The Research On Budget Of N&P In Polyculture Ponds Stocked With Paddlefish (Polydon Spathula)

The American paddlefish(Polydon spathula), one of the largest freshwater fish in the United States, was been introduced to China in1988. Aquaculture history of paddlefish were over20years. The fishes belong to planktivores, and are filter feeders. The growth of paddlefish in reservoirs, ponds and river-lakes is faster than many freshwater fishes and may reflect increased food abundance and availability. Paddlefish can stock with other species. They can be harvested easily with gill nets or by seining. The living temperature of paddlefish is3-30℃in fresh water. Paddlefish, like sturgeon, is highly valued for its grayish-black roe that can be processed into caviar and be valued for their boneless, firm, white meat, and the demand of market is large, so, paddlefish represent many outsanding characteristics as a food and highly valued fish.Paddlefish usually stocks with other aquaculture species in polyculture ponds. There are two types of aquaculture of paddlefish in freshwater ponds:paddlefish as a main culture species, or others as dominant culture species with paddlefish.The recent papers about polyculture of paddlefish mostly focus on technology for paddlefish aquaculture, but an account only concerned variation of water quality and plankton of paddlefish ponds, less on utilization of nitrogen and phosphorus, which none in China.Traditional polyculture in ponds has an important status in Chinese aquaculture, but the most culture species are traditional species and represent low economic value. Now, the management and extensive operation of pond culture is confusing, which easily cause super eutrophication and make water quality keep getting worse. Surplus N&P easily cause severe water pollution in the surrounding area too. According to the similarity of feeding habits of paddlefish and bighead carp(Aristichthys nobilis), this paper, by means of measures of water quality, study on plankton, N&P of feed, fish body and sediments in the small polyculture ponds with deep sediments, which is common in Jianghan Plate, mainly stocked grass carp(Ctenopharyngodon idellus)with herring(Mylopharyngodon piceu), silver carp(Hypophthalmichthys molitrix), bighead carp, bream(Parabramis pekinensis), crucian carp(Carassius auratus), when paddlefish did take the place of bighead carp in ponds, we did the analysis and comparison of budger of N&P, and the results were showed below:The experiment was conducted without water exchange(close system) to determine the effects on the variation rules of water quality in polyculture ponds stocked with paddlefish. During the breeding, water quality was measured. After the experiment, These data suggested that the mean values of transparence in paddlefish treatments were lower than the control, and the mean values of total ammonia nitrogen, nitrate nitrogen, total nitrogen, inorganic phosphorus, total phosphorus in paddlefish treatments were higher than the control(bighead carp polyculture-pond). The total nitrogen and the total phosphorus were worse than Grade III. But, the results of analysis of variance (ANOVA) indicate that the water chemistry variables did not differ significantly(p<0.05) among the treatments, and among the treatments and the control. These indifferences may be caused by difference in ability to switch food items between paddlefish and bighead carp, and in the increase of total suspended solids in4polyculture-ponds.This paper studied the plankton community of fish ponds during April to October in2009. These ponds stocked the Grass carp as the dominant cultured species, while stocking paddlefish as the assistant cultured species. In terms of numbers, the species of Cyanophyta and Chlorophyta dominated the community of phytoplankton during the experiment. However, Euglenophyta was the most important component of the phytoplankton community in terms of biomass. The high day of numbers and biomass of the zooplankton in4ponds were from June to August. However, the numbers and biomass zooplankton in4ponds was at low lever monthly. The results indicated that:the mini-type plankton(mini-type phytoplankton and mini-type protozoa) increased during the experiment; the changes of biomass of Chlorophyta and Euglenophyta in4ponds had significant correlation to N/P; Plankton insignificantly differed between paddlefish culture pond and bighead carp pond.The experiment was conducted to analysis the Nitrogen and phosphorus budgets of4polyculture ponds stocked paddlefish/big head(the control).The main results were as follows:The largest percentage of N and P input were feed,95.88%-98.12%for N, and82.87%-89.36%for P. Among the items of N and P output, the harvest fish comprising 27.90～56.47%of TN output,and35.06%-48.11%of TP output.Uptake by muds represented the major loss of N and P comprising45.77%～64.70%of N output and34.79%～51.57%of P output. After we compared and analysed the utilization of N and P in4polyculture ponds stocked with paddlefish, we found that the treatment pond stocked270hm2with paddlefish is better than others and the control in the utilization rate of N and P, deposited N and deposited P.