Salinity tolerance in superior genotypes of tilapia, Oreochromis niloticus, Oreochromis mossambicus and their hybrids

Attempts to produce reciprocal hybrids failed due to very low spawning frequency in O. niloticus × O. mossambicus crosses, thus all hybrids were only of O. mossambicus maternal origin. Results for the trials were consistent across replicates and a number of interesting trends were apparent. Overall, growth was higher for all genotypes at elevated salinities with O. niloticus relatively faster growing at low salinity and O. mossambicus at the higher salinities. The hybrids revealed high average positive heterosis for weight gain (1.24) and biomass gain (1.33) but less for FCR (1.08). Regression analyses of relative weight and biomass gain showed highly significant correlations with salinity. The hybrid was superior to O. mossambicus at all salinities and to O. niloticus at salinities above 10 ppt. Survival of O. niloticus was lower than the other genotypes at 22.5 and 30 ppt due to susceptibility to disease and possibly also stress. The implications for the development of tilapia for brackish water aquaculture are discussed.