The effect of different combinations of dietary calcium and phosphorus on the growth of juvenile Haliotis laevigata

A basal diet containing 0.45% Ca and 0.51% P was supplemented with 3, 2, 1 and 0% CaCO3 both with and without 0.5% NaH2PO4. Diets were fed to replicate groups (n = 4) of ten juvenile greenlip abalone (Haliotis laevigata) in 10 1 flow through aquaria for 61 days after a 21 day acclimation period. Absolute and specific growth rates were calculated for both shell length (SL) and whole wet body weight (BW). Dietary Ca supplementation did not significantly affect growth (P > 0.05), however the specific growth rate (BW) of animals fed diets supplemented with P was 7.9% higher than that of animals fed diets without P supplement (P < 0.05). There were no significant Ca x P interactions for growth indices (P > 0.05). Shell thickness was apparently unaffected by dietary Ca level. Mortality due to natural causes was not affected by diet (P > 0.05); the range was 0-7.5% (n = 8 treatments). The average feed conversion ratio (FCR; feed input per unit weight gain of wet abalone) for all diets was 1.19 (r: 0.93-1.4) when uncorrected for uneaten diet, and 0.90 (r: 0.80-0.96) when corrected. The apparent availability of CaCO3 was 65.6%. These results suggest that abalone do not require high levels of Ca in their diet (< 0.5%). Supplementation with CaCO3 is unnecessary, but P supplementation (≤0.7% total P) can improve growth rates. The Ca:P ratio of feed is not important within the range assessed (0.72:1 to 2.68:1). Further research on the effect of greater P supplementation on growth rate and the treatment of plant ingredients to liberate P bound by phytate is required.