Abstract:Coilia nasus is among the “flagship species” of migratory fish within the Yangtze River. Although lakes such as Dongting Lake and Poyang Lake once served as spawning grounds for C. nasus, the migratory paths of these fish have now been obstructed and the spawning grounds have been lost, as a consequence of factors such as water pollution, overfishing, and the destruction of migratory channels and conservation areas. As a repercussion of these effects, since the beginning of the previous century, the Yangtze River population of C. nasus has been characterized a phenomenon of low age and miniaturization, and there has been a marked overall decline in fish stocks. However, despite these declines in fish status and stocks, in response to the implementation of a 10-year ban on fishing, the declining trend in C. nasus resources has been contained to a certain extent, and populations have gradually recovered in Poyang Lake. In this study, with a view toward confirming the potential ecological function of waterbodies as C. nasus habitats, and thereby provide basic data for an evaluation of the effects of the Yangtze River 10-year fishing ban, we applied otolith microchemistry technology to reconstruct the life history of 20 C. nasus individuals collected during the investigation of these fish in waters of the Poyang Lake region around Xiyuan Town, southern Duchang County, Jiangxi Province. Based on the findings of this study, we provide a theoretical basis for C. nasus resource conservation and habitat protection in Poyang Lake. In this context, some scholars have proposed that the developmental maturity of fish gonads can be used as a means of identifying spawning grounds. Accordingly, among the analyzed fish, zx01, zx04–08, zx11, zx13, zx17, and zx18 can be classified into a spawning group according to sexual maturity, whereas the zx02, zx03, zx09, zx10, zx14–16, zx19, and zx20 fish can be classed as non-spawning. The results of otolith microchemical analysis revealed a high variability in the Sr/Ca values of all otoliths, with low values corresponding to freshwater habitats (Sr/Ca×103 ＜ 3), median values indicative of brackish habitats (3 ＜ Sr/Ca×103 ＜ 7), and high values corresponding to marine habitats (Sr/Ca×103 ＞ 7). The results also revealed that all individuals were typical anadromous C. nasus. Moreover, we not only identified individuals at reproductive stage Ⅲ, but also those with high gonadal development reaching stage Ⅳ. Combined with the analysis of environmental factors in the sampled water areas, we established that the water in the surveyed area was of sufficient quality to serve as a spawning ground for C. nasus. Consequently, we speculate that this water area might be an unreported spawning ground for migratory C. nasus in Poyang Lake, and could serves the ecological function of a C. nasus migratory channel. Furthermore, to briefly analyze the potential associations among different C. nasus populations, we also introduced the concept of the freshwater coefficient. In this regard, we speculate that there may be a close association between C. nasus in the Anqing section of the Yangtze River and C. nasus in local waters, although further investigations are needed to obtain basic data. Our findings in this study also indicated that the C. nasus population in the waters of Duchang County is a composite anadromous population with two migratory patterns. The zx01–08, zx10–15, and zx17–19 individuals were found to be characterized by one of these migratory patterns, whereas the zx09, zx16, and zx20 fish were found to have the second pattern. These findings thus tend to indicate that C. nasus has a strong ability to adapt to different habitat types. In this study, we reconstructed the migratory history of C. nasus in the waters of Xiyuan Town and revealed the migration patterns of this fish. Our findings provide evidence to indicate that this water area is of considerable significance to the replenishment and restoration of the Yangtze River C. nasus resources, and plays an indicative role in evaluating the effects of the Yangtze River fishing ban. These findings accordingly emphasize the importance of protecting this water area from human activities and habitat destruction.
