The digestible phosphorus requirement in practical diet for largemouth bass (Micropterus salmoides) based on growth and feed utilization

The present study was conducted to estimate the optimum requirement of phosphorus in practical diets for largemouth bass (Micropterus salmoides). Six iso-energetic and iso-nitrogenous diets were formulated with the supplementation of monocalcium phosphate (MCP) of 0, 5, 10, 15, 20 and 25 g/kg in basal diet containing 350 g/kg fish meal, respectively. The digestible phosphorus of the six diets was measured as 5.7, 6.7, 7.8, 8.7, 9.3 and 10.0 g/kg, respectively. Each diet was randomly fed to triplicate groups of 25 juvenile fish (initial body weight, 16.0 ± 0.2 g) for 60 days. The results showed that weight gain increased, and feed conversion ratio decreased with the increase of dietary phosphorus. When dietary MCP exceeded 15 g/kg (digestible phosphorus of 8.7 g/kg), the WG and FCR were maintained at the similar values. The crude ash, phosphorus and calcium contents in whole body, apparent digestibility of phosphorus and protein retention also increased with the increasing phosphorus level in diets. Vertebrae phosphorus and calcium levels and plasma phosphorus showed no further increase when dietary MCP reached 20, 20 and 10 g/kg with digestible phosphorus of 9.3, 9.3 and 7.8 g/kg, respectively. Broken-line analysis indicated that the digestible phosphorus requirement for largemouth bass were 8.9, 8.7 and 9.6 g/kg based on weight gain, feed conversion ratio and vertebral phosphorus content. In conclusion, the supplementation of MCP in a diet containing 350 g/kg fish meal improved the growth and feed utilization of largemouth bass, and the digestible phosphorus requirement was suggested to be 8.7–8.9 g/kg with MCP supplementation of 15.0–15.8 g/kg.