Studies On Growth And Carrying Capacity Of Stocking Paddlefish (Polyodon Spathula) In Reservoir

The biomass, biodiversity and structure of zooplankton community in Jinshahe Reservoir were researched based on the specimens collected quarterly from From November 2006 to August 2007. The potential production of Paddlefish was estimated and the trophic level was analyzed according to the zooplankton in Jinshahe Reservoir. On the basis of the early date research, from August 2008 to May 2009, the float cages were set in the middle of the reservoir and the bait-free experiment in the cages of different density including monoculture of Paddlefish and mixotrophic culture of Paddlefish with Silver carp and Bighead carp were carried. The growth and fish yield in the two culture models had been studied and compared in different densities, with the standing crop of zooplankton and fish potential production supplied by zooplankton, the carrying capacity and the best carrying capacity of Paddlefish in Jinshahe Reservoir were estimated, and some suggestions of Paddlefish cultured in Jinshahe reservoir and other mesotrophic reservoir were given in this paper. The results were as follows:1,There were 90 species of zooplankton in Jinshahe Reservoir. The annual standing corp of zooplankton was 882 ind./L in density and 1.221 mg/L in wet weight. In terms of annual density, the zooplankton of the reservoir was dominated by protozoa (53.3%) and rotifera (44.4%).The density of zooplankton in Jinshahe reservoir was highest in the middlestream and lowest in the downstream, while the average biomass was lowest in downstream and highest in upstream. The density of zooplankton was highest in summer and lowest in autumn(988 and 788ind./L, respectively); however the highest biomass occurred in winter (1.298mg/L) and the lowest biomass occurred in autumn(1.090mg/L). Margalef indices of zooplankton and crustacean zooplankton were 13.1 and 17.3, respectively. Based on zooplankton standing crops, it appeared that the reservoir was in mesotrophic status.2,Paddlefish can adapt to the ecological environment of Jinshahe Reservoir. Compared with Bighead carp, the Paddlefish grows faster and has higher stocking efficiency. The specific growth rates of Paddlefish, Silver carp and Bighead carp which grow normally during the experiment were 0.17%-0.20%, 1.5%-1.6% and 0.14%..3,The mixotrophic culture experiment of Paddlefish, Silver carp and Bighead carp in cages showed that, there was no direct food-competition between Paddlefish and Silver carp, the competition between Paddlefish and Bighead carp was obvious. When the stocking density of Silver carp and Bighead carp were 70 kg/hm~2 and 240 kg/hm~2, there would be no significant impacts to the growth and net yield of Silver carp, however, when the stocking capacity of Paddlefish was controlled in the range of 247-784 kg/hm~2, the growth and net yield of Paddlefish and Bighead carp would be less than the low-density group.4,The standing crop of Silver carp and Bighead carp were 70 kg/hm~2 and 400 kg/hm .The fish potential production of Paddlefish supplied by zooplankton in Jinshahe Reservoir could reach 122.1 kg/hm~2. It's feasible to improve the carrying capacity of Paddlefish by reducing the standing crop of Bighead carp in reservoir. While the standing crop of the Bighead carp in Jinshahe Reservoir declined by 40%, that was when the standing crop was 225 kg/hm~2, the carrying capacity and the best carrying capacity of the Paddlefish was 785 kg/hm~2 and 247 kg/hm~2, respectively. If no Bighead carp were cultured in the Reservoir, the carrying capacity and the best carrying capacity of Paddlefish maybe 903 kg/hm~2 and 413 kg/hm~2, respectively.5,Suggest specification of Paddlefish fingerling is bigger than 0.1 kg, the specification of Silver carp fingerling and Bighead carp fingerling are 0.7 kg and 0.85 kg, respectively. The existing fisheries in a hectare water body in Jinshahe Reservoir can cultivate 81 Paddlefish. If the containing of Bighead carp is reduced by 40% in the Reservoir, 141 Paddlefish with 43 Silver carp and 80 Bighead carp can be cultivated in one hectare body of water, 236 Paddlefish and 43 Silver carp when no Bighead carp was cultured. Considering the cost, production of fish and eco-efficiency, we suggest to adopt mixed culture mode to culture Paddlefish, Silver carp and Bighead carp in Jinshahe Reservoir to adjust the structure of the fisheries. The mesotrophic reservoir can determine the stocking amount by referring to the best carrying capacity of Paddlefish stocking in Jinshahe Reservoir combining with the biomass of zooplankton and the stocking situation of Bighead carp.