Growth and Reproductive Biology of the Freshwater Shrimp Exopalaemon Modestus (Decapoda: Palaemonidae) in a Lake of Korea

Abstract

The growth and reproductive biology of the freshwater shrimp Exopalaemon modestus were studied in Young-am Lake, Korea, from January to December 1999. Female maturity was determined by the size of ovigerous females and of females with maturing ovary. The size at which 50% of females are mature is estimated as |$11.55 \pm 1.95 \ {\rm mm}$| carapace length. Brood size was isometric functions of female body size. Based on dry weight, the reproductive output (mass of incubating eggs/mass of female) averaged 0.17. Ovigerous females occurred in May–September. Higher gonad index was observed from May–June (percentage ovigerous |$>50\%$|⁠). Significant difference in ovarian weight between females with noneyed eggs and eyed-egg stage was found. This indicates that ovarian maturation occurs during the incubation time, suggesting that females were potentially consecutive breeders, capable of multiple spawning during a reproductive season. Spawning by a single female seems to occur consecutively in a single reproductive period. The length-frequency distribution showed that the population had two modal size groups per year, displaying similar pattern in both males and females. Parameters of growth were estimated using the von Bertalanffy growth function (VBGF). Females grew faster and reached a larger size at age than males (⁠|${\rm K} = 0.58 \ {\rm yr}^{-1}$| and |${\rm L}_{\infty} = 21.39 \ {\rm mm}$| CL for females, and |${\rm K} = 0.62 \ {\rm yr}^{-1}$| and |${\rm L}_{\infty} = 18.40 \ {\rm mm}$| CL for males). Longevity was estimated to be 1.1–1.3 yr.