1. Introduction
Although a large number of fish species are being cultured, the
bulk of aquaculture and fisheries enhancement production is
accounted for by a small number of species which have been
introduced widely beyond their native ranges (Welcomme, 1988;
DIAS, 2004). Herbivorous or omnivorous tilapia and carp species are a
case in point, having been introduced throughout the tropics and
accounting for about 80% of tropical inland aquaculture production.
Like the common agricultural animal domesticates, these species have