SPAWNING CYCLE AND OOCYTE MATURATION IN LABORATORY-MAINTAINED GIANT FRESH-WATER PRAWNS (MACROBRACHIUM-ROSENBERGII)

Ovarian development of laboratory-maintained female Macrobrachium rosenbergii was classified into four stages, stages 0, 1, 2 and 3, based on external examination of coloration and the relative size of the ovaries to the size of the cephalothorax. Ovaries at each stage consisted of oocytes at various developmental stages. Mature ovaries had a high proportion of mature oocytes. Chromosomes of the oocytes were arrested at diplotene of the first meiotic prophase during vitellogenesis. An increase in the number of oocytes undergoing germinal vesicle breakdown and entering the first meiotic metaphase was found after a premating molt. The oocytes persisted at this stage even after spawning. The intermolt period producing ovarian growth lasted longer than that producing somatic growth. In some females the emphasis in development was on somatic growth after spawning, so that a regular molt followed. On the other hand, development of reproductively active females still emphasized ovarian growth after spawning and a premating molt followed, resulting in a consecutive spawning. Spawning in unmated females commenced much later than that in mated females; and the spawning time was relatively predictable in mated females.