Zebrafish are obligate social animals whose welfare deteriorates significantly in isolation or inadequate group sizes. Evidence-based group housing standards are a critical welfare refinement for this widely used research species.
Zebrafish are profoundly social animals, and single housing or inadequate group sizes cause measurable welfare harm. Their natural behavior — tight shoaling, coordinated movement, social facilitation of feeding — depends on appropriate group sizes and social compositions. Research facilities often house zebrafish in small groups or isolated pairs for experimental convenience, without recognizing the welfare cost. Refinement standards requiring minimum group sizes, social visual contact between tanks, and environmental enrichment are achievable within the constraints of most research facilities and produce measurable welfare improvements without compromising experimental validity.