长江江苏溆浦段2015 年发现中华鲟野生幼鱼的形态和分子鉴定

在葛洲坝下中华鲟(Acipenser sinensis)产卵场连续两年未监测到自然繁殖的情况下,2015年6月在江苏溆浦段发现15尾疑似中华鲟幼鱼。本研究通过形态学和分子生物学方法对该15尾幼鲟进行鉴定。形态学度量结果显示,除1尾个体外,新发现的14尾幼鲟与历史记载的中华鲟野生幼鱼生物学性状完全一致,但其体长和体重低于历史同期出现在该区域的中华鲟。同时采用11个多态微卫星位点,对15尾幼鲟样本和分布于我国的3种鲟鱼,包括30尾中华鲟(A.sinensis)、39尾达氏鲟(A.dabryanus)和33尾施氏鲟(A.dabryanus)进行遗传分析,发现这15尾幼鲟与中华鲟的遗传距离最近(F_(st)=0.039,P0.05),其次为达氏鲟(F_(st)=0.108,P0.05),最远为施氏鲟(F_(st)=0.209,P0.05),从遗传和进化的角度判定该批幼鱼为中华鲟,该结果暗示中华鲟在葛洲坝下游极有可能找到了新的产卵场,为中华鲟的繁殖群体和幼鱼的种群监测提供了依据。遗传多样性分析显示,该批鱼的遗传多样性(SW=1.998)略低于野生中华鲟(SW=1.886),暗示中华鲟幼鱼遗传多样性水平降低,野生亲本的数量仍不容乐观。

External morphology and molecular identification of wild juvenile Acipenser sinensis newly found in the Jiangsu Xupu section of the Yangtze River

Chinese sturgeon (Acipenser sinensis) is a large anadromous fish listed under Category I State protection in China and is critically endangered. This anadromous fish has historical commercial importance and was widely dispersed in the main tributaries of the Yangtze River and the coastal regions of the Qiantang River, Minjiang River, and Pearl River. However, natural populations have declined severely in the last three decades as a result of blocking of the migration route by the Gezhouba Dam. Natural reproduction of A. sinensis was interrupted during 2013-2014 according to the monitored number of fish in the breeding population at the Gezhouba Dam spawning site and catadromous juvenile fish in the estuary. Fifteen juvenile sturgeons were found in the Jiangsu Xupu section of the Yangtze River in June 2015. It is of great significance to evaluate whether these juvenile fish are Chinese sturgeon or hybrid sturgeon; however, few studies have tried to identify Chinese sturgeon among other sturgeons. In this study, we successfully identified and differentiated the newly found juvenile fish from three other sturgeon species endemic to China, including 30 A. sinensis, 39 A. dabryanus, and 33 A. schrenckii. Morphological characters, such as bone lamella, gill rakers, and dorsal rays, of these newly found juvenile fish were consistent with those of Chinese sturgeon. Eleven polymorphic microsatellite loci isolated and characterized in a previous study were used to identify the three sturgeon species. The results showed that the newly found sturgeon in the Yangtze River was closest to A. sinensis (F_st=0.039, P < 0.05) and farthest from A. schrenckii (F_st=0.209, P < 0.05), indicating that these fish were undoubtedly juvenile Chinese sturgeon. The level of genetic diversity (mean number of alleles=9.455; total heterozygosity=0.796; Shannon-Wiener Diversity Index=1.998) of these juvenile Chinese sturgeon was lower than that of other wild Chinese sturgeon (mean number of alleles=13.455; total heterozygosity=0.810; Shannon-Wiener Diversity Index=1.886), suggesting that the size of the wild Chinese sturgeon breeding population is decreasing. No natural A. sinensis reproduction was found during 2014 at the Gezhouba Dam spawning site, which is the only known spawning site for this endangered species. We speculate that these fish came from another spawning ground. In recent years, the Three Gorges Dam, which is the world''s largest hydroelectric project, was put on-line, and it has had a tremendous impact on the natural reproduction of Chinese sturgeon by influencing the seasonal fluctuations in downstream water flow and temperatures, potentially resulting in loss of the eco-hydrological conditions needed by the fish for spawning. The Chinese sturgeon is an adaptable fish judging from its life history, so it is likely that other spawning sites located downstream of the Gezhouba Dam are being used. It is necessary to identify the exact positions of these spawning grounds to describe the hydrological conditions and better protect this endangered species. Our results will be useful for monitoring natural populations, surveying new spawning sites, and designing conservation strategies.