Studies On Comparison Of Cultured Ecology And Adjustment Of Stocking Structure Of Fish In Different Reservoirs

Studies on water chemistry, plankton and zoobenthos in reservoirs which are the main research aspects of aquatic ecosystem have played a significant role in the conservation, maintenance and recovery of aquatic ecological environment as well as the sustainable development of fishery resources exploit. The present study was aimed at distribution features of physico-chemical factors, community structure, succession rules, and casual analysis of plankton and zoobenthos of the four reservoirs with different trophic types in Huhei province. Interaction mechanism of phytoplankton and zooplankton, and the influence of environmental factors upon both of them were analyzed as well. The correlation between main physical and chemical factors and plankton and zoobenthos was established by means of gradual regression analysis, CCA and other quantitative ecological ways. Comprehensive assessment on trophic states of the four reservoirs was conducted via the comprehensive Trophic State Index(TSIc). Fish productivity and standing crops of phytoplankton, zooplankton and zoobenthos were calculated based on standing crops of biotic organisms. Adjustment proposal of stocking structure of the four reservoirs was suggested by energy-ecological means and comparison of fish production and economical profits of fishery was conducted before and after the adjustment. The results indicated that:1. The water temperature of all reservoirs ranged from 5.5 to 31.0℃and average value was 16.5℃. The content of DO in each layer was abundant, stable, and no less than 6.5 mg/L, featuring stark spatio-temporal variations. DIN presented obvious horizontal distribution and seasonal variations without layer distribution. There was extreme deficiency in PO3-P content wherein P was the principal restriction factor of trophic minerals. The content of TN in winter was 3 to 5 times to that of spring and summer, which was more than 0.700 mg/L in three reservoirs except Jinshahe reservoir with content of 0.392 mg/L, suggesting that the water body had suffered the pollution of N. The mean value of N/P was about 38.0 with a scope from 7.6-142.6, which was higher than usual. The value of ALK and TH of all reservoirs varied from 1.0-2.6 mmol/L, indicating that all water bodies belonged to soft water. Thermocline with a temperature gap of 10℃was found in the depth of 10 m in all reservoirs. Comprehensive trophic type evaluation on water quality was conducted according to the relative comprehensive Trophic States Index(TSIc) and definitive criterion of trophic type of lakes and reservoirs. The results revealed that Jinshahe reservoir belonged to medium-trophic level, Daoguanhe reservoir eutrophication state, and Xujiahe and Taoyuanhe sites medium-eutrophic types.2. There were 215 species of phytoplankton in the four reservoirs, in which diatom, chlorella, and blue-green algae ranked 1,2, and 3, respectively. Blue-green algae was mostly found in the layer above SD, diatom in the layer between SD and 2 SD, whereas other algae including Scenedsmus and Trachelomonas were mainly found in the layer above 2 SD. Layer distribution of phytoplankton biomass was characterized as SD> surface> 2 SD>3 SD> bottom except surface>SD>2 SD>3 SD>bottom in Daoguanhe reservoir. Content of Chl-a varied from 1.25-2.93μg/L with an annual average of 2.04μg/L in Jinshahe reservoirs,5.31-36.56μg/L and 17.9μg/L in Daoguanhe site,2.64-15.51μg/L and 9.64μg/L in Xujiahe sites, and 13-14.19μg/L and 7.26μg/L in Taoyuanhe site respectively, wherein seasonal variations showed extremely significant difference (P<0.01) between all reservoirs. Simpson diversity index (d) was upper stream>middle stream>downstream without no significant difference (P<0.05) except the highest in middle stream in Xujiahe site. It revealed extremely significant difference (P<0.01) in Shannon-Wiener diversity index (H), Margalef diversity index (D), Simpson diversity index (d) and Pielou evenness index (J) between Xujiahe site and other three sites while there was no significant difference (P>0.05) among Daoguanhe site, Taoyuanhe site and Jinshahe site. Negative correlation was found between TN and phytoplankton with the regression equation of y=-0.33x+2.86, p=0.442>0.05, R2=0.033, R2=0.021,γ=-0.182. Positive correlation existed between TP and phytoplankton with the regression equation of y=19.9x+2.14, p=0.06> 0.05, R2=0.183,R2=0.138,γ=0.478(P>0.05). It was the difference in water trophic levels that attributed to the variations of phytoplankton community structure in the four reservoirs.3. There were 147 species of zooplankton in all reservoirs wherein protozoa, rotifers, cladoceran and copepods accounted for 40.0%,26.7%,20.0% and 13.3% respectively. Shannon-Wiener diversity index (H) and Simpson diversity index (d) was 2.99 and 5.16 in Jinshahe sites, which were higher than those of other sites with extremely significant difference (P<0.01). The two indices were 1.80 and 2.48 in Daoguanhe site, featuring significant difference (P<0.05) to that of Xujiahe site with data of 2.08 and 3.58 and Taoyuanhe site with data of 2.07 and 3.72. Biomass of protozoa and rotifers was positively correlated to COD, TN and TP, but negatively correlated to DO(P<0.01). No pronounced correlation was monitored between biomass of cladoceran and copepods and COD, DO, TN and TP, as a result of low density and remarkable individual difference. Pronounced correlation was (P<0.05) found between dominant species and abundance of zooplankton. Obvious impact was seen of zooplankton upon phytoplankton abundance in Jinshahe site whereas positive correlation (r=0.45) was revealed in Daoguanhe site, and no stark correlation was observed in other two reservoirs.4. There were 38 species(genus) of zoobenthos, wherein oligochaeta (14), aquatic sects(18) mollusca(6) accounted for 36.8%,47.4% and 15.8%, respectively. Dominant species in Daoguanhe site were Limnodrilus hoffmeisteri and Tokunagayusurika akamusi with super resistance to pollution, which was similar to that of Taoyuanhe site, a kind of valley-type reservoir. Some zoobenthos like Tanytarsus sp. and Lauterbornia sp. in non-polluted zone, Aulodrilus pluriseta in P-medium-polluted zone et al. widely spread in Jinshahe site with good water quality where some kinds of mollusks were the trophies in sample collection all the year such as Semisulcospira cancellata, Bellamya purificata, Corbicula fluminea and so on. Limnodrilus helveticus inβ-medium-polluted zone and Procladius sp. inα-pollution zone were the dominant species in Xujiahe site, a kind of medium-eutrophic reservoir. Oligochaeta was negatively correlated to COD (P<0.01) and positively correlated to DO and SD (P<0.05). No pronounced correlation was found between aquatic insects and COD, DO and SD. Negative correlation existed between density and species diversity of aquatic insects and water depth via matrix analysis, to the extent where a more drastic decline occurred below the depth of 10 m. Oligochaeta seemed proportional to the content of TN and TP and TP had a more obvious impact upon zoobenthos than TN. Shannon-Wiener and Margalef biodiversity index of zoobenthos, which were widely employed to assess lake water quality, shall be revised when used in evaluation on water quality of reservoirs. Simposon diversity index was absolutely adoptable in evaluation on water quality of deep reservoirs.5. Sample collection of plankton in multi-layer (no less than 5 layers) was suggested in estimation on fish productivity of reservoirs based on mean values of plankton standing crops. Stocking density and proportion of Hypophthalmichthys molitrix and Aristichthys nobilis were calculated based on standing crops and cibating features of two kinds of fish. The function in fishery production of Hypophthalmichthys molitrix should not be overlooked in hot pursuit of the production of highly-valued Aristichthys nobilis. All stocking proportion (calculated as weight) in the four reservoirs was above 0.6:1,where the two kinds of fish presented good growth.