A nine-week feeding experiment was conducted in flow-through system with gibel carp (43.8 ± 0.2 g) to study the effects of dietary available phosphorus (P) on growth, phosphorous digestibility and intestinal enzyme activities. Seven semipurified diets were formulated to contain 0.8 (the basal), 2.4, 3.6, 6.1, 7.4, 10.1 and 15.8 g available phosphorus kg −1 diet. The results showed that specific growth rate and feed efficiency increased with increasing dietary available P from 0.8 to 7.4 g P kg −1 . Fish body ash increased with increasing dietary available P, while moisture, protein content or energy content had no difference. Total phosphorus waste discharging (TPW) increased with increased dietary phosphorous. Plasma glucose was higher in the fish fed with 7.4 g kg −1 P. Plasma triglycerides was lower in fish fed diets containing 6.1-10.1 g kg −1 P. No significant effects were observed in plasma P and Ca (p > .05). The activities of intestinal amylase, lipase and trypsin showed no difference, while AKP and Na + , K + -ATPase activities decreased with increasing dietary available P. In conclusion, based on the regression between specific growth rate (SGR), P retention efficiency, feed efficiency (FE) and dietary available P, the available P requirements for on-growing gibel carp were 10.69, 8.22 and 6.72 g kg −1 , respectively. in many fish species. In order to acquire enough P, fish have to obtain from the diet because fresh water and sea water are low in P concentration (Boyd, 1971). Phosphorus concentrations in most commercial diets considerably exceed the estimated requirements (Rodehutscord & Pfeffer, 1995). Phosphorus is the first limiting factor for algal growth in fresh water, and the excess phosphorus excreted from cultured animals into water can stimulate eutrophication of water bodies and result in deteriorating water quality (Kim, Kim, Song, Lee, & Jeong, 1998). So it is essential to precisely determine the dietary P requirement in order to minimize excess P without risking P deficiency in cultured fish.
K E Y W O R D SThere have been many studies regarding the P requirements for different fishes; the dietary phosphorus requirements for fish species have been reported to range from 3.0 to 15.0 g kg -1 of diet (NRC, 2011). But most studies were focusing on small fish and there is few detailed information about available phosphorus requirements for on-growing fish. Studies have been reported, 5.8 g kg -1 available P for juvenile catfish (Clarias leather) (Yu et al., 2013), 3.0 g kg -1for on-growing catfish (Ictalurus punctatus) (Eya & Lovell, 1997), no information on the available phosphorus requirement for on-growing gibel carp. Therefore, the present study was designed to determine the dietary available phosphorus requirement for on-growing gibel carp and to investigate the effect of dietary P levels on growth performance, body composition, P bioaccumulation and the intestinal enzyme activities.| 1105 XIE et al. 9.5-10.0 g kg -1 available P for juvenile tilapia (Oreochromis niloticus fe...