Invasive aquatic species introduced through aquaculture and the pet trade compete with and predate native fish, causing ecological and welfare harm to wild populations.
Invasive species welfare concerns operate at the population and ecosystem level rather than primarily at the individual level. Native fish and invertebrates facing competition and predation from invasives suffer through reduced food access, predation injury, and population decline. White-clawed crayfish dying from crayfish plague suffer acute disease impacts at scale. Zander predation on prey fish species causes welfare harm to individual prey animals. Aquaculture biosecurity prevents the escape of farmed species that may become invasive. Never releasing aquarium fish into natural waterways is a direct welfare intervention. Invasive species control through trapping and removal is often necessary but involves welfare trade-offs for the trapped animals.