| Anqing section of the Yangtze (Changjiang) River in Anhui Province is one of the most important migratory channels and distribution for highly valued diadromous estuarine tapertail anchovy Coilia nasus. In the past decades this section has suffered a severe loss of C. nasus resources caused by human activities (especially overfishing, water pollution). Since 2019 a fishing ban policy for the species on the Yangtze River had launched in China for its resource restoration. Fish otoliths are calcium carbonate structures, and otolith microchemistry can provide detailed life history information that can be used to identify the habitat use experience among different salinity water bodies. In order to explore the habitat history of in the Anqing section of the Yangtze River after the implementation of the fishing ban, we examined the otolith Sr and Ca microchemical characteristics of the long maxillary (once named C. ectenes) and short maxillary (once named C. brachygnathus) types of the fish using the approach of electron probe X-ray microanalysis (EPMA). Results of line transect analysis of Sr/Ca ratio suggested that the short maxillary C. nasus individuals could be divided into two groups. The ratios of otolith Sr/Ca (calculated and expressed as Sr/Ca×1000) of one group were always lower than 3.0, indicating their freshwater resident life history. Those of another group were had two phases of low values (< 3.0, believed to be indicative of a freshwater habitat), and high values (> 3.0, believed to be indicative of a brackish or sea water habitat), indicating that the anchovies had not only freshwater habitat history with low salinity, but also brackish habitat history with high salinity. The latter group of the anchovy was typical anadromous C. nasus, as the Sr/Ca value of the otolith of C. nasus fluctuated significantly and coincided with the variations between freshwater and estuarine brackish or sea waters, i.e., the anchovies once experienced not only the freshwater, but also the brackish water habitats at different stages of their life history. The Sr content mapping analysis of EPMA with different color patterns for freshwater (blue color), brackish (green-yellow color) and sea (red color) water habitats also confirmed the above results obtained from line transect analysis. Our results demonstrated that the population composition of C. nasus in the Anqing section of the Yangtze River became complex, and there was coexistence of freshwater resident and anadromous ecomorphotype C. nasus in Anqing Section of the Yangtze River in Anhui Province, i.e., anadromous and freshwater resident short maxillary and anadromous long maxillary Coilia nasus. This phenomenon might suggest a restoration of C. nasus resource diversity after the implementation of the fishing ban in the section of Yangtze River. |
