Evaluation of a Gonadotropin Releasing Hormone Analog of cGnRH II as a Spawning Aid for Channel Catfish Versus Analogs of mGnRH I and sGnRH III

The effectiveness of three different analogs of gonadotropin-releasing hormone (GnRH) to induce spawning in female Channel Catfish Ictalurus punctatus were evaluated concurrently in a blind study. Two of those analogs are currently used under Investigative New Animal Drug by the catfish industry, mGnRH Ia (D-Ala(6), Pro(9)-NHet) and sGnRH IIIa (D-Arg(6), Trp(7), Leu(8), Pro(9)-NHet). A third analog, cGnRH IIa (D-Arg(6), Pro(9)-NHet) derived from a different type of GnRH (i.e., type II), previously thought to have only secondary roles in reproduction compared to type I and III, was also evaluated. The study was divided into four independent, weekly trials over the course of the spawning season, and 78 females were tested for each of the three hormone treatments. Each female received one type of hormone (type I, II, or III) in two doses, one for priming and one for induction: mGnRH Ia or cGnRH IIa at 20 mu g/kg of body weight (priming) and 80 mu g/kg (induction) or sGnRH IIIa at 2 mu g/kg and 8 mu g/kg. Treatment had a significant effect on the mean percent ovulation, cGnRH IIa producing the highest ovulation rate (90.2%), followed by mGnRH Ia (64.9%) and then sGnRH IIIa (44.3%). For females that ovulated, there were no significant treatment differences for number of eggs or viable fry per kilogram of body weight. Therefore, the treatment differences for total egg and fry production reflect hormone effects on ovulation rate while egg quality for females that ovulated was not different among treatments. These results indicate that cGnRH IIa shows great potential as a spawning aid for channel catfish, outperforming mGnRH Ia and sGnRH IIIa.