Water quality, fish community structure and fisheries resources were investigated during 2002 to 2003 in the deep oligotrophic plateau Lake Fuxian in the subtropic China. The purpose of this work was to study the ecological responses of native zooplanktivorous fishes to the invasive zooplanktivorous fishes in plateau lakes in China, so as to provide scientific basis for conservation and restoration of biodiversity and lake environments. The main results as follows:
Lake Fuxian is an oligotrophic lake with low nutrient status. However, the trophic level showed increase tendency in the last 20 years. Spatially, there were no significant difference in nutrient status between the north and south areas.
During the survey from 2002 to 2003, 42 species of fishes belonging to 18 families were collected and identified. Exotic fishes dominated and comprised over 90% of the total fish yield, whereas the production of endemic fish declined dramatically. Such changes were due to various reasons such as the invasion of exotic fishes, over-fishing, alteration in living environment of endemic fishes and irrational fisheries management.
The crustacean zooplanktons were dominated by copepods (Phyllodiaptomus tunguidus) and small-bodied cladocerans (Bosmina). During March to April, large-bodied cladocerans (Daphnia) were dominant, and the densities of crustacean zooplankton reached the highest (142.28 ind./L) in the north areas in April. During the past decades, there were no significant differences in the community structure of crustacean zooplankton, but dominant species changed obviously: Neutrodiaptomus mariadviagae mariadviagae was replaced by Phyllodiaptomus tunguidus, and the large-bodied picivorous cladocerans Leptodora kindti which was dominant in the 1980s was not found in this survey. The densities of rotifers were higherthan before, with a maximum density of 145 ind./L.
Anabarilius grahami, a fish endemic to Lake Fuxian, dominated the fish community in the lake before the 1980s, but its dominance was replaced by the icefish Neosalanx taihuensis since 1989. The production of the endemic A. grahami declined dramatically from 395 tons in 1988 to less than 1 ton in 2003, meanwhile the production of the exotic icefish increased from 213 tons in 1988 to 1538 tons in 2003. The diet of A. grahami was studied by examining stomaches of 82 individuals and it was found that this fish fed mainly on zooplankton but shifted to benthic and picivorous preys more than before. The diets of N. taihuensis were also composed of small cladoceans and copepods in the whole life, which was affected by the body sizeof the fish. Based on Schoener’s index, there was significant diet overlap between A. grahami and N. taihuensis (D=0.773). Both the diet shift and the increase in the fecundity of A. grahami were due to inter-specific competition posed by the exotic N. taihuensis.