GROWTH AND REPRODUCTION OF INDIVIDUALLY TAGGED NILE TILAPIA (OREOCHROMIS-NILOTICUS) OF DIFFERENT STRAINS

Growth and reproduction traits were observed in seven strains of Oreoc hromis niloticus from Egypt, Ghana, and Senegal (bred from wild collec ted stocks recently imported to the Philippines from Africa), and 'Isr ael','Singapore', 'Taiwan' and 'Thailand' (strains maintained for aqua culture purposes in the Philippines), respectively. Twenty individuall y tagged fish were stocked separately for each strain in 1-m3 fine mes h hapas installed in outdoor concrete tanks and weighed every 2 weeks from 60 days to 210 days. There were no significant differences (P<0.0 5) in growth among strains with the exception of Ghana which showed a significantly lower body weight at 210 days (P<0.05). Based on ages at first spawning, three phenotypes of females were distinguished: early spawning, late spawning and females that did not reproduce during the experiment (virgin females). Growth performances of late spawning and virgin females were nearly equal to the male growth performance in so me of the strains tested. This indicates that if reproduction can be d elayed in the females, average growth rates comparable to those of an all-male population might be achieved. Phenotypic correlations observe d between age and female body weight at first spawning ranged from 0.7 7 to 0.99; age and number of eggs at first spawning, 0.30 to 0.81; and female body weight at first spawning with the number of eggs produced , 0.64 to 0.76. Overall, the correlations between these traits were si gnificant (P<0.05).