长江中下游流域刀鲚(Coilia nasus)生态表型的划分

Classification of ecomorphotypes of Coilia nasus from the middle and lower reaches of the Yangtze River Basin

长江流域是我国刀鲚(Coilia nasus)分布的重要水域.传统意义上认为,刀鲚存在长颌鲚和短颌鲚2种表现型,其上颌骨的长或短是区分刀鲚溯河洄游、淡水陆封(湖鲚)和淡水定居3种生态型的关键外形指标.然而这种主观分型经验尚需要野外调查数据验证.本研究基于以往研究所获溯河洄游和淡水栖息刀鲚不同的耳石微化学图谱技术,首先对采集自长江中下游及附属湖泊的刀鲚群体共566尾个体有无溯河洄游“履历”进行了分析确认;再对其上颌骨长、头长、全长进行方差分析和回归分析.结果发现长颌鲚、短颌鲚在早期发育阶段,长、短颌特征分化并不明显.当发育至幼鱼阶段时,前者上颌骨长会长于头长;而后者全生活史过程中上颌骨长均短于头长.发育至幼鱼阶段可能是刀鲚长、短颌鲚分型的临界生活史阶段.此外,长颌鲚中同时存在溯河洄游和淡水定居两种生态型个体,其上颌骨长/头长比值(S/H)分别为1.170±0.075和1.165±0.064,两者S/H比值与形态上同为长颌的湖鲚比值(1.178±0.087)无显著性差异.短颌鲚亦同时存在溯河洄游和淡水定居两种生态型个体,两者的S/H比值分别为0.922和0.918±0.062,与上述3类长颌鲚的S/H比值均差异极显著.因此,建议把长江干流及太湖、鄱阳湖、洞庭湖等水域内3种传统生态型的刀鲚细分为溯河洄游型、淡水定居型长颌鲚,溯河洄游型、淡水定居型短颌鲚以及陆封型湖鲚5种生态表型.

The Yangtze River basin is one of the most important habitat for the long supermaxilla(LS)and short supermaxilla(SS)phenotype estuarine tapertail anchovy Coilia nasus in China.Apart from the ecotype of anadromous migratory(AM)C.nasus(with LS),there are two different ecotypes of freshwater resident(FR)type C.brachygnathus(with SS)and landlocked(LL)type C.nasus taihuensis(with LS),which are traditionally believed to be discriminated in accordance with the length of supermaxilla.However,this subjective experience still needs to be confirmed by the field survey data.Therefore,in the present study the ecotypes assumed by supermaxilla approach of 566 different morphotypic C.nasus from different section in the Yangtze River and affiliated lakes in the middle and lower reaches of the Yangtze River Basin were discriminated by the otolith microchemical maps for AM and FR C.nasus obtained in our previous studies at first.Then,the length of supermaxilla,head and total body of the corresponding fish were comparatively studied.The results showed there were no significant differences between LS and SS types during their early development stage.However,the length of supermaxilla of the former would be longer than that of head when developed to the juvenile stage although that of the latter was still shorter than the length of head.Actually,the LS phenotype anchovies included two ecotypes of AM and FR individuals.The corresponding length ratios of their supermaxilla to head(S/H)were 1.170±0.075 and 1.165±0.064,respectively.Both of them had no significant difference from those of LL C.nasus taihuensis(1.178±0.087)also with long supermaxilla.Likewise,the SS phenotype anchovies could consist of both AM and FR ecotype individuals.However,the S/H ratios of AM and FR types were 0.922 and 0.918±0.062,respectively,which were significantly shorter than those of the aforementioned three LS phenotype anchovies.Thus,it might be better to classify C.nasus resources in the Yangtze River,Lake Taihu,Lake Poyang and Lake Dongting from traditional 3 ecotypes to 5 ecomorphotypes(i.e.,AM and FR LS C.nasus,AM and FR SS C.nasus,and LL LS C.nasus taihuensis).