Effect of Carp Pituitary Extract and Luteinizing Hormone Releasing Analog Hormone on Reproductive Indices and Spawning of 3‐Year‐Old Channel Catfish

Abstract

AbstractThe efficacy of pituitary extract from common carp Cyprinus carpio (CPE) and luteinizing hormone releasing hormone analog (LHRHa) treatments in inducing spawning in channel catfish Ictalurus punctatus undergoing their first oogenesis just before the spawning season was evaluated in four commercial strains of channel catfish. Before the hormones were injected, the average oocyte size (1,624 μm) in May, the typical start of the spawning season, was smaller than that considered normal for mature oocytes (3,000 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 before the priming (0 h) and resolving (20 h) doses and 4 h later (24 h). Oocyte germinal vesicle migration and cathepsin B, D, and L activities were assessed at 0 and 24 h. At 20 h, estradiol levels were significantly higher in CPE‐ and LHRHa‐treated fish. For LHRHa‐treated fish, 20‐h levels of T were also significantly higher in LHRHa‐treated fish at 24 h. Cathepsin B and L activities were also significantly higher at this time. 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 noninjected 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. The LHRHa‐injected fish had a 14% greater incidence of spawning than noninjected fish. Fertilization rates were not significantly different among treatments. Of the treated fish, those that spawned had significantly higher plasma E2 concentrations at 20 h. Thus, LHRHa injection of early‐egg‐stage channel catfish could serve to increase the spawning rates of young adults without resorting to intensive spawning techniques.