EVALUATION OF cGnRH IIa FOR INDUCED SPAWNING OF Epalzeorhynchos bicolor AND Synodontis nigriventris

Reproductive dysfunction is a common impediment to the commercial production of many ornamental fish species. Use of exogenous hormone preparations may help to overcome failure of final oocyte maturation and induce ovulation.  Ovaprim® (sGnRHa), is currently the preferred spawning aid used by the ornamental fish industry, however, spawning success using this GnRH subtype may be variable across taxa. An alternative gonadotropin releasing hormone analogue, cGnRH IIa, has been recently shown to exhibit increased biological activity and reliability for induction spawning protocols. This study evaluated the efficacy of two spawning aids, Ovaprim® and cGnRH IIa,on a number of quantitative and qualitative measures of spawning performance in Epalzeorhynchos bicolor and Synodontis nigriventris, two commercially valuable ornamental fish species.

Female broodstock that exhibited >50% germinal vesicle migration from collected biopsies were used in the study. Three cGnRH IIa doses of 50, 100, 200 µg/kg, a single Ovaprim® dose of 10 µg/kg and a propylene glycol control were evaluated. All treatment groups were also administered an equal concentration of a dopamine antagonist (5 mg/kg domperidone). Spawning aids were administered intramuscularly via injection near the base of the dorsal fin. Injection regimes differed between the two species tested but mirrored accepted commercial production protocols. At predetermined time periods, light pressure was applied to the coelom to detect successful ovulation. Females were then stripped and the eggs weighed and fertilized. Embryos were stocked into 1L hatching containers from which a subsample was drawn 1.5 - 2 hours later and photographed to determine fertilization success. Hatching success was determined from an additional 50 embryo subsample stocked into 150 mL screen bottomed specimen cups.

Results of contingency tables indicated no significant differences in ovulation success for either E. bicolor or S.nigriventris (P = 0.499 and 0.071). Total fecundity standardized as eggs per gram body weight (P > 0.159), fertilization and hatching success (P > 0.314 and P > 0.296) were also not significantly different among the four spawning aid treatments in either species. Results from this study indicate that cGnRH IIa performs equivalently to the industry standard Ovaprim® for induced spawning of both E. bicolor and S. nigriventris.