海岸地帯管理ジャーナル

概要

Embryonic Development of Macrobrachium idae (Heller, 1862)

Sudhakar S, Soundarapandian P, Varadharajan D and Dinakaran GK

The egg laying usually takes place between 6 and 20 hrs after mating. The laying of one whole batch of eggs is usually completed within 20 mins. The eggs are extruded through the female genital pores into the brood chamber, first on one side then the other. The chamber between the 4th pair of pleopods is filled first, then those between the 3rd, 2nd and 1st pairs, successively. The eggs are held in bundles like grapes by an extremely thin elastic membrane which is believed to be secreted by the ovigerous setae. During the development in prawns the colour of the eggs changed through greenish opaque, light green, brownish-yellow and dull whitish in colour. The embryonic stages are very much useful in recognizing the stages of development of the species. The process of embryonic development includes nuclear division, cleavage (blastomeres), segmentation, formation of optic vesicle, eye pigment development and larva formation. At third minute after mating the sperm fused with the egg membrane and subsequently the male pronucleus entered the egg’s cytoplasm. The first and second nuclear divisions were completed without any corresponding division of the cell. Third division begun at 8 h and eight nuclei were formed after 9 hrs. Subsequent divisions of sixteen and thirty two nuclei stage took place at about 1 to 1.30 hrs interval and segmentation was completed at 22-24 hrs. Embryonic development follows the normal blastula and gastrula stages, ending with the closing of the blastopore. When larva hatches out from the eggs, they undergo a series of development stages before metamorphosing to juvenile. During this period, they exhibit marked variations in morphological features. These variations are unique for each and every species according to the developmental stages.