Studies On Community Composition And Feeding Ecology Of Fish In The Littoral Zone Of Mayliang Bay, Taihu Lake

Fishes were sampled with a trap once half month in the littoral zone, 100m off shore in Mayliang Bay, Taihu Lake, from Sept. 2004 to Nov. 2005. Tweenty-five species of fish were captured and belonged to 24 genera in 9 families of 7 orders in a whole year's sampling. Cyprinus carpio, Carassius auratus, Hemiculter leucisculus, Coilia nasus, Acheilognathus chankaensis, Pesudorasbora parva, Cultrichthys erythropterus were the major fish species. Some feeding indexes of the food composition were computed by analyzing the gastric content (i.e. percentage by number, percentage by weight, percentage frequency of occurrence, the percentage index of relative importance and the selectivity index) . Food composition, seasonal variation of diets and the selective indexes of major foods of three fishes H. leucisculus, C. nasus, C. erythropterus were studied in this study. And more than 20 fish species made a food web according to their feeding copposition.The results showed that the middle and small cyprinid fish were the major species in the Mayliang Bay, including C. carpio, C. auratus, H. leucisculus, A. chankaensis, P. parva, C. erythropterus, which accounted for 89% in the total fishes' biomass. Each fish specie biomass had two peaks in a year. One was in spring or summer when fish spawned, and another was in winter. Many fishes selected the littoral zone to overwinter.H. leucisculus usually preferred Daphnia sp., Bosmina sp., aquatic insects and young fish for food. C. nasus usually preferred to feed on Cyclops vicinus and young fish. C. erythropterus usually liked to feed on Daphnia sp., Bosmina sp. and young fish.And other fishes could be divided into six types: Herbivores ( including Hypophthalmichthys molitrix, A. chankaensis, Hemiculter bleekeri, Ctenopharyngodon idellus) , Omnivores (including Abbottina rivularis, Hyporhamphus intermedius, C. carpio, C. auratus) , Zooplanktivores (including P. parva, Toxabramis swinhonis, Aristichthys nobilis) , Piscivores (including Pelteobagrus fulvidraco, Channa argus, Silurus asotus) , Benthivores (including Sarcocheilichthys nigripinnis, Rhinogobius giurinus) , Detritivores (including Odontamblyopus rubicundus) .The food composition of fish changed in the different growing stage, for example, the adult individuals of C. nasus (total length above 12cm)preferred young fish, shrimps and aquatic insects for food, whereas its juveniles preferred to feed on zooplankton (total length under 12cm) . The adult fish feed bigger foods than juvenile in order to avoid competing with their juveniles.Feeding intensity of fish also changed with seasons. The average of repletion index of C. nasus was 20.96 in the whole year and it was 50.10 in spring, and declined to the lowest 3.00 in winter. So did the feeding rate. The changes of repletion index of H. leucisculus and C. erythropterus was just like C. nasus, highest in spring, and declined...