Wild freshwater fish face welfare challenges from water quality degradation, barriers to migration, invasive species competition, and climate-driven temperature increases.
Wild freshwater fish welfare is compromised across every major river system in developed and developing countries through some combination of pollution, barriers, flow reduction, invasive species, and warming. Individual fish experiencing acute oxygen depletion events — caused by farm slurry runoff or algal bloom die-offs — die by suffocation in events that cause hundreds of thousands of deaths simultaneously with accompanying physiological distress. Fish unable to migrate past barriers circulate below obstacles attempting to find passage, expending energy and remaining at higher predation risk. Temperature stress as rivers warm past thermal tolerance limits causes chronic physiological stress over the weeks of summer. River restoration that addresses these stressors simultaneously improves individual welfare and population recovery.