Effect of eyestalk ablation on the rematuration of female macrobrachium rosenbergii (De Man) in captivity

Abstract

The giant freshwater prawn, Macrobrachium rosenbergii is one of the commercially important spccces widely cultured throughout the tropics, subtropics and some parts of the temperate region. Non- availability of brood stock in sufficient numbers at appropriate time has been the greatest constraint for successful operations of prawn hatcheries. To avoid entire dependence on natural sources, development of brood stock of female prawns in captivity is essential. The objectives of the present study were to find out the role of eyestalk ablation on rematuration of spent female of M. rosenbergii in captive conditions and to study the histology of the ovary during rematuration of eyestalk ablated and unablated spent female of M. rosenbergii. In the rematuration experiment the effect of eyestalk ablation on moulting frequency, spawning frequency, larval hatch fecundity, incubation period, ovarian development and ovarian index of spent female of M. rosenbergii was evaluated for 60 days. The histology of ovary in M. rosenbergii during rematuration was also studied. The analysis of the result was done with student's t-test and paired t- test. A significant difference was observed in moulting frequency and spawning frequency of ablated and 'unablated spent female of M. rosenbergii. Larval hatch fecundity of ablated and unablated spent female of M. rosenbergii was not found to vary significantly. Significant difference was found in larval hatch fecundity after first time and second time hatching of both ablated and un ablated individuals. The incubation period was not found to vary significantly among ablated and unablated. However, slight reduction in incubation period was observed in ablated ones. Five histological stages of ovaries viz. previtellogenic stage, early vitellogenic, vitellogenic and late vitellogenic and matured oocytes were observed. In the histological sections of the ovaries, starting from spent ovary to the ripe ovary at weekly interval, similar type of oocyte development stages were observed in both ablated and unablated. IIowever, the size of largest oocyte in ablated was slightly higher than the size of oocyte in unablated at each week of development. It was observed in the present study that ovarian index of ablated spent female was higher than unablated at each week of development. The rematuration experiment has shown that eyestalk ablation significantly enhanced moulting frequency and spawning frequency but the effect was insignificant in terms of larval hatch fecundity and incubation period in spent female of M. rosenbergii. Insignificant increase in ovarian development and ovarian index were also observed in ablated spent female of M. rosenbergii.