Studies On The Biology Of Exotic Fishes In Chabalang Wetland And Their Stresses On Native Fishes

The native fish resources of Chabalang Wetland, one of the main wetlands in the middle and lower reaches of Lhasa River, has undergone serious threaten due to the appearance of plenty of exotic fishes. In order to understand the current resource conditions of Chabalang wetland, investigations on fishes and aquatic organisms there were carried in April2009and April2013. Age and growth of main exotic fishes there such as Pseudorasbora parva, Hypseleotris swinhonis, Carassius auratus and Misgurnus anguillicaudatus were studied. Diet compositions of P. parva and H. swinhonis as well as relationships between native fishes were analyzed. Adaptabilities of these exotic fishes after invading water bodies in the Qinghai-Tibet Plateau were studied by comparing with populations in origin habitat, stresses that exotic fishes to native fishes were disscussed. The main results are as follows:1. Fishes in Chabalang Wetland of2009were mainly exotic fishes, a tiny minority of native fishes mainly triplophysa and schizothoracinae remained. However, in2013the native fishes were disappeared, exotic fishes completely occupied the habitat with the dominance of P. parva, H. swinhonis, C. auratus, M. anguillicaudatus, Paramisgurnus dabryanus and Abbottina rivularis. Exotic fish invasion has being very serious in Chabalang Wetland.2. The maximum age observed for P. parva and H. swinhonis were5year and3year respectively, a little prolonged comparing with native populations, age structure of C. auratus was roughly the same as native while the dominant age of M. anguillicaudatus was larger, these may be connected with the small fishing pressure in the wetland; Calculating from back-calculated total length, the von Bertalanffy growth functions were Lt=107.96(1-e-0.2258(t+1.1150) for P. parva, with growth inflexion point was4.0year and Lt=264.60(1-e-0.1328(t+2.0860) for M. anguillicaudatus, with growth inflexion point was6.4year; Because of the variable climates and low water temperature fishes in the Qinghai-Tibet Plateau grow slowly, especially for the cold and long winter, time for fish to grow fast are short, growth indexes and rate for these exotic fishes were lower than that of the native.3. In the investigation,70genera,8phyla of phytoplankton were collected, among which the species and individual of chlorophyta were highest and biomass of bacillariophyta was the most;30genera,8phyla of zooplankton were collected, among which the species and individual of rotifer and protozoa were highest and biomass of copepod was the most;86genera,12phyla of periphyton were collected, among which the species of chlorophyta was most followed by bacillariophyta; species of zoobenthos was less, and density and bio mass of chironomid larvae and tubificidae were higher. Located in the main agricultural area, affected by agricultural irrigation, sewage discharge and grazing etc., the water of Chabalang Wetland showed corresponding characters demonstrating certain eutrophication.4. Feeding habits of P. parva in Chabalang Wetland was omnivore stressing on animality, chironomid larvae and bacillariophyta were the main food item. The food overlap indexes (morista’s overlap index) between P. parva and native fishes S. o’connori and S. y. younghusbandi were higher. H. swinhonis was carnivore mainly feeding on chironomid larvae and copepod, there was some overlap between H. swinhonis and native fish O. stewartii on chironomid larvae. On account of the difference of habitats of exotic fishes and adult native fishes, impacts that exotic fishes on adult native fishes were limited, while impacts that on young native fishes should arise enough concern.