Growth response of Nile Tilapia (Oreochromis niloticus) stocked at different densities in the LAKE-Kalassane basin in northwestern Senegal

Abstract

Nile Tilapia (Oreochromis niloticus) were reared at three different densities in concrete circular tanks to evaluate the effects of stocking density on growth, survival rate and food conversion ratio. Fish (mean weight, 12.13 ± 9.3 g; N: 970) were stocked in three densities as: low (T1 = 0.9 kg/m³ ), medium (T2 =  1.17 kg/m³ ) and high (T3 = 1.37 kg/m³ ) with three replicates. The growth trial lasted for 150 days. Bulk and individual weights of fish in each tank were  recorded monthly. The final mean weights of the fish stocked at densities of T1, T2 and T3 reached 79.66 ± 4.06; 55.80 ± 3.12 and 44.81 ± 6.21 g  respectively. The average survival rates at the end of the experiment were 92.9 ±1.1%; 80.88 ±1.92% and 97 ± 0.02% for treatments T1, T2 and T3  respectively. Calculated food conversion rates ranged from 0.98 in low density fish (T1), 0.85 in medium density fish (T2), and 0.83 in high density fish (T3).  The condition factor is equal to 1.76 in low density stocked fish (T1), followed by 1.77 in the medium density fish (T2) and finally 1.82 in high density  fish (T3). The regression coefficients a and b and the results of the weight-length analysis are deduced from the graphical representation of the weight- length relationship. The growth of O. niloticus is of negative allometric type. Indeed, the regression coefficients (b-values) of the weight-length  relationship of the individuals of the three treatments are lower than 3. This indicates that O. niloticus individuals reared in the different treatments tend  to grow more in height than in weight. The results revealed that the stocking densities in this study had no significant effect on growth and survival of O.  niloticus.