Abstract
Simple SummaryThe 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.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.
Highlights
The zebrafish Danio rerio has rapidly become one of the world’s most common laboratory animal species, and is used in a wide variety of research areas [1,2,3]
The basic diet provided to captive animals should meet all nutritional needs for health, interventions should provide some further welfare benefit to be considered ‘enriching’— this paper seeks to review the impacts of environmental enrichment, so possible nutritional benefits are not considered here
Another area which has not been explored in zebrafish is the potential welfare benefits of demand feeders—in aquaculture, demand feeders can contribute to reduced aggression and injury compared with fixed feeding regimens, and may allow fish to self-select diets based on individual nutritional requirements [113,114]
Summary
The zebrafish Danio rerio has rapidly become one of the world’s most common laboratory animal species, and is used in a wide variety of research areas [1,2,3]. Laboratory zebrafish usually receive little or no enrichment, with some people highlighting their concerns that enrichment may negatively affect standardisation, could increase staff burden, may be costly, or is not well supported by the available evidence [3,20,21] Such concerns over the effects of enrichment in laboratory settings are not new—for example, similar reservations were expressed in the past over the inclusion of enrichment for laboratory rodents. This review will explore the evidence for the effects of enrichment on zebrafish welfare, and will discuss the challenges, real and perceived, to providing more enrichment for laboratory zebrafish It seeks to stimulate further discussion and research into zebrafish enrichment, whilst emphasising the importance of properly validated environmental modifications. It emphasises that rather than asking whether zebrafish need enrichment at all, we should be considering what kind of enrichment zebrafish need and how best it can be provided
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