Dietary total phosphorus requirement of juvenile yellow catfish Pelteobagrus fulvidraco

The present experiment was conducted to determine the dietary total phosphorus requirement of juvenile yellow catfish Pelteobagrus fulvidraco. Six diets with increasing dietary phosphorus concentration (0.43, 0.55, 0.78, 0.90, 1.05 and 1.18% of dry matter, respectively) were fed to triplicate groups of 20 fish each (mean initial body weight, 2.68 ± 0.08 g, mean ± SD) to apparent satiation for 7 weeks. Weight gain and specific growth rate (SGR) increased with increasing dietary phosphorus level from 0.43 to 0.90% and then declined over dietary phosphorus level of 0.90% (P < 0.05). Phosphorus retention increased with increasing dietary phosphorus level from 0.43 to 0.55% and then declined over dietary phosphorus level of 0.55% (P < 0.05). Dietary phosphorus levels significantly influenced whole body crude protein and ash contents (P < 0.05), but not whole body lipid content (P > 0.05). Vertebrae phosphorus content increased with dietary phosphorus level from 0.43 to 0.78% (P < 0.05) and then plateau over the level of 0.78% (P > 0.05). Dietary phosphorus level significantly influenced condition factor, viscerosomatic index and hepatosomatic index (P < 0.05). The relationship between SGR and whole body ash content against dietary phosphorus levels could be expressed as a second-order polynomial equation and the points of 0.89 and 0.85% were considered to be the optimal dietary total phosphorus level, respectively. Based on broken-line analysis of vertebrae phosphorus content, the minimal dietary total phosphorus requirements for maintaining maximum phosphorus storages were estimated to be 0.76% phosphorus.