VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

Reproduction in Wild Marine shrimps

REPRODUCTION IN WILD MARINE SHRIMP

• Generally, the male marine shrimps are smaller than females. The female has a characteristic thelycum (sperm storing organ) which is located on the ventral side of the cephalothorax between the 4^th and 5^th walking legs. The thelycum is of closed type in  Fenneropenaeus indicus and P. monodon. The ovary is found on the dorsal side of the animal along its entire length. In the fully ripe female, the ovary is dark-olive green in colour and has a lateral expansion in the first abdominal segment. The male sexual organ is the petasma which is the modified structure of the first pair of swimming legs attached to the ventral side of the first abdominal segment. The two sperm ducts from the male testis open at the base of the fifth pair of walking legs. The terminal portion of the sperm duct is enlarged to form the terminal ampoule, in which the spermatophore or the sperm pocket is stored. The spermatophore containing the non-motile sperms is visible as a white mass at the base of the fifth pair of walking legs in mature males.

Marine shrimp

Source : Sea ex.com

• The mating takes place between a newly-moulted soft female with immature ovary and a mature male in the intermoult phase and the spermatophore is tucked safely inside the seminal vesicle of the female’s thelycum with the help of the petasma. The emptied spermatophore is retained in the thelycum during the intermoult period or until the female marine shrimp moults and then it is discarded alongwith the moulted cuticle at the time of moulting. It is also found that the sperms which are stored in thelycum for some time acquire the capacity to fertilize eggs. Hence direct mixing of sperms of male and eggs stripped from female does not lead to fertilization of eggs. The technique of removing spermatophore from male by electrojaculation and transferring the sperm pocket to thelycum of a newly moulted female developed recently has been found to be very useful in inseminating P. monodon artificially. Such marine shrimp have been found to mature and spawn viable eggs in laboratory. During spawning, the female releases simultaneously eggs from oviduct and sperm from spermatophore and fertilization takes place in the sea. The fertilized eggs sink to the bottom and come up when the water is agitated.