Study On Perch(Perca Fluviatilis Linnaeus) Invaded Mechanism By Alien Fish In Ulungur Lake, China

We studied the variation of ecological environment and Perch (Perca fluviatilis Linnaeus) biology between 1987 and 2007, to reveal this fish invaded mechanism by alien fish in Ulungur Lake. In April and August 2007, aquatic chemistry,biomass of plankton and zoobenthos,distribution of macrophytes,variation of fish community and perch biology were investigated in Ulungur Lake. and the variation of perch population ecology including age structure,growth rate and formula,fullness,sex ratio,gonad development and diet in 20years was studied entensively as main topic.Water chemistry variation was not main reason to Perch endangered via water chemistry investigation. Research of food organism community means great sharp down of biomass, which might lead to food lack of Perch, and Perch grew more slowly and got thinner in the changed environment. By analysis the composition of Perch stomach, we found the diet bias, that madly multiplificated alien Pond smelt (Hypomesus olidus Pallas) became the substitute food of Perch on the condition of preference food Chinronomidae larvae lack. Comparing the diet of Perch and the main carnivorous fish Northern pike(Esox ludus Linnaeus) in the lake, we found there was no food competation between them, and Northern pike do not threaten perch. Investigation of breeding biology in April, turned out all female perch gonad reach to phage II or III, so the gonad development of Perch was blocked and reproduction become the bottleneck of population recruiting.So, we got the conclusion that alien fish such as Pond smelt (Hypomesus olidus Pallas) madly multiplification led to the fish food organisms biomass reduction seriously of the whole lake , and no exception of zoobenthos including preference food of Perch such as Chinronomidae larvae. And the lack of Chinronomidae larvae made Perch choose abundant Pond smelt(Hypomesus olidus Pallas) in the enviroment as the substitute food, which led Perch innutrition,growth slower,thinner and gonad develop slower even fail to reproduct, and the population can not be recruited. In a word, alien fish such as Pond smelt (Hypomesus olidus Pallas) restricted the Perch population development via food competation indirectly.