Observations of poor hatching in the unilateral eyestalk-ablated females of Penaeus monodon Fabricius

The eyestalks of 16 wild females of Penaeus monodon were ablated in August and the eggs spawned by 7 females were hatched. In the other 9 females, the spermatophore was not detected in 3 females and the thelycum abandoned in 6 females. Eyestalk ablation was performed on 20 pond-reared adult females in December. Only 5 females spawned, but their eggs were not hatched. In pond-reared adult females, only 5% females were copulated, though 40% of the wild females contained spermatophores in the seminal receptacles. The possible causes of low hatching rate in ablated females are absence of spermatophore in the seminal receptacle, insufficient quantity of spermatozoa remaining in the seminal receptacle and loss of thelycum during ecdysis.