IMPACTS OF FISH INTRODUCTIONS IN TROPICAL ASIA AND AMERICA

Biotas are constantly being reshaped by invasions. Introduction is now an added route to invaders. Impacts must be viewed against the background of massive changes in type, extent and quality of freshwater habits globally and in that freshwater fishes are almost living fossils. Also, old lakes and lacustrine fishes are highly restricted geographically. Lakes are young while rivers are old. Riverine, marsh and pond fishes are not well adapted to lacustrine conditions now widespread due to reservoir construction. Some Clupeidae and Cichlidae are lacustrine-adapted and highly productive. They have therefore made major impacts on fish yields in lakes and reservoirs. In tropical Asia and America, there have been a series of overlapping waves of fish introductions during the past 150 years; culminating tin the tilapias from Africa. These fishes now dominate capture and culture fisheries in many countries. Fish introductions are a fait accompli and will continue. They must be realistically assessed and carefully monitored. Contrary to some predictions, introductions have not caused severe damage to indigenous species except when piscivores were used. Yields of indigenous fishes have apparently been enhanced in some instances. Parasites pose a serious threat and only an effective quarantine will ensure their exclusion.