Wutiporn Phromkunthong and Jacques Gabaudan

pp. 731 - 743

Abstract

Sex-reversed red tilapia of average initial body weight 5.5 g were fed seven practical diets containing 0, 500, 1,000, 2,000 and 4,000 units of microbial phytase/kg and two diets containing 0.2 and 0.3% feed grade dicalcium phosphate (DCP) (but no microbial phytase), respectively. The experiment was carried out in 235-l glass aquaria filled with 180 l water and attached with a closed-recirculating water system with 0.8 l/min flow rate. The experimental period was 10 weeks. All experimental diets were formulated with plant-based
protein of 30% and 6% fat. Results indicated an improvement in apparent digestibility coefficient of phosphorus (ADCP) in fish given phytase supplemented feed. There was no difference in ADCP when 1,000 unit
phytase/kg diet or higher phytase levels (2,000 and 4,000 unit phytase/kg diet) or 0.2 and 0.3% DCP were supplemented. A significant increase was noted for hemoglobin in tilapia that received 1,000 unit phytase/kg diet or higher levels compared to the control. Serum phosphorus markedly increased when the fish were given feeds with 1,000 unit phytase/kg diet and over, while the supplementation of 500 unit phytase/kg diet and over increased serum zinc level. Higher levels of phosphorus were retained in bone whereas lower levels
of phosphorus presented in the feces of tilapia fed feeds supplemented with phytase. Growth performance was markedly influenced when the fish were given feed with 4,000 unit phytase/kg diet.