Study on the Nitrogen and Phosphorus Budget and Production Performances in Intensive Pond Culture of Shrimp
|Keywords||Litopenaeus vannamei higher-place ponds water quality nitrogen and phosphorus budget production performances|
The research was taken at the higher-place shrimp ponds of Longma culture base of Zhengrui Aquaculture Co., Ltd in Wenchang city and Bo’ao shrimp farm in Qionghai city of Hainan provience. The growth status of Litopenaeus vannamei, water quality, sediments and nitrogen and phosphorus budget of ponds were studied systematically, according to the different culture modes, culture seasons and shrimp larvae strains. In Zhengrui the shrimp stocking at summer (ZS), fall (ZF), winter (ZW and ZWb), and the shrimp larvae strain were the same first filial generation (Fl) breeded by batches of SPF Litopenaeus vannamei, while in the Bo’ao winter trial (BW), the cultured shrimp larvae was breeded by local selected brood stock. In addition, trial ZWb was piecewise cultured, while others were general cultured.The result showed the total inputs of nitrogen and phosphorus in the shrimp ponds was 808.93-1155.58kg/hm2(N) and 160.08-239.49kg/hm2(P) respectively. Among which the feed was the main source of nitrogen and phosphorus inputs, which accounted for 91.76%-93.68% and 94.55%-96.97%, and water inflow and fertilizer followed by, while the rainfall and shrimp larvae account for only a little.Within the ponds, the nitrogen and phosphorus was converted to harvested shrimp accounted for 29.46%-40.46% and 12.64%-17.41% of the total inputs. The outputs of nitrogen and phosphorus in the form of harvested shrimp were significantly affected by the shrimp larvae strains and culture seasons. When the larvae strain were the same Fl, the outputs of nitrogen and phosphorus in the form of harvested shrimp of the trial ZW were 33.33%-38.46% and 14.39%-16.66% respectively, and the trial ZF were 29.87%-38.44% and 12.78%-16.56% respectively, while trial ZS were 29.46%-31.58% and 12.64%-13.49%. The outputs of nitrogen and phosphorus in the form of harvested shrimp in summer were significantly lower than winter and fall (P<0.05), it may because that the water temperature was higher, which enhanced the respiration of organism, leading to the low survival rate and percentage of nitrogen and phosphorus outputs for the shrimp. The outputs of nitrogen in the form of harvested shrimp of trial BW were 30.18%-36.37%, which were significantly lower than ZW trial (P<0.05). The highest percentage of nitrogen and phosphorus outputs in the form of harvested shrimp were 37.63%-40.46% and 16.21%-17.41%, which was appeared in trial ZWb, while had no significantly difference with the general cultured ZW trial.The production performances were greatly affected by the shrimp larvae strains and culture seasons. Because of the high temperature, the average growth rate of trial ZS reached 0.175 g/d in summer, which was 73.0% and 139.3% higher than the trial ZF in fall and trial ZW in winter respectively. The survival rates of trial ZW was 77.70%-87.75%, which was significantly higher than trial ZS and trial ZF (P<0.05). While in the same culture season, the survival rates of trial BW was 62.10%-72.30% and the yield per unit area was 8821-9878kg/hm2, which was significantly lower than the trial ZW (P<0.05). Trial ZWb which was piecewise cultured shorted the culture cycle by the 56.13%, at the same time, the increase in organic matter of the sediments was 9.41% lower than the trial ZW.The quality of source was in accordance with water quality standard for fisheries (GB 11607-1989). While the dissolved inorganic nitrogen and phosphorus of the water were 7.03 and 6.50 times as much as the eutrophication standard (DIN,0.30mg/L; DIP,0.045mg/L) after the shrimp cultured. Furthermore, the trophic state index (E,3886-6558) and the organic pollution index (A,26.32-30.25) exceeded the high eutrophication standard (E>3.0) and serious pollution standard (A>4.0).The sediment was shown light acidic and it tended to decrease with the culture. The trial ZS with the maximum water exchanged showed the least rate in budget of nitrogen (14.10%-20.85%) and phosphorus (27.59%-38.76%) in the sediments. It was significantly lower than other trials (P<0.05). It could decrease the nutrient loading rates of the water and sediment when increase the quantity of exchanged water. According to the study,59.43kg nitrogen and 15.31kg phosphorus will be released to the environment by effluent discharging and pond sediment washing for one ton of shrimp production.