Small Fish Welfare in Aquatic Research

Millions of small fish species including zebrafish, medaka and sticklebacks are used in research with minimal welfare oversight compared to mammals, despite growing evidence of their capacity for suffering.

Key Facts

Zebrafish are the second most used vertebrate in research globally; guppies, medaka and sticklebacks are also widely used
Fish were excluded from US federal welfare regulations (the Animal Welfare Act) until pressure in the 2020s began to change some institutional policies
Research demonstrates that small fish including sticklebacks show cortisol responses, pain avoidance learning and social stress comparable to larger vertebrates
Acute netting and handling of small fish causes a cortisol spike equivalent in magnitude to that seen in mammals under painful procedures
Group housing dramatically reduces stress in schooling species including zebrafish and medaka — single housing is still common in research
Anaesthetic protocols using MS-222 (tricaine) are effective for small fish and are increasingly required in welfare-conscious institutions

Welfare Considerations

Small fish in research suffer the double disadvantage of uncertain sentience and minimal regulatory protection. While scientific evidence for fish pain and stress has grown substantially, small species used in developmental biology and genetics research remain outside welfare frameworks in many jurisdictions. The practical barriers to improving their welfare are low — group housing, appropriate water quality, anaesthesia for procedures and humane euthanasia are all achievable without compromising research validity. The primary barrier is cultural: the assumption that these animals do not matter enough to warrant welfare consideration. Shifting this assumption through education, regulatory inclusion and institutional policy change would benefit enormous numbers of animals at low cost.

What You Can Do

Advocate for small fish to be included in national laboratory animal welfare legislation
Support institutional animal care committees in applying welfare standards consistently to all vertebrate species
Encourage research institutions to require anaesthesia for all procedures in small fish species
Back funding for research into welfare indicators and enrichment needs for commonly used small fish species
Support the 3Rs in aquatic research through funding bodies and advocacy for replacement alternatives development