Zebrafish are among the most widely used laboratory animals globally, and growing evidence for their sentience is driving improved welfare standards in husbandry, experimental design, and regulated procedures.
Zebrafish welfare in research is an area of rapidly evolving standards as the evidence for fish sentience becomes increasingly difficult to ignore. The historical assumption that fish are simple reflex organisms has been substantially challenged by research showing zebrafish demonstrate anxiety-like states, show place conditioning toward analgesic environments following noxious procedures, and show complex social behaviour that is disrupted by isolation. Laboratory housing standards that maintain zebrafish in sparse, barren tanks with minimal environmental complexity fail to meet their behavioural needs and likely impose chronic welfare costs through impoverished environments. Social housing that maintains group structure appropriate to shoaling species, substrate and cover enrichment, and structured flow conditions that allow swimming against mild current all contribute to positive welfare. The Three Rs framework — replacement, reduction, refinement — applied to zebrafish research requires genuine engagement with their welfare needs rather than treating them as lower-concern than mammals simply because of their phylogenetic position.