Characteristics of two populations of Thai river sprat Clupeichthys aesarnensis from man-made reservoirs in Thailand and Laos, with aspects of gonad development

Abstract

© 2019, Japanese Society of Fisheries Science. Growth and reproduction of the Thai river sprat Clupeichthys aesarnensis (Teleostei: Clupeidae) in Sirindhorn Reservoir, Thailand, and Nam Ngum Reservoir, Laos, were investigated using age estimates obtained from daily growth increments in otoliths and gonad observations. This species breeds throughout the year in both reservoirs, although water temperature was higher in Sirindhorn than in Nam Ngum. The Sirindhorn population tended to mature at smaller size (length) and younger age than the Nam Ngum population; the Sirindhorn population also tended to grow faster before reaching sexual maturity, growing slowly afterwards, than did the Nam Ngum population. Additionally, the maximum size in the Sirindhorn population was observed to be smaller than that of the Nam Ngum population. These observations indicated that higher water temperature resulted in earlier maturation and smaller maximum size in C. aesarnensis. Meanwhile, the smaller maximum size observed in the Sirindhorn population was possibly caused by an evolutionary down-sizing resulting from the overexploitation of this population, because Sirindhorn reservoir is exposed to more intensive fishing pressure.