Response to selection for growth in an interspecific hybrid between [i]Oreochromis mossambicus[/i] and [i]O. niloticus[/i] in two distinct environments

The development of a saline tolerant tilapia strain able to grow fast is of importance in the Philippines, where 240,000 ha of brackish water ponds are available. To this end, founder hybridization between Oreochromis niloticus (with favorable growth traits) and Oreochromis mossambicus (with favorable salinity tolerance traits) was performed and followed by backcrossing with O. mossambicus to develop a strain highly tolerant to saline environments. Genetic selection for growth performance was subsequently conducted. The aim of the present study was to estimate growth performance and survival of the hybrid in two rearing environments following four generations of genetic selection. A comparison between the hybrid and an internal reference line was performed in two distinct environments: one intensive (tanks: feed and high stocking density) and one extensive (fertilized earthen ponds: without feed and low stocking density) system. The selection experiment consisted of a within group or within family selection with a random mating system. The selection criterion was body weight at five months, and salinity tolerance was passively selected by rearing fish in brackish water. After four generations of selection, the average body weight of the hybrid had increased by 50 g compared to the red tilapia internal reference line, which corresponds to a gain of 12.5 g or 7.3% per generation. Average weight in the intensive system was greater than in the extensive system (65.8 and 38.7% at the last generation in male and female, respectively). Realized heritability of body weight was only significant in the intensive system (0.19 +/- 0.07 vs. 0.17 +/- 0.06 in the extensive system). This selection scheme was performed in brackish water, allowing a passive selection on salinity tolerance, as shown by the improvement of the survival rate according to the generation in intensive and extensive systems.