Effect of Different Salinity and Ration Levels on Growth Performance and Nutritive Physiology of Milkfish, Chanos chanos (Forsskal) – Field and Laboratory Studies

To investigate the effect of inland groundwater salinity, and two ration levels on growth performance and nutrition physiology in milkfish, Chanos chanos, two experiments (Experiment 1 and 2) were conducted. In the first experiment (Expt. 1), a 100-day monoculture of Chanos chanos at two different salinities (10 and 25‰) was carried out in ponds andthe fish were fed on two different (4% and 6% BW d-1) ration levels. Irrespective of the salinity treatment, low ration favored high growth in fish grown at 25 ppt salinity. Carcass composition revealed high accumulation of protein, fat, energy and phosphorus in fish fed at low ration level and maintained at 25 ppt salinity. Irrespective of the salinity treatment, DO, BOD, pH and nutrients remained significantly (P<0.05) higher in ponds where the fish were fed at low ration level.Multivariate analysis revealed a significant positive correlation of nutrients and productivity indicating parameters with fish weight gain. The second experiment (Expt. 2) was conducted under laboratory conditions and the milkfish fry were exposed to five different salinity levels (10.0, 15.0, 20.0, 25.0 and 30.0 ‰) for 100 days. A control in fresh water (0.0 ppt) was also maintained. Irrespective of the salinity treatment, significantly (P<0.05) high growth, feed conversion efficiency and intestinal enzyme activity were observed in fish maintained at low (4%) ration level. Carcass composition, muscle and liver glycogen levels, muscle protein, viscero-somatic index (VSI) and hepato-somatic index (HSI) values were also significantly (P<0.05) affected not only by the salinity treatment but also by the ration level. Studies indicated that low ration level and high salinity favored high growth in milkfish.