COMPENSATORY GROWTH FOR DIFFERENT STOCKING PRACTICES IN NILE TILAPIA (OREOCHROMIS NILOTICUS) FINGERLINGS

Mohamed M. Said

Aquaculture Department, Faculty of Fish Resources, Suez University, Suez, Egypt.

Received 1/ 3/ 2016

Accepted 28/ 4/ 2016

Abstract

The objective of this work was to verify the occurrence of compensatory growth in Nile tilapia (Oreochromis niloticus) reared in hapas, after being stocked at high densities, followed by a period under different lower densities. Nile tilapia monosex fingerlings (mean 1.4g ± standard error 0.02) were used to establish six experimental groups with varied stocking density schedules: two control groups A1 and B1 (15 and 30 fish / m2,
respectively); A2 and B2 (30 and 60 fish /m2 then reduced to 15 and 30 fish /m2 after 4 weeks, respectively); A3 and B3 (60 and 120 fish /m2 then reduced to 30 and 60 fish /m2 after 4 weeks and re-reduced to 15 and 30 fish /m2 after 8 weeks, respectively).The experiment lasted for 12 weeks, six experimental periods 2 weeks each. Decreasing stocking density in the experimental groups A2, A3, B2, and B3 after 4 weeks was accompanied with notable increase in the specific growth rate (SGR %) and decrease in feed conversion ratio (FCR) during the 3rd experimental period (4-6 weeks). Returned decrease the stocking density in A3 and B3
after 8 weeks results in another phase of compensatory growth response in terms of better growth rate and feed utilization. Final body weight of A1, A2, and A3 (19.39, 19.48, and 19.22 g, respectively) didn’t differ significantly while final body weight of B2 (16.41 g) was significantly
(p≤ 0.05) higher than those of B1 (14.22 g) and B3 (12.93 g). Overall SGR% didn’t differ significantly between A1, A2, and A3 (3.12, 3.13, and 3.11, respectively) whereas, B2 showed a significantly (p≤ 0.05) higher SGR% (2.93) than those of B1 and B3 (2.76 and 2.65, respectively). Feed conversion ratio was significantly (p≤ 0.05) lower in A3 (2.21) while the control group B1 showed the highest FCR (2.85). Body moister and ash contents tend to be higher while lipids and protein tends to be lower in the experimental groups which expressed compensatory growth response as compared with the control groups. The results of this study suggest full and over compensation response in Nile tilapia fingerlings
for reducing stocking density in different regulations which may be used in optimizing space and feed utilization in tilapia production.

Key words: Nile tilapia, stocking density, compensatory growth, body composition.