Aquaculture Crsp 22nd Annual Technical Report

Nile tilapia Oreochromis niloticus is one of the primary tilapia species being cultured. Much of the stocks being cultured are based on a limited number of collections from the wild, which may differ in their reproductive and growth characteristics. An evaluation of reproductive and growth characteristics of the Egypt, Ivory Coast, Sagana, and Lake Victoria strains of O. niloticus was done at Auburn University. Brood fish were stocked into individual 2 m3 hapas suspended in 20 m2 concrete tanks. Hapas were checked weekly for successful spawners. Females found holding eggs or sac fry in their mouths were removed and transferred to the hatchery for weighing, counting, and subsequent incubation of eggs and sac fry in 40-L aquaria until hatching. Growth was evaluated at primary and secondary nursery stages. In the secondary nursery stage, growth was studied in outdoor concrete tanks and indoor aquaria on a recirculating system. There were no significant differences (P > 0.05) among the four strains in relative fecundity (eggs/g female weight). However, significant differences among strains in spawning and incubation successes were observed. There were no significant differences in growth performance among the strains (P > 0.05). However, significant growth differences were observed across production systems at the secondary nursery stage. The microsatellite variability of the above four strains of O. niloticus was described using thirteen primer pairs from O. niloticus in amplification reactions. Amplification products were subjected to electrophoresis on 7 % acrylamide gel followed by manual scoring of alleles. Results obtained showed moderate overall strain differentiation with an overall FST value of 0.18. All four strains showed some heterozygote deficiency when tested for Hardy-Weinberg equilibrium with observed heterozygosities falling short of expected values. Length of domestication impacted genetic diversity with Ivory Coast strain showing reduced genetic diversity observed in low number of both total and rare alleles.