different fish species with the PROMETHEE decision model.

Anesthesia is applied to protect fish welfare for reducing employee workload in aquaculture. The efficacy of the anesthetic agent varies depending on the fish species. In this study, the effect of a commercial anesthetic (VetiVital AquaSED) manufactured mainly with herbal extracts (includes eugenol, linalool, linalyl acetat etc.) on three different fish species (rainbow trout, common carp, and Danube sturgeon) was investigated. In addition, the best available concentration of the anesthetic mixture for each species was determined using the PROMETHEE decision model. Danube sturgeon showed more resistance to anesthetics than the other two species. It was determined that the increase in concentration caused histological deterioration in fish. On the other hand, hematological parameters were affected by the anesthetic mixture, and this effect returned to normal levels after 8 h. According to the multi-criteria decision model, the best available concentrations determined by considering 10 different criteria are 400, 480, and 675 mg L-1 for rainbow trout, common carp and Danube sturgeon, respectively. Future studies should focus on developing the most appropriate anesthesia mixture in terms of physiological and anesthesia effectiveness for the target fish species.

Understanding the welfare of aquarium fish

Understanding the welfare of aquarium fish