Observations on complete and partial, spawning and related seed production in Penaeus semisulcatus

Abstract

Complete and partial spawnings in Penaeus semisulcatus are reported,. Among the 106 specimens ranging in size from 131 to 210 mm in total length utilized for spawning, higher percentage of full spawning was observed in prawns belonging to the size group 131-150 mm. Among the partial spawnings highest percentage was recorded in 151 - 170 mm size group. In the larval rearing experiments, the average survival rate of larvae, between those observed in the fully spawned and partially spawned groups, was better in the former group. While there was no significant difference in the larval survival rate obtained between the fully and partially spawned prawns in the size of 131 - 170 mm, considerable difference was observed in higher size groups of 191 - 210 mm. Besides the causes such as stress, crowding, adverse environmental conditions, disturbance during spawning process, overripe and not fully matured conditions of the ovaries, are suspected to be the other reasons for bring forth partial spawning. The result of spawning performance and larval survival shows that P. semisulcatus measuring 151 - 170 mm are more suitable for spawning and seed production than the larger size groups.