Shade as enrichment: testing preferences for shelter in two model fish species

Habitat Enrichment Causes Changes in Fish Behavioural Characteristics: A Case Study of Sparus latus

To better understand the habitat preferences and behavioural ecology of Sparus latus, we performed an experiment using box-shaped reefs as habitat enrichment materials, allowing us to determine the behavioural strategies and drivers involved in the response to different enrichment structures. The results showed that the first contact time of S. latus was negatively correlated (Pearson's correlation, p < 0.005) with the distribution rate in the artificial reef area. Enrichment structures affected the habitat preferences of S. latus, and there was a significant difference in the average distribution rate between the control and treatment groups (Adonis, p < 0.001). The opening ratio (Adonis, R2 = 0.36) explained the distribution difference of S. latus better than the opening shape (Adonis, R2 = 0.12). In the absence of an enrichment structure, S. latus remained more active during the daytime, exhibiting poor clustering, while in the presence of an enrichment structure, S. latus exhibited clustered movement at night. The opening ratio was negatively correlated with the average interindividual distance (Spearman's correlation, p < 0.01) and showed a significant positive correlation with the average distribution rate in the reef area (Spearman's correlation, p < 0.001), indicating that the reef opening ratio significantly affected the reef-tropism and clustering behaviours of S. latus. The light intensity was negatively correlated with the average distance moved, and the average speed (Spearman's correlation, p < 0.05) was significantly positively correlated with the reef first contact time (Spearman's correlation, p < 0.001), indicating that the light intensity affected the exploration and activity patterns of S. latus. These results provide a research basis for analysing the pattern and process of fish proliferation induced by artificial reef habitats.

A systematic review of the impact of environmental enrichment in zebrafish

Environmental enrichment (EE) consists of a series of interventions carried out in the home environment to promote greater exposure to sensory stimuli and mimic the natural habitat of laboratory-housed animals, providing environments closer to those found in nature. Some studies have shown the positive effects of EE in zebrafish housed in a laboratory environment. However, this evidence is still recent and accompanied by contradictory results. Furthermore, there is great variability in the protocols applied and in the conditions of the tests, tanks and materials used to generate an enriched environment. This substantial variability can bring many uncertainties to the development of future studies and hinder the reproducibility and replicability of research. Here, in this context, we carried out a systematic review of the literature, aiming to provide an overview of the EE protocols used in zebrafish research. The literature search was performed in PubMed, Scopus and Web of Science and the studies were selected on the basis of predefined inclusion/exclusion criteria. A total of 901 articles were identified in the databases, and 27 of those studies were included in this review. We conducted data extraction and risk-of-bias analysis in the included studies. Among these studies, the effect of EE was evaluated in two different ways: (1) for animal welfare and (2) as an intervention to prevent behavioral, biochemical, molecular, developmental and breeding dysfunctions. Although the EE protocols in zebrafish presented a series of experimental differences, the results showed that the benefits of the EE for zebrafish were consistent. According to the results described here, the use of EE in the zebrafish home tank improves welfare and may reduce sources of bias in scientific research. However, it is still necessary to develop standardized protocols to improve the application of EE in scientific studies using zebrafish.

Maze design: size and number of choices impact fish performance in cognitive assays

Although studies on fish cognition are increasing, consideration of how methodological details influence the ability to detect and measure performance is lagging. Here, in two separate experiments the authors compared latency to leave the start position, latency to make a decision, levels of participation and success rates (whether fish entered the rewarded chamber as first choice) across different physical designs. Experiments compared fish performance across (a) two sizes of T-mazes, large and standard, and a plus-maze, and (b) open choice arenas with either two or four doors. Fish in T-mazes with longer arms took longer to leave the start chamber and were less likely to participate in a trial than fish in T-mazes with shorter arms. The number of options, or complexity, in a maze significantly impacted success but did not necessarily impact behavioural measures, and did not impact the number of fish that reached a chamber. Fish in the plus-maze had similar latencies to leave the start box and time to reach any chamber as fish in the same-sized T-maze but exhibited lower overall success. Similarly, in an open choice arena, increasing the number of options - doors to potential reward chambers - resulted in lower probability of success. There was an influence of reward position in the choice arena, with rewarded chambers closest to the sides of the arena resulting in lower latencies to enter and higher probability of decision success. Together the results allow the authors to offer practical suggestions towards optimal maze design for studies of fish cognition.

Fish Welfare in Public Aquariums and Zoological Collections

A wide variety of fish species have been displayed in public aquariums and zoological collections for over 150 years. Though the issue of pain perception in fish is still being debated, there is no disagreement that negative impacts on their welfare can significantly affect their health and wellbeing. A general description of the basic biological requirements for maintaining fish in captive environments is presented, but species-specific information and guidelines should be developed for the multitude of species being maintained. A combination of behavioral, performance, and physiological indicators can be used to assess the well-being of these animals. Ultimately, the goal for optimizing the welfare of fish should be to provide the best possible environment, husbandry, and social interactions to promote natural species-specific behaviors of the fish in captivity.

Housing Conditions Affect Adult Zebrafish (Danio rerio) Behavior but Not Their Physiological Status

Zebrafish is a valuable model for neuroscience research, but the housing conditions to which it is exposed daily may be impairing its welfare status. The use of environmental enrichment and the refinement of methodology for cortisol measurement could reduce stress, improving its welfare and its suitability as an animal model used in stress research. Thus, this study aimed to evaluate (I) the influence of different housing conditions on zebrafish physiology and behavior, and (II) skin mucus potential for cortisol measurement in adult zebrafish. For this, AB zebrafish were raised under barren or enriched (PVC pipes and gravel image) environmental conditions. After 6 months, their behavior was assessed by different behavioral paradigms (shoaling, white-black box test, and novel tank). The physiological response was also evaluated through cortisol levels (whole-body homogenates and skin mucus) and brain oxidative stress markers. The results revealed that enriched-housed fish had an increased nearest neighbors' distance and reduced activity. However, no effect on body length or stress biomarkers was observed; whole-body and skin mucus cortisol levels had the same profile between groups. In conclusion, this study highlights the skin mucus potential as a matrix for cortisol quantification, and how housing conditions could influence the data in future studies.

Effects of shady environments on fish collective behavior

Despite significant efforts devoted to understanding the underlying complexity and emergence of collective movement in animal groups, the role of different external settings on this type of movement remains largely unexplored. Here, by combining time series analysis and complex network tools, we present an extensive investigation of the effects of shady environments on the behavior of a fish species (Silver Carp Hypophthalmichthys molitrix) within earthen ponds. We find that shade encourages fish residence during daylight hours, but the degree of preference for shade varies substantially among trials and ponds. Silver Carp are much slower and exhibit lower persistence in their speeds when under shade than out of it during daytime and nighttime, with fish displaying the highest persistence degree and speeds at night. Furthermore, our research shows that shade affects fish schooling behavior by reducing their polarization, number of interactions among individuals, and the stability among local neighbors; however, fish keep a higher local degree of order when under shade compared to nighttime positions.

Improving zebrafish laboratory welfare and scientific research through understanding their natural history

Globally, millions of zebrafish (Danio rerio) are used for scientific laboratory experiments for which researchers have a duty of care, with legal obligations to consider their welfare. Considering the growing use of the zebrafish as a vertebrate model for addressing a diverse range of scientific questions, optimising their laboratory conditions is of major importance for both welfare and improving scientific research. However, most guidelines for the care and breeding of zebrafish for research are concerned primarily with maximising production and minimising costs and pay little attention to the effects on welfare of the environments in which the fish are maintained, or how those conditions affect their scientific research. Here we review the physical and social conditions in which laboratory zebrafish are kept, identifying and drawing attention to factors likely to affect their welfare and experimental science. We also identify a fundamental lack knowledge of how zebrafish interact with many biotic and abiotic features in their natural environment to support ways to optimise zebrafish health and well-being in the laboratory, and in turn the quality of scientific data produced. We advocate that the conditions under which zebrafish are maintained need to become a more integral part of research and that we understand more fully how they influence experimental outcome and in turn interpretations of the data generated.

Natural Habitat Design for Zoo-Housed Elasmobranch and Teleost Fish Species Improves Behavioural Repertoire and Space Use in a Visitor Facing Exhibit

Simple Summary

Studies investigating whether a captive environment is meeting the needs of the species housed are relatively common among captive mammals. However, studies exploring fish behaviour in captive display enclosures are far less common in the scientific literature. Focusing on a small group of sharks, rays and smaller fish within a single display, our objectives were to; assess whether the behaviours of a select number of individual fishes within a single display are altered after the environment is enriched to enhance environmental complexity and visitor exposure is reduced, and also to increase our understanding of captive fish behaviour to improve capacity for evidence-based management decisions. In summary, increased environmental complexity and reduced visitor interaction showed correlations with increased expression of natural behaviours in all fish studied, including increased space use and decreased abnormal repetitive behaviours in some species. These results reflect a change toward more natural wild behavioural time budgets. Studying behaviour change in fish in different environmental conditions provides a good basis for evidence-based decision making.

Abstract

This study investigated the behaviour of two Elasmobranch species; Southern fiddler ray (Trygonorrhina dumerilii, n = 1) and Port Jackson shark (Heterodontus portusjacksoni, n = 4) and two teleost species; moonlighter (Tilodon sexfasciatus, n = 1) and banded morwong (Cheilodactylus spectabilis, n = 1) living within a single enclosure. For this study, two treatments were compared, the original enclosure design, and then after the enclosure had been renovated to more closely represent the species natural habitats, with a raised front viewing glass to prevent visitor interaction. Behaviours such as resting, swimming and abnormal behaviours such as surface and perimeter swimming (elasmobranchs only) were recorded as well as location within the enclosure, for 10 days pre and 10 days post renovation. The Port Jackson sharks significantly reduced the performance of abnormal behaviours after renovation, and significantly increased the time spent near the exhibit front. The Southern fiddler ray increased resting post renovation, while the teleost species also spent more time near the exhibit front. Although a small sample size was used, the results suggest that a more naturalistic environment with multiple micro-habitats and effective visitor barriers allows for a greater proportion of the day spent exhibiting natural behaviours, greater space use and reduced stereotypes.

Different influences of anxiety models, environmental enrichment, standard conditions and intraspecies variation (sex, personality and strain) on stress and quality of life in adult and juvenile zebrafish: A systematic review

Antagonist and long-lasting environmental manipulations (EM) have successfully induced or reduced the stress responses and quality of life of zebrafish. For instance, environmental enrichment (EE) generally reduces anxiety-related behaviours and improves immunity, while unpredictable chronic stress (UCS) and aquarium-related stressors generate the opposite effects. However, there is an absence of consistency in outcomes for some EM, such as acute exposure to stressors, social enrichment and some items of structural enrichment. Therefore, considering intraspecies variation (sex, personality, and strain), increasing intervention complexity while improving standardisation of protocols and contemplating the possibility that EE may act as a mild stressor on a spectrum between too much (UCS) and too little (standard conditions) stress intensity or stimulation, would reduce the inconsistencies of these outcomes. It would also help explore the mechanism behind stress resilience and to standardise EM protocols. Thus, this review critically analyses and compares knowledge existing over the last decade concerning environmental manipulations for zebrafish and the influences that sex, strain, and personality may have on behavioural, physiological, and fitness-related responses.

Physical enrichment research for captive fish: Time to focus on the DETAILS

Growing research effort has shown that physical enrichment (PE) can improve fish welfare and research validity. However, the inclusion of PE does not always result in positive effects and conflicting findings have highlighted the many nuances involved. Effects are known to depend on species and life stage tested, but effects may also vary with differences in the specific items used as enrichment between and within studies. Reporting fine-scale characteristics of items used as enrichment in studies may help to reveal these factors. We conducted a survey of PE-focused studies published in the last 5 years to examine the current state of methodological reporting. The survey results suggest that some aspects of enrichment are not adequately detailed. For example, the amount and dimensions of objects used as enrichment were frequently omitted. Similarly, the ecological relevance, or other justification, for enrichment items was frequently not made explicit. Focusing on ecologically relevant aspects of PE and increasing the level of detail reported in studies may benefit future work and we propose a framework with the acronym DETAILS (Dimensions, Ecological rationale, Timing of enrichment, Amount, Inputs, Lighting and Social environment). We outline the potential importance of each of the elements of this framework with the hope it may aid in the level of reporting and standardization across studies, ultimately aiding the search for more beneficial types of PE and the development of our understanding and ability to improve the welfare of captive fish and promote more biologically relevant behaviour.

Enrichment for Laboratory Zebrafish-A Review of the Evidence and the Challenges

Simple Summary

The zebrafish is one of the most commonly used animals in scientific research, but there remains a lack of consensus over good practice for zebrafish housing and care. One such area which lacks agreement is whether laboratory zebrafish should be provided with environmental enrichment—additions or modifications to the basic laboratory environment which aim to improve welfare, such as plastic plants in tanks. The need for the provision of appropriate environmental enrichment has been recognised in other laboratory animal species, but some scientists and animal care staff are hesitant to provide enrichment for zebrafish, arguing that there is little or no evidence that enrichment can benefit zebrafish welfare. This review aims to summarise the current literature on the effects of enrichment on zebrafish physiology, behaviour and welfare, and identifies some forms of enrichment which are likely to benefit zebrafish. It also considers the possible challenges that might be associated with introducing more enrichment, and how these might be addressed.

Abstract

Good practice for the housing and care of laboratory zebrafish Danio rerio is an increasingly discussed topic, with focus on appropriate water quality parameters, stocking densities, feeding regimes, anaesthesia and analgesia practices, methods of humane killing, and more. One area of current attention is around the provision of environmental enrichment. Enrichment is accepted as an essential requirement for meeting the behavioural needs and improving the welfare of many laboratory animal species, but in general, provision for zebrafish is minimal. Some of those involved in the care and use of zebrafish suggest there is a ‘lack of evidence’ that enrichment has welfare benefits for this species, or cite a belief that zebrafish do not ‘need’ enrichment. Concerns are also sometimes raised around the practical challenges of providing enrichments, or that they may impact on the science being undertaken. However, there is a growing body of evidence suggesting that various forms of enrichment are preferred by zebrafish over a barren tank, and that enriched conditions can improve welfare by reducing stress and anxiety. This review explores the effects that enrichment can have on zebrafish behaviour, physiology and welfare, and considers the challenges to facilities of providing more enrichment for the zebrafish they house.