Shellfish Breeding and Hatchery Management (2+1)

3.1.9 Mating characteristics in open vs closed thelycum species

3.1.9 Mating characteristics in open vs closed species

Penaeus species are grouped into two broad categories based on differences in morphology of the female genital organ or thelycum which occupies the area from the third to the fifth periopods. The “open thelycum” species include the members of the Litopenaeus subgenera. They receive spermatophore or sperm packet from the male and retain it externally for a few hours perior to spawning.

In contrast, the “closed thelycum” species are those which mate each time the female molts. The closed thelycum female receives the spermatophore into her thelycum and then her new exoskeleton gets hardened over it. She retains the spermatophore until she utilizes the sperm in one or several spawning. The subgenera Penaeus, Fenneropenaues, Marsupenaeus and Melicrotus have the closed or internal type thelycum.

This open thelycum females follow a sequence of molt-mature- mate and spawn while closed thelycum species follow a sequence of molt- mate-mature and spawn. In both groups, males with hard exoskeleton deposit spermatophores into females. Multiple spawns may occur within one intermolt period for both open and closed thelycum speices.

The stimulus for courtship behaviour in Penaeus sp. is believed to be motivated by the sex pheromone secreted in the females and received by the males through their antennules or antennular flagella. In open thelycum species, mating occurs mainly in the evening and in the night spawning will occur.