EVALUATION OF THREE INDUCING AGENTS FOR ARTIFICIAL PROPAGATION OF LARGEMOUTH BASS Micropterus salmoides

Human Chorionic Gonadotropin (HCG), Ovaprim, and a new spawning agent, GnRH IIa (D-Arg6-Pro9-NHet), were evaluated for artificial propagation of Largemouth Bass. Four year old brood stock were reared on an artificial diet in 0.1 acre ponds, provided forage, and segregated by sex prior to the spawning season. Mean female weight among 54 fish was 1125 ± 34 g and mean male weight among 54 fish was 921 ± 29 g. All fish were given a single intramuscular injection early in the morning and examined for a response the following day. HCG was applied at a rate of 4000 IU/kg for females and 2000 IU for males. Ovaprim and GnRH IIa was applied at a rate of 0.5 ml/kg and 0.1 mg/kg in a single injection to both male and female brood stock, respectively. Each female was assigned an individual net enclosure. Fish that freely expressed eggs in volume were selected for stripping and anesthetized in MS-222. Fish were patted dry and eggs from each female were stripped into a dry bowl, weighed, sampled, and then combined by treatment prior to fertilization.

The respective response rate for HCG, Ovaprim, and GnRH IIa was 83%, 67%, and 50%, with a mean response of 26.6, 23.8, and 17.6 grams of eggs/kg brooder (Table 1). Regardless of spawning agent, it was not possible to strip milt from males to fertilize eggs. Males were euthanized, the testes were extracted, macerated in 0.85% NaCl solution, and the suspension was used for fertilization. Number of fry/jar was estimated volumetrically by taking three samples of a known volume from a total volume of 10 L and counting individual fish in each sample. Mean fry yield/hatching jar was only 5.2% in the HCG treatment, 5.0% in the Ovaprim treatment and 3.4% in the GnRH IIa treatment.