Survival and Development of Larvae and Juveniles of the Mud Crab [Scylla olivacea Forskal (Crustacea: Decapoda: Portunidae)] at Various Temperatures and Salinities

An experiment was carried out to determine temperature and salinity effects on the survival and development of each stage of the larvae and juveniles of the mud crab (Scylla olivacea Forskal). Salinities of 15, 25, 35 and 45 9 L(-1) were tested for zoea; 5, 15, 25, 35 and 45 g L(-1) for megalopae and 0, 5, 15, 25, 35 and 45 g L(-1) for crab instar (C1) juveniles, at temperatures of 20, 26 and 32 degrees C. The survival of zoea and megalopae was affected by the separate effects of salinity and temperature and by their interaction. The survival of Cl juveniles, on the other hand, was influenced by the separate effects of salinity and temperature but not by their interaction. Z1-Z3 larvae survived at salt concentrations of 25-35 g L(-1) at 20, 26 and 32 degrees C but survival at 15 and 45 g L(-1) occurred only at 32 degrees C. Z4-Z5 larvae survived at 15-35 g L(-1) at all temperatures, but survival was low at 15 g L(-1) at 20 degrees C. At 45 g L(-1), none of the Z5 larvae reached megalopa. The megalopae developed to juveniles at 25-35 g L(-1) at 20 degrees C; at 15-35 g L(-1) at 26 degrees C; and at 15-45 g L(-1) at 32 degrees C. At C1 juvenile stage, there was high survival at 5-35 g L(-1) at all temperatures (20, 26 and 32 degrees C). In salinity-temperature combinations where the larvae survived, onset of development was delayed for 5-10 d on Z3 larvae reared at 25-35 g L(-1) at 20 degrees C and in Z5 larvae reared at 15 g L(-1) at 20 degrees C. Duration of development was not significantly different at all stages, except in megalopa where it was delayed at 35 g L(-1) at 20 degrees C. On the other hand, development of C1 juveniles was synchronous at 5-35 g L(-1) at 20 degrees C and at 5-45 g L(-1) at 26 and 32 degrees C. Gradual transfer to 15 g L(-1) from 31-32 g L(-1) did not provide additional benefit to zoea while slow transfer to 45 g L(-1) from 31-32 g L(-1) improved survival of megalopae. Generally, there was increased tolerance to low salinity and low temperature as the larvae grew to juveniles.