中文摘要：

运用8种网目规格的成套浮性刺网作为鱼类采样工具,于2005年夏季在长江中游浅水草型湖泊牛山湖进行鱼类定量采样,通过比较不同茂密程度黄丝草生境中的小型鱼类组成、数量和大小结构,探讨此类湖泊小型鱼类的空间分布特征及其与沉水植被的关系.采样期间共捕获13种1124尾鱼,依据其等级丰度和出现频次,和红鳍原!为该湖优势上层小型鱼类.在调查的沉水植物生物量范围内,鱼类物种丰富度和Shannon多样性指数与沉水植物生物量之间呈现倒抛物线关系;两种优势小型鱼类的种群丰度均与沉水植物生物量有着显著的线性正相关关系,且其平均个体大小在裸地生境较高、沉水植被茂密区较低,幼鱼更倾向群聚于厚密的黄丝草生境中;其他生境因子（水深和离岸距离）对和红鳍原!空间分布的影响不显著.黄丝草植被生境是牛山湖两种优势小型鱼类的重要保护生境,应加强对黄丝草等沉水植被的保护及恢复.

英文摘要：

By using a set of pelagic gillnets with eight mesh sizes,an investigation was made on the spatial distribution of small fishes in submerged macrophyte habitats in a shallow macrophytic lake（Niushan Lake） in the middle reach of Yangtze River in summer,2005.The fish composition,abundance,and size structure were examined along a biomass gradient of the most dominant submerged macrophyte Potamogeton maackianus.A total of 1124 individuals from 13 fish species were caught during the study period.According to the abundance and occurrence,sharpbelly Hemiculter leucisculus and redfin culter Cultrichthys erythropterus were identified as the two dominant small pelagic fishes in the lake.There existed dome-like relationships between the fish species richness and Shannon diversity index and the submerged macrophyte biomass within its observed range.For the two dominant small fishes,their abundance was significantly positively correlated with macrophyte biomass,and the average sizes of the individuals of H.leucisculus and C.erythropterus were larger in un-vegetated habitat but smaller in heavily vegetated habitats,indicating that the young individuals tended to live in dense submerged macrophyte covers.Other two habitat factors,i.e.,water depth and distance to shore,had little effects on the spatial distribution of the two fish species.It was inferred that P.maackianus cover should be the important refuge habitat for the two dominant small-sized fishes in Niushan Lake,and it would be necessary to protect or restore the submerged macrophyte covers including P.maackianus.