EFFECTS OF DIETARY CALCIUM AND VITAMIN-D3 ON WEIGHT-GAIN AND MINERAL-COMPOSITION OF THE BLUE TILAPIA (OREOCHROMIS-AUREUS) IN LOW-CALCIUM WATER
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Influences of dietary calcium and vitamin D3 (cholecalciferol) were evaluated with fingerling blue tilapia using a 22 factorial design. Four purified diets were formulated to contain 34% crude protein from egg albumin and casein with 3.20 kcal available energy/g. The basal diet (0.2 g Ca/kg) was supplemented with either 0 or 7.5 g Ca/kg (from CaCl22H2O) and 0 or 2000 IU vitamin D3/kg. Experimental diets were fed in triplicate to groups of blue tilapia initially averaging 2.300.09 g in 38-liter aquaria receiving water with <0.1 mg Ca/l for a period of 24 weeks. Significantly (P<0.05) greater weight gain and concentrations of ash, calcium, phosphorus and magnesium in bone and scale tissues were observed for fish fed the calcium-supplemented diets compared to those fed diets without supplemental calcium regardless of vitamin D3 supplementation. Fish fed the diet without supplemental vitamin D3 but with supplemental calcium had a significant reduction in weight gain at the end of 12 weeks compared to those fed the diet supplemented with both nutrients; this trend continued in subsequent weeks although differences were not significant. Effects of vitamin D3 on mineralization of hard tissues were negligible at all sampling periods. Dietary supplementation of vitamin D3 was not required for tilapia to utilize dietary calcium for growth and tissue mineralization. Based on these results, dietary calcium had the most profound effects on growth and mineral composition of blue tilapia reared in low-calcium water and effects of vitamin D3 were more subtle. 1994.
