Effect of stocking density on the growth and survival of improved (F5 and F6) and unimproved native strains of Oreochromis shiranus (Trewavas) raised in hapas

Abstract

Growth performance and survival rate of improved strains (F5 and F6) and unimproved native strain of Oreochromis shiranus was assessed. Three stocking densities (5, 7 and 9 fish m-3) were used to randomly allocate fingerlings, of mean weight 6±0.6 g, into 27 hapas. Hapas, measuring 9 m3 were fixed in a pond of 700 m2. Stocking density significantly (p<0.05) affected the growth of the 3 strains though there was no significant difference between stocking density of 5 and 7 fish m-3. The highest final weight was noted at a stocking density of 5 fish m-3 with an average weight of F6 being 28.1 g, followed by F5 (24.9 g) and unimproved strain (24.0 g). F6 strain had a higher final mean weight (23.41 g) followed by F5 (21.84 g) and then unimproved strain (18.70 g), but there was no significant difference between the two improved strains (p>0.05). The apparent genetic gain due to selection ws estimated to be 16.8 and 25.2% between the unimproved strain and F5, F6 strains, respectively. Based on the results, farmers can be encouraged to use F6 strain at a stocking density of 5 fish m-3. The revelation that there was no difference between the improved strains has implications on the continuation of the selection program.