| Located in the junction of Jiangsu Province, Zhejiang Province and Shanghai Municipality, 31°04'—31°12',120°01',Dianshan Lake is the biggest freshwater lake in Shanghai. It has great many functions in transportation, irrigation, aquaculture, and flood storage, playing a significant role in people's life and economic development.In recent years, the number of aquatic species declined with some species which could reflect the water quality even disappeared. The traditional economical fish stock is also destroyed and the entire population structure of ecosystem of Dianshan Lake has had great changes. In order to protect the environment and maintain ecological balance of water field, Shanghai Municipal Government spent lots of manpower, material and financial resources on fishery enhancement and releasing activities in Dianshan Lake. Silver carp and bighead carp are the main releasing species. It played positive effect on enhancing the fisherman income , promoting the waters ecological remediation and protecting fishery resource.Many problems still exist in Dianshan lake, such as stock depletion and over-fishing. Therefore, based on survey data during 2006~2010, community structure of fishery resources of Dianshan lake was studied and the biology of main economic species was also systematically studied, providing the scientific basis to future research work and providing support to the sustainable development of fisheries resources.The results show that: A total of 18116 fish individuals, representing 41species from 9 orders,18 families and 35 genera, were collected in Dianshan Lake from June 2010 to March 2011, which included 10 surveys by gill net and 10 by trawl net.The most of fish species belonged to Cypriniformes, which account for 47.82% of total samples captured. The dominant species are Coilia ectenes, Acheilognathus taenianalis and Ctenogobius giurinus, accounting for 32.52%,20.26% and 16.45% of total samples respectively. Campared with several historical surveys, the number of species was dramatically declined, but more than survey in 2006 . Fishes showed miniaturization significantly. Overfishing of fishery resource and fishery enhancement and releasing activities are potential underlying reasons for observed shifts in the fish population.Shannon-wiener biodiversity index of March 2011 and July 2010 were higher while January 2011 was lower. Evenness index and dominant index had little variation. In whole , biodiversity index decreased with month from June 2010 and were least at January 2011,then showed a rising trend.There were were prominent differences in biodiversity index between seasons. There was no significant difference in diversity index at each area, that is the even spatial distribution of fish in Dianshan Lake.Gillnet has a strong selectivity and the mesh size has a great influence on catch.Through contrast study, we discover that the bigger the mesh size , the less on species and number by captured. Diversity index and abundance index decreased with the mesh size. Economical species Hypophthalmichthys molitrix and Aristichthys nobilis were mainly caught by the gillnets with 8cm and 10cm mesh sizes while much less in 4cm and 6cm. The mesh size of gillnet should be controlled strictly.Compared with other water areas, growth speed of Hypophthalmichthys molitrix and Aristichthys nobilis in Dianshan lake was slower. the large scale fish releasing, trawl fishery and ecological environment changes were main reasons for the slower growth speed. Hypophthalmichthys molitrix and Aristichthys nobilis mainly feed on Cyanobacteria. Fat degree of Hypophthalmichthys molitrix and Aristichthys nobilis in summer were higher, so enhancement and releasing could help to prevent the occurrence of Cyanobacterial water bloom.The catch rates of Hypophthalmichthys molitrix and Carassius auratus both decreased with month and showed monthly change evidently, which had enormous relations with fishing and season. The catch rates of Cyprinus carpio and Aristichthys nobilis were always lower and had no obvious change in month.In order to make good management and use of fishery recource of Dianshan Lake, fishing operation structure should be adjusted, closed fishing zone,closed season, the management of fishing gear and fishing method should be strengthened. It is imperative to limit fishing strength and to exploit them reasonably to realize sustainable development. |
