THE HABITAT HISTORY OF COILIA NASUS IN DAYANG RIVER BASED ON OTOLITH MICROCHEMISTRY

The main economic fish species in Liaoning Province of China, the resource of Coilia nasus has sharply declined in recent years, and currently only small-scale fishing flooding can be seen in the Dayang River. In order to reconstruct C. nasus habitat history, an electron probe microanalyzer (EPMA) was used to analyze the Sr and Ca microchemistry patterns in otoliths of 20 C. nasus collected from the lower reaches of Dayang River in July and September 2020. Results of line transect analysis showed that the samples of C. nasus were of freshwater origin, and the Sr/Ca ratio of freshwater habitats were (1.49±0.61—2.75±0.53). The value of freshwater coefficient (Fc) in the C. nasus is between 0.08 and 0.52, and the diameter of the freshwater area is between 150 and 900 μm. After entering the second change stage, the habitat history fluctuates significantly. The change of Sr/Ca ratio divided C. nasus into three types: (1) C. nasus overwintering in medium and high Sr/Ca ratio areas (brackish water or seawater), and migrates upstream to low Sr/Ca ratio areas (freshwater) during breeding season; (2) C. nasus live in medium and high Sr/Ca ratio areas for a long time without anadromous migration; (3) C. nasus were transformed for many times in the middle high Sr/Ca ratio areas and low Sr/Ca ratio areas, and DYH05 and 19 individuals completed the transformation for up to 9 times. The Sr content analysis result is also the same as the Sr/Ca ratio above. These three types intuitively reflect the upstream migration habits and habitat history characteristics of the C. nasus population in natural water bodies with different salinity levels, in order to provide a theoretical basis for scientifically and accurately grasping the living habits of C. nasus from the Dayang River, formulating strategies for protecting resources and habitats restoration of C. nasus from the Dayang River.