CURRENT STATUS OF FISH ASSEMBLAGES IN YIBIN REACHES OF THE YANGTZE RIVER

An investigation of fish resources was conducted for four months in 2011,including May to July and October in Yibin reaches of the Yangtze River.A total of 62 fish species,representing 4 orders,10 families,and 40 genera,were collected,in which 19 species were endemic to the upper Yangtze River.The indices of relative importance result showed that 9 species were dominant in the fish assemblage,namely Coreiusguichenoti,Pseudobagrusvachelli,Carassiusauratus,Leptobotia elongate,Botiasupercilliaris,Silurusmeridionalis,Coreiusheterodon,HypophthalmichthysmolitrixandSilurusasotus.Considering ecological type,41 speciesweredemersal fishes,accounting for about 82.26% of all the species,38specieswereomnivorous fishes,accounting for about 62.90%,20 specieswerefishes with spawning drift eggs,accounting for about 32.26%,and 17specieswerefishes living in the torrent water,accounting for about 30.65%.Compared with data of 1997-2005,the percentage(82.26% and 62.90%)of the number of former twospecies above mentionedshowed anincreasing trend relatively,but the other two showed decreasing trend.The phenomenon resulted from changing of ecological environment madequantityof predator on upper trophic level descend.Because most of the demersal fishes were omnivorous fishes whose feeding niche was large and diet was various,they adapted well to new environments which at last led to percentage of the number of species increase.In other words,carnivorous or herbivorous fishes owned simple dietary recipe resulting in easily-damaged population structure,which finally led to decreasing population.A conclusion can be reached that the number of species of fishes with spawning drift eggs and fishes living in the torrent water in Yibin reaches of the Yangtze River would continuegoing down.Compared with past data,averagelength and weight of the main commercial fishes decreasedsharply and yields per fishing boat declined as well.This investigation is the last analysis of the population of structure in Yibin reaches before impoundment of Xiangjiaba,and the results can be referenced to analyze the potential influence of Xiangjiaba Reservoir on the fish resources of the upper Yangtze River and finally provide scientific basis for protecting and managing the fish resources of the Yangtze River.