Response of juvenile abalone, Haliotis discus hannai, to dietary calcium, phosphorus and calcium/phosphorus ratio

Abstract

The feeding experiment was conducted to determine the response of juvenile abalone, Haliotis discus hannai, to dietary calcium, phosphorus and the ratios of calcium to phosphorus. Fifteen isonitrogenous (approximately 30% CP) casein–gelatin-based diets containing five graded levels of phosphorus (0%, 0.5%, 1.0%, 1.5% and 2.0%) for each of three levels of calcium (0%, 1.0% and 2.0%) were fed to the animals previously fed a basal diet (0.23% total P and 0.17% total Ca) for 14 days. After 16 weeks of feeding, survival ranged from 94.7% to 100.0% with no significant difference among dietary treatments. The weight gain rate (WGR), daily increment in shell length (DISL), carcass concentrations of lipid and protein, soft-body alkaline phosphatase activity and phosphorus, zinc, manganese contents were significantly affected by dietary phosphorus levels. Supplementation of 1.0% and 2.0% calcium to the basal diet reduced soft-body phosphorus deposition and did not appear to increase the nutritive value of the diet, indicating that a dietary calcium supplement is not required under the present experimental conditions. The dietary phosphorus requirements were evaluated from the pooled WGR and DISL, respectively, by using the second-order polynomial regression analysis. On the basis of the pooled WGR and DISL, the optimum ranges of dietary available phosphorus were 0.65–1.17% (approximately 0.7–1.2% total P), and 0.64–1.14% (approximately 0.7–1.2% total P), respectively. Based on these results, about 1.15% available phosphorus (1.25% of total P) is recommended for the maximum growth of H. discus hannai, and if dietary available phosphorus is reduced from 1.15% to 0.65%, the growth of the abalone may be depressed with 5% likelihood. The calcium/phosphorus ratio of the diets is not important within the range assessed (approximately 0.1:1–9.0:1).