EFFECTS OF DIETARY CALCIUM AND VITAMIN-D3 ON WEIGHT-GAIN AND MINERAL-COMPOSITION OF THE BLUE TILAPIA (OREOCHROMIS-AUREUS) IN LOW-CALCIUM WATER

Influences of dietary calcium and vitamin D3 (cholecalciferol) were ev aluated with fingerling blue tilapia using a 2 x 2 factorial design. F our purified diets were formulated to contain 34% crude protein from e gg albumin and casein with 3.20 kcal available energy/g. The basal die t (0.2 g Ca/kg) was supplemented with either 0 or 7.5 g Ca/kg (from Ca Cl2.2H2O) and 0 or 2000 IU vitamin D3/kg. Experimental diets were fed in triplicate to groups of blue tilapia initially averaging 2.30 +/- 0 .09 g in 38-liter aquaria receiving water with < 0.1 mg Ca/1 for a per iod of 24 weeks. Significantly (P < 0.05) greater weight gain and conc entrations of ash, calcium, phosphorus and magnesium in bone and scale tissues were observed for fish fed the calcium-supplemented diets com pared to those fed diets without supplemental calcium regardless of vi tamin D3 supplementation. Fish fed the diet without supplemental vitam in D3 but with supplemental calcium had a significant reduction in wei ght gain at the end of 12 weeks compared to those fed the diet supplem ented with both nutrients; this trend continued is subsequent weeks al though differences were not significant. Effects of vitamin D3 on mine ralization of hard tissues were negligible at all sampling periods. Di etary supplementation of vitamin D3 was not required for tilapia to ut ilize dietary calcium for growth and tissue mineralization. Based on t hese results, dietary calcium had the most profound effects on growth and mineral composition of blue tilapia reared in low-calcium water an d effects of vitamin D3 were more subtle.