Zebrafish have become a major research model organism, but welfare standards for this small fish species remain less developed than for mammals used in research.
Zebrafish are social schooling fish that show stress responses when isolated, including increased cortisol and altered behavior. Research housing frequently keeps small numbers of fish in tanks too small for normal schooling behavior. The gradient of regulatory protection — with embryos unprotected, larvae partially protected, and adults covered — creates welfare gaps at early life stages. Fish show behavioral and physiological responses to noxious stimuli consistent with pain, yet pain management during research procedures is rarely considered for fish of any size.