Wutiporn Phromkunthong and Udomnant Udom

pp. 7 - 16

Abstract

A feeding trial was conducted to estimate the optimum requirement of dietary phoshporus (P) for sex-reversed red tilapia in glass aquaria (50x100x47cm). Six practical diets were formulated to contain graded levels (0.58, 0.66, 0.72, 0.75 and 0.82%) of available P from all-plant raw ingredients and dicalcium phosphate (DCP). Each diet was randomly assigned to triplicate groups of fish, and each group was stocked with 20 fish (initial body weight, 25.16g   0.13). Fish were fed twice daily (08:00 and 16:00) ad libitum for 8 weeks. Average body weight and weight gain significantly increased with increasing available P (P<0.05). The whole body composition analysis showed that lipid and protein as well as P contents in whole body, vertebrae ash and vertebrae p, were significantly affected by available P (P<0.05). The blood biochemistry analysis showed that serum P and serum alkaline phosphatase activity increased with the increase of dietary available P levels (P<0.05). Data for weight gain, FCR, whole body P, vertebrae ash, vertebrae P, muscle protein, muscle fat and visceral fat were subjected to regression analysis to determine effects of the dietary levels of available P on these responses. Employing quadratic non-linear regression model of the relationship between available dietary P and P in vertebrae and whole body to study the P requirement, it was found that available dietary P requirement for sex-reversed red tilapia from the current
study were of 0.76 and 0.79%, respectively. Increasing the dietary available P to higher concentration appears to reduce muscle fat while muscle protein increases.