水电站影响下太湖西苕溪鱼类产卵生境及其早期资源与环境因子的关系

水利设施运行影响下的鱼类早期资源发生规律被逐渐关注, 坝下区域也成为鱼类产卵生境的关注热点。西苕溪作为太湖上游的重要补充支流, 是太湖流域鱼类完成生活史过程的重要载体。为解析电站影响下的坝下河流生境变量与鱼类早期资源的内在联系, 本研究于 2022 年 4—7 月在西苕溪江东电站坝下的东山段开展了持续 90 d 的鱼类早期资源调查以及时空格局研究。结果显示, 该区域鱼卵日平均密度为(0.5±0.7) ind/m³, 仔鱼日平均密度为 (0.5±0.6) ind/m³。运用形态学结合分子生物学方法进行种类鉴定, 共鉴定鱼类 35 种, 隶属 4 目 14 科 22 属, 其中产沉性卵鱼类 9 种, 产浮性卵 5 种, 产黏性卵 9 种, 产漂流性卵 12 种。5 月下旬、6 月上旬和 6 月下旬为产卵高峰期。 左右岸样线以沉性卵和以水生植物为黏附基质的产黏性卵鱼类为主, 河心样线则以产漂流性卵、产黏性卵和浮性卵鱼类为主。该区域鱼类卵苗数量受水温、流速、水位影响较大, 水位、流速是影响鱼类繁殖的主要因子, 电站调度对卵苗量有显著影响。基于卵苗收获量、卵苗发育时期等结果, 判定该采样区域——西苕溪江东电站坝下东山段为适宜多种鱼类繁殖的复合型产卵场, 对太湖流域鱼类多样性和渔业资源保护具有重要意义。

Early fish resources and their relationship with environmental factors in Dongshan Reach of the Xitiaoxi River in the Tai Lake

With the construction and operation of water infrastructure in river basins, significant alterations have occurred in the original habitats, leading to changes in the patterns of juvenile fish resources and the spatial distribution of fish spawning grounds. As a result, considerable attention has been devoted to studying the patterns of juvenile fish resources and the characteristics of spawning grounds in various sections of the Yangtze River mainstream. The dam downstream area has emerged as a focal point for investigating fish spawning habitats. However, due to constraints such as hydrological conditions and topography, localized studies on the spatiotemporal patterns of fish spawning and early life stages in the dam downstream area have been challenging. Extensive research has been conducted on the dynamics of fish community structure in the middle and lower reaches of the river, as well as the interconnected lakes, encompassing changes in fish populations and the mechanisms driving river-lake migrations. However, limited research is available on the coupling relationship between concentrated spawning habitats, fish resources early in their life cycle, and river environments in the upstream tributaries of lakes. Exploring the patterns of early-stage fish resources and concentrated spawning in the upstream tributaries of large lakes is equally important for the conservation of aquatic fisheries resources. The upstream rivers of lakes serve as crucial ecological zones for migratory fish reproduction in river-lake systems and play a vital role in replenishing juvenile fish resources for such species. The Xitiaoxi River, an important supplementary tributary of the Tai Lake, also serves as a crucial conduit for fish migration in the southern the Tai Lake basin. It is home to a nationally protected gene pool and boasts abundant fish resources. The East Mountain section below the Jiangdong Power Station in the Xitiaoxi River is a concentrated breeding site for regional fish populations. Moreover, the area downstream of the Jiangdong Power Station provides favorable hydrological and topographical conditions, making it an ideal location for conducting localized studies on the spatiotemporal patterns of juvenile fish resources. To investigate the intrinsic relationship between the variables of the downstream river habitat and fish resources under the influence of the power station, this study conducted a 90-day survey of fish resources and spatial-temporal patterns using a shallow type I plankton net in the Dongshanjiang section of the Xitiaoxi river from April to July 2022. The survey obtained 24455 fish eggs and 24325 larval fish, with a daily average density of (0.5±0.7) ind/m³ and (0.5±0.6) ind/m³, respectively. Using morphological and molecular biology methods for identification, a total of 35 fish species were identified, belonging to four orders, 14 families, and 22 genera. Hemiculter bleekeri, Squalidus argentatus, Cyprinus carpio, Carassius auratus, Saurogobio dabryi, and Culter mongolicus had relatively high numbers of eggs and larvae. The fish resources included 9 species of benthic egg-laying fish, 5 species of pelagic egg-laying fish, 9 species of adhesive egg-laying fish, and 12 species of drifting egg-laying fish. Late May, early June, and late June were the peak spawning periods. The sampling results evidenced that benthic and adhesive egg-laying fish, which use aquatic plants as attachment substrates, were dominant on the left and right bank sample lines, whereas drifting, adhesive, and pelagic egg-laying fish dominated the river center sample line. The redundancy analysis results evidenced that water temperature, flow rate, and water level influenced the number of fish eggs and larvae in the area to varying degrees, with water level and flow rate being the main factors affecting fish reproduction, and egg production increasing significantly after rainfall. Based on the results of egg harvest and egg development stage, the sampled river section and the upstream river of Dongshanjiang in the Xitiaoxi River were determined to be a composite fish spawning ground. The fish resources in this spawning ground were abundant, and the habitat was suitable for fish reproduction and nurturing. The discharge of the power station had a certain effect on fish reproduction, and moderate ecological scheduling could meet the needs of fish reproduction, which was of great significance for the protection of fish diversity and fishery resources in the Tai Lake.