"Effect of Carp Pituitary Extract and LHRH on Reproductive Indices and Spawning of 3 year-old Channel Catfish"

Abstract

The efficacy of carp pituitary extract (CPE) and luteinizing hormone releasing hormone (LHRHa) treatments to induce spawning in young-adult channel catfish undergoing first oogenesis just prior to the spawning season was evaluated in four commercial strains of channel catfish. Prior to injection of the hormones, oocyte development was monitored and average oocyte size in May (1624 μm), the typical start of spawning season, was smaller than that considered normal for mature oocytes (3000 μm) in this species. Priming and resolving doses of CPE, LHRHa, or saline were administered in early May. Plasma estradiol (E2) and testosterone (T) levels were measured prior to the priming (0-hour) and resolving (20-hours) doses and 4 hours later (24-hours). Oocyte germinal vesicle migration and cathepsin B, D, and L activities were assessed at 0- and 24-hours. At 20 hours, estradiol levels were significantly higher in CPE and LHRHa treated fish. For LHRHa treated fish, twenty-hour levels of T were also significantly higher. At 24-hours, cathepsin B and L activities were significantly higher in the ovaries of both CPE and LHRHa treated fish. No differences were observed among the strains evaluated for any of the measured parameters. As oocytes did not yet appear to have entered the final stage of maturation, the fish were returned to ponds with non-injected cohorts to evaluate spawning success. None of the fish injected with saline spawned. On average, 12.5% and 18.8% of those injected with CPE and LHRHa, respectively, spawned. Compared to non-injected fish, the LHRHa-injected fish had a 14% greater incidence of spawning. Fertilization rates were not significantly different among treatments. Of the treated fish, those that spawned had significantly higher plasma E2 concentrations at 20-hours. LHRHa injection of early-egg-stage channel catfish could serve to increase spawning rates of young-adult catfish without resorting to intensive strip-spawning.