Effects of Temperature on the Survival, Spawning and Egg Incubation Period of Overwintering Mud Crab Broodstock, Scylla paramamosain (Brachyura: Portunidae)

Abstract

This study was conducted to examine the effects of temperature on the survival and spawning of overwintering broodstock females of the mud crab, Scylla paramamosain in a hatchery. The relationship between the mean water temperature (T) and the number of days required for egg incubation (D) was also analyzed using the following three equation models: power function, D=aT^b; Belehrádek's equation, D=a (T-α) ^b; and an equation based on the theory of heat summation, D=a/T-α, to predict the hatching date of larvae for use in mass seed production. The survival rates of the overwintering females tended to be improved in the groups held at controlled temperatures (range of mean temp., 14.9-17.7°C) compared to those reared in the tanks in which the temperature was allowed to fluctuate naturally (range of minimum temp., 8.6-8.8°C) . Winter spawning was induced under the high temperature regime. The Belehrádek's equation had the best optimality to the relationship between the temperature and the egg incubation period. The biological lower critical temperature represented by the parameter α was estimated as 12.19 and 13.98°C in the Belehrádek's equation and the heat summation theory, respectively. However, the females held under 18°C hatched non-viable larvae (=prezoeas) . Consequently, the actual lower critical temperature for egg development and hatching is concluded to be more than 18°C.