Zebrafish are among the most widely used vertebrates in biomedical research, with growing recognition that their welfare requirements have been significantly underestimated.
Zebrafish welfare has historically been undervalued because their small size and aquatic lifestyle made welfare assessment difficult. Research now confirms they are capable of experiencing pain, fear, and stress, with neurological and endocrine systems that respond to adverse stimuli in ways analogous to mammals. In research settings, zebrafish are frequently housed at densities that cause social stress, with inadequate environmental enrichment and inconsistent water quality management. Group housing provides significant welfare benefits - isolated zebrafish show elevated cortisol and impaired immune function. In aquaria and home settings, zebrafish are often kept in small tanks with insufficient companions, ignoring their schooling nature. As their welfare capacity becomes better understood, both research and hobby communities need to update housing standards to reflect the genuine welfare needs of these small but sentient fish.