SHADING OF BREEDING HAPAS ENHANCES REPRODUCTIVE PERFORMANCE OF NILE TILAPIA (OREOCHROMIS NILOTICUS) AND SEED OUTPUT

摘要

During summer, temperature of water in fishponds often rises excessively high which has been aggravated further by global warming. When the water temperature reaches above 35°C it hampers growth and reproduction. Facing this critical problem, an experiment was conducted for 120 days during May - September 2015 to investigate the effects of shading on seed output of Nile tilapia (Oreochromis niloticus). The trial was conducted using 12 hapas (12m x 5m) with net cover installed in a green water pond randomly assigned four replications for each of the three treatments, namely; (i) black net; (ii) blue net; and (iii) without cover as "Control". Each hapa was initially stocked with 150 females (Mean weight ± SE, 118.8 ± 5.7 g) and 75 male Nile tilapia(Mean weight ± SE, 120.3 ± 4.6 g). During the trial period, pond water temperature ranged from 26.7°C - 37.8°C. Average weekly egg production was 15,622±842 hapa1 from the hapas shaded with black net, which was 9 % and 18 % higher than that from the control and the hapa shaded with blue net respectively. Percentage of clutch hapa 1 week-1 from the black shaded hapas increased by 9% and 10%, as compared to the one shaded with blue net and control hapa respectively. Present study, therefore, showedthat shading with black net helps increase seed output whereas blue net does not.