Phosphorus requirements of African catfish, Clarias gariepinus, based on broken-line regression analysis methods

Phosphorus (P) is a critical nutrient vital for growth and buffer systems in the blood. However, excess supply can lead to toxic effects in fish and eutrophication and pollution problems in the culture environment. African catfish (Clarias gariepinus) juveniles were fed diets containing different levels of inorganic phosphorus supplements to determine its optimum requirements for fish growth. Eleven diets were used. Their P content varied from 3.9 g/kg diet (for the basal diet) to 13.5 g/kg diet. Weight gain, specific growth rate, feed conversion ratio, carcass protein, and fat improved significantly from fish fed without supplemental P to fish fed 8 g P/kg and then declined consistently in fish fed with a diet supplemented with larger amounts of P. The P and Ca contents of the fish whole body increased significantly and showed linear relationship with increasing dietary P levels, whereas the Mg and Zn contents of the fish indicated a decreasing trend. Broken-line analysis based oil specific growth rate and total dietary P contents was used to determine the P requirement for the fish. Quadratic-linear method indicated an optimum P requirement for the growth of the fish as 8.20 g/kg. Quadratic-quadratic and linear-quadratic methods showed optimum P requirement as 7.00 and 6.70 g/kg, respectively. Therefore the study suggests P of 6.70-8.20 g/kg diet as the requirement for the growth of African catfish of 10.2 g weight.