SALINITY TOLERANCE OF GENETICALLY PRODUCED TILAPIA (OREOCHROMIS) HYBRIDS

A genetic breeding program was carried out to create a hybrid tilapia (Oreochromis) with high salinity tolerance, fast growth and uniform re d skin color. The hybrids were obtained by crossing males from a line with high salinity tolerance (a cross between O. mossambicus and the N D9 line) with females from a fast-growing line of red tilapia (ND5). T he new hybrid is called ND60. The growth performance of the ND60 hybri d was tested in tanks with a water salinity of 41 ppt and compared wit h that of the ND21 hybrid, grown in fresh water. When stocked at 103 g , ND60 and ND21 demonstrated specific growth rates of 1.17% and 1.32%, respectively. When stocked at 248 g, they demonstrated specific growt h rates of 0.94% and 1.02%, respectively. ND60 stocked in high salinit y grew approximately 10% slower than ND21 in fresh water. Growth trial s in commercial cages were conducted in the Mediterranean Sea and in t he Red Sea, which differ in salinity and temperature regimes. In the M editerranean, ND60 of 70-265 g demonstrated a daily weight gain of 2.2 g per day, suitable for commercial production in sea water (37 ppt). However, growth slowed down significantly when the water temperature d ropped below 25 degrees C and stopped altogether at water temperatures lower than 21 degrees C. In the Red Sea, where the water temperature fluctuates between 21 degrees C and 25 degrees C, growth was fairly co nstant at 0.55 g per day, a slow growth rate which can be explained by the relatively low water temperature. Our results indicate that the n ew ND60 hybrid incorporates the tolerance to high salinity from its O. mossambicus ancestor with the fast growth and red skin color from its ND9 and ND5 parents. These hybrids conform to typical temperature res trictions and grow best at water temperatures higher than 25 degrees C .