Shellfish Breeding and Hatchery Management (2+1)

17.1.3 Role of eyestalk in the reproduction of crustaceans

In prawns, the neutrosecretory centers located in the ganglia of eyestalk (X organ sinus gland complex), brain and thoracic ganglia mainly influence the egg production (vitellogenesis). While the X organ sinus gland complex of the eyestalk inhibits vitellogenesis under the influence of its hormone, viz., Gonad Inhibiting Hormone (GIH), the brain and thoracic ganglia promote vitellogenesis by their hormone, viz., Gonad Stimulating Hormone (GSH).

Under natural conditions, when the physiological parameters of the prawns and the environmental factors are favorable, the GSH promotes vitellogenesis. On the basis of this principle, the ovarian development and maturation of gonads are obtained in prawns through the unilateral eyestalk ablation (removal of one of the eyestalk). It is also worth mentioning here, that the removal of both the eyestalks though lead to rapid ovarian growth, spawning does not result due to physiological stress. It has been observed that the ova are reabsorbed in the ovary. The eye stalks apart from GIH, produce other neutrosecretory hormones which regulate lipid metabolism and protein synthesis in hepatopancreas; induce hyperglycemia in blood to combat stress; regulate calcium metabolism during cuticle formation; effect water balance during moulting; inhibit production of moulting hormone by ‘Y’ organ and influence movement of pigments in chromatophores.

- Removal of both eyestalk is called as bilateral eye stalk ablation.

- The behavioral pattern of the eye stalk ablated females especially their feeding and matting are also not affected.

Points in eyestalk ablation in crustaceans:

1. For the procurement of broodstock of crustaceans for inducement, some of the shrimps / prawns / crabs are reared in ponds to harvestable size and later they may be allowed to grow for further period of one year before subjecting them for eyestalk ablation.

2. The eyestalk ablation is carried out only in female and not in male.

3. For eyestalk ablation, P. indicus with a carapace length of 30 mm (total length, 150 mm weight > 20 g) and P. monodon with the carapace length of 50-80 mm (total length > 200mm and weight >100g) are normally selected.

4. Before removing eyestalks, the brood stocks are kept in large plastic pools containing filtered sea water of 33 ± 20%.

5. After about 24 hrs, the eyestalks are removed in the females using electrocauterization technique.

6. The ablated female and unablated males are then kept at 2:1 in larger circular plastic lined pools, in which the sea water is made to circulate through sub-gravel filter by air lifts.

7. The breeders are fed ad libitum using chopped fish or calm meat.

8. The temperature, salinity and pH of the medium are maintained at 28 ± 2, 32 ± 2% and 8-8.2 respectively.

Generally the mating and impregnation are ensured in the shrimps if the males and females are kept separately in two tanks and the females are introduced into the male tank when they are about to molt. The separation of sexes seems to enhance the attraction between them and facilities early spawning.