Hormone induced spermatogenesis and spermiation in barramundi, Lates calcarifer (Bloch)

Between June 1990 and July 1993 a variety of reproductive hormones were tested for their effect on spermiation, spermatogenesis and spawning performance in male barramundi, Lates calcarifer. The study originated from problems experienced with male barramundi spawners during the 1988/89 spawning season. The hormones and dose rates tested in the spermiation experiments were: irradiated carp pituitary extract (iCPE), in 2 intramuscular injections, 24 hours apart, at 8 mg kg\\(^{-1}\\); luteinising hormone releasing hormone analogue (LHRHa, des-Gly\\(^{10}\\)[d-Ala\\(^6\\)]-LH-RH-ethylamide), injected at either 25 or 50 ˜í¬¿g kg\\(^{-1}\\); LHRHa at 25, 50 or 100 ˜í¬¿g kg\\(^{-1}\\) plus pimozide (a dopamine antagonist) at 1.0 mg kg\\(^{-1}\\); Ovaprim SC (A commercial preparation of salmon gonadotrophin releasing hormone analogue and dopamine antagonist) at 0.1 ml kg\\(^{-1}\\); 17˜í¬±, 20˜í‚â§-dihydroxy-4-pregnen-3-one (17˜í¬±-20˜í‚â§P), a progestin steroid at 1.0 mg kg\\(^{-1}\\); and Sustanon '250', a combination of testosterone esters, at 0.5 or 1.0 ml fish\\(^{-1}\\). The results of the spermiation experiments suggest that, LHRHa at 25 ˜í¬¿g kg\\(^{-1}\\), Ovaprim and 17˜í¬±-20˜í‚â§P have the best potential for the development of a hormone therapy for increasing spermiation. Results from the spermiation experiments were tested during actual spawning trials to see if hormone therapy influenced spawning success. It was found that the fish were just as likely to spawn if they had not received hormone treatment. In addition, it was determined that male barramundi do not have to be in running ripe condition prior to addition to the spawning tank. Interaction with the ovulating female appears to be one of the most important factors influencing spawning success. The spermatogenesis experiments examined the effect of chronic hormone therapy over periods longer than one month. In five of the spermatogenesis experiments the fish were implanted with slow releasing cholesterol pellets containing one of the following hormone combinations: 17˜í¬±-methyltestosterone (17-MT), 100, 200 or 400 ˜í¬¿g kg\\(^{-1}\\); LHRHa, 25, 50 or 100 ˜í¬¿g kg\\(^{-1}\\); LHRHa + 17-MT, 25+100, 50+100 or 100+100 ˜í¬¿g kg\\(^{-1}\\). The other experiments examined the implantation of 10 mg of either 17-MT or 19-Norethisterone acetate in silicone pellets and daily, oral administration of 12.5 mg kg\\(^{-1}\\) 17-MT. The experiments were conducted at different times of the year to investigate seasonal response. Of all the hormone treatments tested, only 25 ˜í¬¿g kg\\(^{-1}\\) LHRHa pellets showed any real potential and only during the peak breeding season. Based on these trials it is not possible to develop a protocol, using hormone therapy that reliably enhances the breeding condition of male barramundi. Recent success overseas and in Queensland with environmental control of barramundi breeding provides the best means for control of reproduction.