Invasive freshwater fish including carp, trout, and tilapia outcompete native species, disrupt habitats, and reduce welfare for native aquatic communities.
Invasive freshwater fish cause welfare harm to native species through mechanisms that range from direct predation to competitive exclusion and habitat degradation. Native fish who lose nesting territories to aggressive invaders experience chronic stress from repeated displacement. Prey fish with no predator adaptation are caught and eaten without escape behavioral repertoire. The welfare scale of invasive freshwater fish impacts is enormous given the global extent of fish introduction events. Prevention — biosecurity at the border and between water bodies — is the most welfare-effective intervention.