Lecture notes on reproduction, fertilization and development in penaeus (prawn)

Penaeus Female Reproductive System:

The female has a pair of long ovaries extending the whole length of the thorax and the abdomen along the median line. The two ovaries are fused together posteriorly, but free anteriorly. Near the anterior end the ovaries produce finger-like outgrowths called diverticula. From each ovary arises an oviduct.The oviduct opens to the third walking leg.

Penaeus_Male Reproductive System:The male has a pair of tubular testes located in the thorax on either side of the middle line. The two testes are fused together anteriorly.Each testis has many finger-like outgrowts called diverticula. Posteriorly, the testis leads into a vas deferens. The terminal end of the vas deferens becomes dilated into an ejaculatory bulb. The ejaculatory bulb opensbto the outside by the male genital pore at thevbase of the last walking leg.

Fertilization and Development:In penaeus  fertilization is external. During copulation, a male puts the female down on her back and deposits sperms (spermatophores) on the ventral surface   in the thelycumnear  the female genital pores. As the eggs come out of female genital pore, they are fertilized by the sperms already present there. The female lays eggs in large numbers. The fertilized eggs are attached to the pleopods by a sticky secretion of the tegumental glands. In Penaeus development is indirect. The fertilized egg hatches into a larva called nauplius. The nauplius is followed by a series of larval forms, namely metanauplius, protozoea, zoea and mysis. Finally the Mysis larva is transformed into a prawn.

1. NaupliusThe larva hatched from the egg is called nauplius larva. It has the following features:It is a free swimming minute, microscopic and pelagic larva. It is oval in shape; the anterior end is broad and the posterior end is narrow.The body has three regions, namely the anterior head, the middle trunk and the posterior anal region.The head has a simple median eye on the dorsal side called nauplius eye.It has 3 pairs of appendages. They develop into the first 3 pairs of appendages of adult prawn. The first pair of appendages is uniramous and is called antennule. The second and third pairs of appendages are biramous and are called antenna and mandible. The mandible has no teeth.The posterior end has a caudal fork.The nauplius larva grows and undergos several moults and finally develops into the next larva called metanauplius.

1. 2. 3. The three pairs of appendages of the nauplius larva (the future first and second antennae and mandibles).

3. Mandible

2. Metanauplius:It is the second larva of Penaeus. It has an anterior cephalothorax and a posterior abdomen. The abdomen ends in a caudal fork.The anterior end has a pair of frontal sense organs. The larva has three pairs of appendages, the next three pairs of appendages develop as buds.

3.Protozoea: Protozoea has an elongated body, divisible into cephalo-thorax and abdomen. Cephalo-thoracic region is covered by a dorsal shield or carapace. Theseven pairs of appendages of metanauplius become well developed. Alittle later, the 3rd pair of maxillipedes also develop. On the sides of the median eye a pair of lateral eyes appear.Protozoea grows in size, undergoes moulting and transforms to zoea.

4.Zoea:Zoea develops from the metanauplius.It is a free swimming pelagic, minute and microscopic.The body is divisible into an anterior cephalothorax and a posterior abdomen.The cephalothorax is covered by a carapace.Anteriorly the carapace is produced into median spine called rostrum.It has a pair of stalked compound eyes.All the 5 cephalic appendages are well developed.In the thorax, the 3 pairs of maxillipedesare slightly developed and the remaining 5 pairs of walking legs are in the form of buds.The abdomen has 6 segments. The last segment ends in a forked telson. The abdomen is without appendages.

5. Mysis:The mysis larva develops from zoea larva.It is elongated, laterally compressed and transparent.The body is divisible into a cephalothorax and an abdomen.The cephalothorax is covered by a carapace.Anteriorly the carapace is produced into a spine called rostrum.All the appendages are developed. They include 5 pairs of cephalic appendages, 8 pairs of thoracic appendages and 6 pairs of abdominal appendages.The thoracic legs are used for swimming. The abdomen ends in a telson.The eyes are stalked and compound.The mysis larva looks like the adult Mysis and hence the name. The larval mysis differs from the adult Mysis in the absence of a brood pouch beneath the thorax and a pair of statocysts.