Effects of Dietary Calcium and Phosphorus on Growth Performance and Nutritive Physiology of Chanos Chanos (Forsskal) and Nile Tilapia, Oreochromis Niloticus (Linn.), Kept in Inland Saline Water

摘要

An experiment was carried out with Chanos chanos and Oreochromis niloticus fry to determine their dietary phosphorus and calcium requirements and their interactions, if any. Ten isoenergetic and isonitrogenous diets were formulated. To the basal diet were added different concentrations of phosphorus as di-hydrogen-orthophosphate (0.25, 0.375 and 0.5 100g~(-1) of diet) and calcium as calcium chloride (0.5, 0.75 and 1.0 g 100 g~(-1) of diet). These concentrations resulted in varying Ca-P ratios (2:1, 2:1.5, 1:1, 1.5:0.5, 1.5:1, 2:0.5 and 2:0.75). Calcium and phosphorus concentrations in the water at 10 ppt were 425 mg and 0.03 mg I~(-1) respectively. A diet without additional supplementation with Ca and P served as control. Irrespective of the fish species, significantly (P＜0.05) higher growth performance (growth per cent gain in body weight, SGR and final length), and higher values of APD, GPR, GER and PER were observed in fish which were fed on a diet containing calcium and phosphorus at a concentration of 0.5 g 100g~(-1) of diet (diet No. 4) in the ratio of 1:1. Lower FCR and low excretion of metabolites (N-NH_4 and o-PO_4) were also observed at these concentrations. Significantly (P＜0.05) high VSI, HIS, high accumulation of protein, higher digestive enzyme activity, lower muscle and liver glycogen levels and high muscle protein contents coincided with the highest growth performance observed in these studies. Diets containing higher (＜0.75 mg and above) or lower concentrations (＞0.5 mg) of calcium resulted in the deficiency signs such as reduced growth, high food conversion values, lower digestive enzyme activities and higher excretion of metabolites. These investigations thus have clearly revealed that a concentration of 0.5 g 100 g~(-1) of calcium and phosphorous in the diet appears to be optimum for obtaining high growth with lower food conversion ratio in milkfish and Nile tilapia.