Individual catchability in the mixed group of Tilapia species Oreochromis mossambicus, O-niloticus, and their hybrids

Mixed groups of two different species of tilapia Oreochromis mossambicus, O. niloticus, and their hybrids obtained from a river in Ibusuki city, Kagoshima pref. Japan were kept in two concrete tanks and evaluated for their vulnerability to angling. After capture-recapture angling tests, electrophoretic analysis was applied to all specimens to examine the effect of the degree of introgrssion of O. mossambicus and O. niloticus on the individual catchability. The most vulnerable group (three times hooked repeatedly) was composed mainly of O. niloticus and the least vulnerable one (three times unhooked repeatedly) was composed mainly of O. mossambicus. In the hybrids of these species, however, the most vulnerable specimens did not necessarily include more alleles orginally from O. niloticus than those from O. mossambicus, and there was no correlation between the degree of introgression and the catchability. This result implies that the individual catchability in hybrids is mostly determined by a posteriori rather than a priori.