| Coilia nasus is one of the "flagship species" of migratory fish in the Yangtze River. Lakes such as Dongting Lake and Poyang Lake used to be the spawning grounds of Coilia nasus, but the migration path of Coilia nasus was blocked and the spawning grounds lost due to water pollution, overfishing, destruction of migration channels and conservation grounds, etc. Therefore, the Yangtze River C. nasus has shown a phenomenon of low age and miniaturization since the beginning of the last century, and the amount of population resources has declined sharply. However, with the implementation of the ten-year ban policy, the declining trend of C. nasus resources has been contained to a certain extent, and the C. nasus resources in Poyang Lake have gradually recovered.
This study intends to reconstruct the life history of 20 individuals collected during the investigation of C. nasus from the Poyang Lake region waters around Xiyuan Township of south of Duchang County, Jiangxi Province, using otolith microchemistry technology, in order to confirm the possible ecological function of the waters as the C. nasus habitat, and thus provide basic data for the evaluation of the effect of the Yangtze River ten-year fishing ban. And provides a theoretical basis for resource conservation and habitat protection of C. nasus in Poyang Lake. Some scholars study found that fish gonads development maturity can be used to speculate the spawning grounds. Therefore, individuals (i.e., zx01, zx04~zx08, zx11, zx13, zx17 and zx18 can be classified into spawning groups according to higher sexual maturity (> stage IV), and the remaining individuals (i.e., zx02, zx03, zx09, zx10, zx14~zx16, zx19 and zx20) belong to non-spawning groups. The results of otolith microchemistry analysis showed that the Sr/Ca values of all otolith were highly variable, not only having the low values corresponding to freshwater habitats (Sr/Ca×103<3) and the median of corresponding brackish habitats (3 7), The results showed that all individuals were typical anadromous C. nasus. Moreover, in this study, there were not only individuals with a reproductive degree of stage III, but also individuals with high gonadal development reaching stage IV. Combined with the analysis of environmental factors in the sampled water area, the water area met the suitable conditions for serving as the spawning ground of C. nasus, so it was speculated that the water area might be an unreported spawning ground of migratory C. nasus in Poyang Lake. It also serves the ecological function of the C. nasus migration channel.
The concept of freshwater coefficient was also introduced to briefly analyze the possible associations among different C. nasus populations. We speculate that there may be a close relationship between C. nasus in the Anqing section of the Yangtze River and C. nasus in the local waters, but further investigations are needed to enrich the basic data. The results of this study also found that the C. nasus population in the waters of Duchang County was a composite anadromous population with two migratory patterns. Zx01-08, zx10-15 and zx17-19 belonged to the first migratory pattern, while zx09, zx16 and zx20 belonged to the second migratory pattern. It shows that C. nasus has a strong ability to adapt to different habitats.
This study reconstructed the migration history of C. nasus in the waters of Xiyuan Township and revealed their migration patterns, indicating that this water area is of great significance to the replenishment and restoration of the Yangtze River C. nasus resource, and plays an indicative role in the evaluation of the effect of the Yangtze River fishing ban. It is of great importance to protect this water area from human activities and habitat destruction. |
