Studies On The Present Condition Of Fish Stocks And Its Spatial Structure, Growth Characteristics In Erhai Lake

Erhai is a plateau lake which situated near Dali Cily. Yunnan Province. West Lake. Cibi Lake and Haixihai Lake are located in the upper of Erhai Lake Basin where the lake ecosystem is relatively closed. This thesis reviewed on recent research progress of fish ecology of Erhai Lake, vestigated the fish resource at21sites in the Erhai Lake basin in August and November2009. and studied the fish community structure, spatial structure, growth characteristics and morphological variation based on the data from the survey. The study had veritably reflected the current situation of fish resource in Erhai Lake, and put forward two new fishery-development models for your information. The main results are as follows:(1) Now. the fish fauna of Erhai Lake is similar to that of the lower-middle reaches of the Yangtze River. There are23fish species in Erhai Lake, belonging to6orders and9families. The most abundant family is Cyprinidae with14species. Next is Gobiidae with two species, and any other families has one. The quantity composition shows that the population of Ctenogobius giurinus and cliffordpopei is largest, next was Neosalanx taihuensis. The quality compositon shows the yields of Hypophthalmichthys molitrix and Aristichthys nobilis are biggest, nest are C. giurinus. C. cliffordpopei and N. taihuensis. The yields of original commercial Carassius auratus and Cyprinus carpio are lower. The artificial stocking fishes have become the main species in fishery of Erhai Lake. In the existing23fish species of Erhai Lake, there are only five original species (C. auratus, Misgurnus anguillicaudatus, Monoptenu albus, Oryzias latipes sinensis and Schizothorax tallensis), and the rest19species are all foreign kind. There are five species (C. giurinus, C. cliffordpopei, Pseudorasbora parva, Monoptenu albus and N. taihuensis) have become invasion. A new kind of fish was recorded in this survey which is a high-risk invasive species.(2) The spatial structure of fishes is obvious in Erhai Lake. Each water-course has fast growth, fertility, and adaptable species. The fish community of Erhai Lake can be divided into three groups:alongshore community, open water community and upstream community. The indicator species and environment of each group are obviously different, so is the discriminating species between the three groups. The wetland system along shore was great significance for fisheries eco-development and fish diversity protection in Erhai Lake. (3)Although the foreign fishes in Erhaj Lake are all come from the lower-middle reaches of1he Yangtze River,they have shown good adaptability in the highland environment.Each species grows Well (in uniform growth or nearly uniform growth),and there are no significant difierences belween the growth of fishes living in highland environment and in plain environment.Non-filter feeding fish(C.carpia,C.auratus and Megalobrama amblycephala) have the highest Condition factor,and filter-feeding fish(H. molitrix, A. nobilis) take second place.This also reveals that Erhai Lake was rich in bait,and the fish feeding strong.(4)Eight morphological charaeterristics(TL/BL,BD/BL,BW/BL,HL/BL,HD/HL, HW/HL,ML/HL,ED/HL)of four P. parva populations and four C.auratus populations are analyzed respeclively. There is no sjgnificant difference between P. parva sampled in Erhai Lake and the others；so is C. auratus.But there are inter-population differences among three P. parva populations,which sampled in West Lake,Cibi Lake and Haixihai Lake respectively.So is C. auratus,and lhe difference of ED/HL between C. auratus sampled in Cibi Lake and Haixihai Lake is in Ihe subspecies level.(5)The main fishery model in Erhai Lake was extensive farming model,and the main stocking species were H.molitrix, A. nobilis, M. amblycephala, C. carpio, and C.anratus. And up to now,there was no very effective Solution in control or the wild trash fishes with small size and proliferation of the rare indigenous fish species.The two developmental pattems of fishery are put with different focuses:proliferation of the stocking economic fish species:control of the small size and low value fish species, and restoration of the rare and indigenous fish species; proliferation of the stocking economic fish species, and introduction of new improved varieties.