Evaluation of Hormonal Agents for Artificial Propagation of Largemouth Bass

Abstract

A synthetic gonadotropin‐releasing hormone, cGnRH IIa (D‐Arg6, Pro9‐NHet), was evaluated versus commercially available hormones as a spawning aid for Largemouth Bass Micropterus salmoides with two trials each season for two seasons. In season one, human chorionic gonadotropin (HCG) was applied at a rate of 4,000 IU/kg for females and 2,000 IU/kg for males. Ovaprim (Western Chemical, Ferndale, Washington) and cGnRH IIa was applied at 0.5 mL/kg and 0.1 mg/kg in a single injection. The respective response rate for HCG, Ovaprim, and cGnRH IIa among females was 88.9, 77.8, and 50%. Mean latent period for HCG, Ovaprim, and cGnRH IIa among females was 33.4, 34.4, and 34.7 h. In season two, four treatments were used: saline, HCG, cGnRH IIa, and cGnRH IIa with the dopamine inhibitor domperidone (cGnRH IIa+D). Males did not express milt in either season, so they were euthanized to collect testes and prepare a fertilization solution. Spawns were segregated by spawning agent and incubated in hatching jars. Response rates of females to saline, HCG, cGnRH IIa, and cGnRH IIa+D were 0, 75, 90, and 75%, respectively. There was no statistically significant difference among the treatments for response, eggs per kg of female body weight, number of eggs/g, or latent period. Hatched larvae yield from hatching jars ranged from 0.5% to 19.5%. The spawning agent cGnRH IIa had similar efficacy as commercially available HCG. This investigation also examined the efficacy of a fertilization solution generated following extraction and maceration of testes. Testes of mean weight 6.6 g yielded spermatozoa at a mean density of 6.0 × 109 spermatozoa/mL. There was no significant effect of inducing agent on sperm density of solution. Spermatozoa were characterized in three groups regarding motility: nonmotile, progressively motile (desired), and non‐progressively motile. Sperm motility videos revealed a mean progressive motility of 7.9%. Mean values for nonmotile and non‐progressively motile spermatozoa were 75.5% and 16.6%, respectively. Mean duration of motility was 116 s.