Growth, salinity tolerance and microsatellite analysis of the F2 reciprocal hybrids of Oreochromis niloticus x Sarotherodon galilaeus at different salinities

Oreochromis niloticus (O), the sixth generation of Genetic Improvement of Farmed Tilapia, shows rapid growth but poor salt tolerance, while Sarotherodon galilaeus (S) exhibits opposite traits. To combine the traits, F-1 progeny was obtained through artificial fertilization. Fertile F-1 produced F-2 by natural spawning. The mean survival times, the median survival time (ST50) or the survival rate of hybrids was greater than O. niloticus in a gradual or an acute salinity change. Plasma osmolarity, [Na+] and [Cl-] of the hybrids fluctuated in 32 g L-1 water during a 24-h period, but eventually reached levels similar to fish in freshwater. O. niloticus female x S. galilaeus male (OS F-2) or S. galilaeus female x O. niloticus male (SO F-2) showed the fastest growth at 22.5 g L-1, equal to about 78.2% or 69.7% of O. niloticus at 0 and 3.87 or 3.45 times that of S. galilaeus at their individual optimum growth. Growth in OS F-2 was 12% faster than SO F-2. Microsatellite analysis showed that F-2 had more alleles, a higher polymorphism information content and greater observed and expected heterozygosity than O. or S. Population differentiation was not detected between F-1 and F-2. All the results indicated that F-2 could be exploited for commercial production under saline conditions.