Otolith microchemistry reveals various habitat uses and life histories of Chinese gizzard shad Clupanodon thrissa in the Min River and the estuary, Fujian Province, China

Abstract

Otolith microchemistry allows reconstructing the life histories and understanding the habitat uses of fishes. In this study, the relationship of Sr:Ca ratios and salinity from various environments, i.e. freshwater of the Min River, brackish water of the estuary and seawater of the coastal marine (Fujian Province, China), were built, revealing a significant positive correlation (p < 0.05). A total of 29 adult Chinese gizzard shad Clupanodon thrissa were collected in 2017–2020 for otolith (sagitta) microchemistry. The specimens were only collected from the Min River and the estuary, with none from the coastal marine regions despite same efforts input. The results confirmed that all 29 individuals hatched in either freshwater or brackish water. Four contingents were recognized based on various life histories, including three migratory contingents (Types A-C, N = 26) and one freshwater residential contingent (Type D, N = 3). The three migratory contingents were the freshwater-brackish migratory contingent (Type A, N = 12), the brackish-freshwater migratory contingent (Type B, N = 10) and the brackish-variable migratory contingent (Type C, N = 4). Only a small proportion of C. thrissa individuals (N = 4) migrated to seawater habitat during the first few months of lifetime, and most individuals preferred freshwater habitat during the first year. There were no significant differences between life history pattern and sex (p = 1.00), and between the number of fish migratory times crossing different habitats and age (p = 0.84). The lower reaches of the Min River and the estuary are confirmed to be important spawning grounds for C. thrissa, based on otolith microchemistry of this study and gonad histology of a previous examination. The findings have significant implications for the Min River and the estuary protection and fishery stock management.