Studies for Improvement of Reproductive Biotechnology for Production of Channel Catfish (Ictalurus punctatus) Female X Blue Catfish (Ictalurus furcatus) Male Hybrid Embryos

Abstract

Investigative studies were conducted on the relative effectiveness between carp pituitary extract (CPE), luteinizing hormone releasing hormone analog (LHRHa) injections and LHRHa implants for producing hybrid catfish embryos. Data from the past 15 years, which included, 25 on CPE, 20 on LHRHa injections, and 20 for LHRHa implants, respectively, were evaluated. LHRHa administered as an injection or implant produced more (P<0.001) fry/kg than CPE. Mean fry/kg female body weight (all females) produced was 948 for, CPE 2,483 LHRHa injections and 2,765 for LHRHa. There was not a significant difference in fry/kg between the two LHRHa treatments. The coefficient of variance indicated more consistent results for CPE (CV=37.5), and LHRHa implants (CV= 35.9) than LHRHA injections (CV= 49.9). The second study investigated the effectiveness of OVA-EAZE a Luteinizing Hormone Releasing Hormone analog (LHRHa). This study investigated des-Gly10,[D-Ala6] LHRH Ethyl amide (LHRHa) administered in two doses of 20 µg per kilogram of female channel catfish body weight as a priming dose, followed 12 hours later by a resolving injection of 100 µg per kilogram of body weight, to determine its effectiveness in inducing ovulation in channel catfish (Ictalurus punctatus). A double blind study was conducted at two sites concurrently with 50 treatment, and 25 control fish at each site using similar protocols. All eggs were fertilized using blue catfish (Ictalurus furcatus) sperm in order to produce hybrid fry. At both sites treated females had a higher ovulation rate (92%, P<0.001), and (84%, P<0.001), compared to sham injected controls (4%) and (4.2%). When secondary variables such as; eggs/kg, egg quality score, latency, hatch percentage, and fry/kg were also evaluated at both locations for the treated fish, it showed the secondary variables for females ovulated at both locations easily exceeded minimum industry standards for channel catfish females. At Baxter Land Company (AR), eggs/kg, egg quality score, latency, hatch percentage, and fry/kg were 8,665, 3.5, 44.4 hours, 31.3% and 2,401, while at Auburn University, eggs/kg, egg quality score, latency, hatch percentage and fry/kg were 10,385, 3.8, 46.2, 41.3% and 3,700 for females injected with LHRHa. The third study focused on the toxicity and target animal safety of OVA-EAZE, luteinizing hormone releasing hormone analogue (LHRHa). The experimental animals (channel catfish females) were administered 0, 180, 540 and 900-µg/kg female body weight of LHRHa and observed for seven days. Seven-day survival, as well as the histopathology of the spleen, ovary, liver, kidney, gill, muscle, heart, stomach and intestine of fish was assessed to determine the possible toxic effects of LHRHa. The seven-day survival was 62.5, 87.5, 75.0 and 75.0% between the four treatments and was not significantly different (P = 0.05). Of those fish that died, the time to death was not different among treatments. The mean severity of the mouth kidney and eye abnormalities was higher (P = 0.05) for the sham-injected controls. The observed liver discoloration tended to increase with dosage, however, there were no significant (P=0.05) differences among treatments. No consistent or significant (P = 0.05) trends in histopathological abnormalities existed among treatments. Observed intestinal inflammation appeared to be more prevalent with increasing dosage. Bacterial and parasitic load also appeared random and there were no significant differences. The final study focuses on xenogenics as a novel method for the production of hybrid catfish fry. Putative spermatogonia A, and primordial germ cells from a fresh cell isolate or a density gradient-centrifuged isolate from blue catfish, testes were inserted into the, gonads of confirmed triploid channel catfish. The live cells were introduced to the gonads of the host via catheterization or by surgically accessing the gonads and inserting the cells directly into the ovaries or testes with an injection of (mean: 5.23x105) cells. Sixty days post introduction of the cells into the host, DNA was analyzed from biopsies of the gonads. Two triploid channel catfish, inoculated with density gradient sorted blue catfish stem cells introduced by injection contained viable blue catfish cells in their ovaries and testes 60 days later. Three triploid channel catfish that were inoculated with testicular cells from blue catfish introduced by catheterization via the genital and urogenital opening respectively, contained viable blue catfish cells in their ovaries and testes 60 days later. This is the first report of successful production of xenogenic catfish in the United States.