The Effect Of Dietary Phosphorus Level And Poly-culture On Growth And Water Environment Of Crucian Carp(Carassius Auratus)

Two experiments were conducted to evaluate the effect of dietary phosphorus level and stocking of silver carp and big head carp on growth performance, composition, water quality, phosphorus budget and plankton in intensive culture of crucian carp(Carassius auratus).1. The first experiment was carried out to evaluate the effects of dietary phosphorus levels on growth performance and body composition, water quality,phosphorus budget and plankton composition in intensive culture of crucian carp. Monocalcium was used to formulate extruded feed containing available phosphorus and total phosphorus of 1.5 and 8.7(D1), 4.7 and 11.4(D2), 6.3 and 13.5(D3) and 9.0 and 18.4(D4) g kg-1. 12 polyethylene enclosures were assigned to four groups with each one was stocked with 120 juveniles(44.08�1.36g). After 8weeks of feeding, survival ranged from 96% to 100%. Weight gain, special growth rate, protein efficiency ratio and feed conversion rate did not show significant differences among dietary treatments in both experiments. Fish cultured in the enclosures grew better, though D1 and D2 treatments did not reach significant level. Crude protein and phosphorus content of the fish was not significantly affected by dietary phosphorus level. Moisture, crude lipid, crude ash, and vertebrae phosphorus was significantly affected by different phosphorus levels. Based on vertebrae phosphorus, crucian carp cultured in the enclosures showed phosphorus deficiency under 6.3 g /kg AP. Growth and survive rate of carp was not affected by diet of different P level.It was found that physiochemical factors in all the enclosures didn't show obvious threat on fish.Diets of different P level did not affect dissolved oxygen, secchi depth, total ammonium nitrogen and total nitrogen concentration in enclosures. However, increased P level in diets seemed increased averaged p H, soluble reactive phosphorus concentration, total phosphorus concentration and decreased nitrite concentration and TN/TP. During later experiment time,treatments with high diet P level(D3 and D4 treatments) had very high cyanobacterial biomass dominated. Composition and density of zooplankton in different treatments varied in similar pattern. Peak density of cladocerans(mainly Moina) seemed to be related to diet P level. The present study indicated that changing P level in diets might brought complicated changes to the intensive crucian carp culture ecosystem.2. Monocalcium was used to formulate extruded feed containing total phosphorus of 8.7(LF) and 13.5(HF) g/ kg. 12 polyethylene enclosures were assigned to four groups with each one stocked with 50 juveniles(71.00�0.58g) crucian carp. The experiment groups were assigned as L1, H1, L3 and H3. The fish in L1 and L3 fed with the LF while the fish in the H1 and H3 fed with HF. The groups of L3 and H3 were stocked with 10 silver carps(50.00�0.37g)and big head carps(25.46�0.79g) at the same time. The results show that stocking with silver carp and big head carp would suppress the weight gain rate, specific growth rate, final weight and feed conversion rate of crucian carp while fed the feed with low dietary phosphorus.Different dietary phosphorus had no significant effect on the growth of big head carp, but the silver carp under higher dietary phosphorus show significant better growth performance. The different dietary phosphorus level and stocking with silver carp and big head carp had no significant effect on most water quality parameters such as ammonia nitrogen, total nitrogen and total phosphorus. However, stocking with silver carp and big head carp under higher dietary phosphorus had significant lowest nitrate nitrogen, nitrite nitrogen and dissolve inorganic nitrogen concentration in the water. The phosphorus input of feed was the major kind of phosphorus input, ranged from 47.93 to 63.09%. The dietary phosphorus level and stocking with silver carp and big head carp had significant effect on the phosphorus output of crucian carp and total fish and phosphorus retention of crucian carp and total fish. Stocking with silver carp and big head carp would suppress the biomass and density of phytoplankton and zooplankton as well.