Fluctuation of Sr /Ca in otoliths of Coilia nasus in the Yangtze River and the validation for the anadromous migratory history

Coilia nasus long jaw estuarine tapertail anchovy is an important migratory fish in the Yangtze River. Shortjaw grenadier anchovy has long been thought to only live in freshwater,while there is no evidence for whether it experienced an anadromous migration,which has been an ecological puzzle for it is difficult to distinguish by morphological and molecular biology methods. Otolith element fingerprint could specifically and objectively reflect the environment type which fish had lived in,and the element Sr and Ca microchemistry patterns have been always used to replay the environment type which fish has been experienced. Even one sample is used,its experienced environment type could be effectively replayed. To confirm whether there is anadromous long jaw estuarine tapertail anchovy Coilia nasus in the Yangtze River,an electron probe microanalyzer( EPMA) was applied to analyze the element Sr and Ca microchemistry patterns in otoliths for one short jaw grenadier anchovy( XGC-A) and one long jaw grenadier anchovy( XGCB),which were collected from Jingjiang Section of Yangtze River on April 27,2013. Meanwhile,experimental and computational data were compared with the anadromous estuarine tapertail anchovy Coilia nasus. Results of line transect analysis showed a complex Sr /Ca ratio pattern in XGC-A and XGC-B,including a low ration [( 1. 59 ± 0. 80),( 1. 55 ± 0. 74) ]responded to freshwater life,and a high ration[( 4.38 ±1.33),( 3. 56 ± 0. 94) ]responded to seawater life,which suggested that both of them had experienced an anadromous migration. All these differences could be well confirmed by the results of X-ray mapping analysis of EPMA. Results of the microchemistry patterns obtained by both the line transect and mapping analyses confirmed objectively,for the first time,the coexistence of anadromous forms of the shorter supramaxilla estuarine tapertail anchovy C. nasus in the Yangtze River. These afore-mentioned microchemistry patterns will provide impotant information not only for the resources evaluation and protection,but also for the farming plan and future guide in C. nasus. This research provides an important basis for further understanding of short jaw grenadier anchovy life history and Coilia classification.