Facial action coding systems - long used in mammals - are being developed for fish to provide objective welfare assessment based on observable facial muscle movements associated with pain states.
The development of objective pain assessment tools for fish would represent a significant advance for aquatic animal welfare. Current assessment of fish welfare relies heavily on behavioral observation and physiological biomarkers that require sampling. Validated facial or behavioral action coding systems would allow non-invasive, real-time welfare assessment in aquaculture settings and research contexts. This matters practically because management interventions to improve welfare cannot be efficiently evaluated without standardized measurement tools. The scientific work required to develop and validate such tools requires recognition that fish welfare assessment is worth investing in - itself a consequence of accepting that fish pain and welfare matter morally. The development of fish welfare assessment tools is both a scientific challenge and a statement of values about which species deserve welfare consideration.