GONADOTROPIN RELEASING HORMONE ANALOGUE STIMULATED SPERMATOPHORES MATURATION OF HATCHERY-DISCARDED MALE TIGER SHRIMP, Penaeus monodon WITHOUT EYE STALK ABLATION  

The use of broodstock in hatchery for nauplii production is basically only for short periode. When the production target is achieved, normally both female and male stocks are discarded. A series of trial was conducted on male tiger shrimp which were discarded from hacthery in order to evaluate the effect of injection of salmon gonadotrophin releasing hormone analogue (sGRH-a) on spermatophores maturation against eye stalk  ablation.

This study consisted of two trials; the first one was arranged with three treatments, injection of sGRH-a at two dosages of 0.1 (OV1) and 0.2 (OV2) mL/kg shrimp and eyed ablation (AB) as the control. Following trial comprised of two treatments in which the dosage tested was the optimal dose obtained in the first trial (0.2 mL/kg shrimp) and control ablation (AB).  Discarded male stocks were randomly distributed with density of 14 males for the first trial and 12 males for the second trial. Injetion was carried-out three times with interval one week for the both trials.  A week after the last injection, males were electrically shocked to release their spermatophores.

At the first trial, number of male releasing spermatophores at maturation and first rematuration was higher in shrimp induced with OV2 followed by OV1 and  AB (Table 1). Number of male releasing spermatophore in the second trial  was also higher in shrimp induced with 0V (58.3%) compared to AB which was 50% (Table 2). However, number of male releasing spermatophore at rematuration 1 and 2 was higher at AB  than OV.  Weight of spermatophore seemed not affected by the treatments but more related   to  the  weight  of the  male  used which in trial 1 were bigger than in trial 2. There was no clear trend of the cell number of  sperm in spermatophore related to the treatments, however, ablated shrimp produced higher sperm cell (101.2 x 10⁶ cell/shrimp) than OV (89.5 x 10⁶ cell/shrimp) only at the first maturation. In general, the sperm cell number   showed a decrease by increase the spawning frequency for both treatments.