Approaches to Improve Production and Performance of Channel Catfish (Ictalurus punctatus) Female x Blue Catfish (I. furcatus) Male Hybrid Catfish

Abstract

Xenogenesis was studied as a method for the production of hybrid catfish fry via mating xenogeneic males with normal channel catfish Ictalurus punctatus females. Spermatogonial type A cells were isolated from blue catfish I. furcatus. Cells were transplanted into confirmed triploid channel catfish. The live cells were introduced to the gonads of the host via catheterization or by surgery followed by injection. A mean of 5.23x105 cells (2x104 – 1.43x106) were introduced by catheterization and mean of 7.25x105 cells (5x104- 1.8x106) cells injected via surgical injection. DNA was analyzed from biopsies of the gonads and 80% of the fish were xenogenic, having blue catfish cells in their gonads. Ten months after implantation, a sample of 8 males were tested and 7 were xenogenic. The xenogenic males successfully courted normal channel catfish that had been hormone induced, but none of the eggs hatched, indicating inadequate sperm production or an inability to ejaculate. However, some males testes were well-developed morphologically, and large scale sperm production was detected in 3 of 7 xenogenic males examined two years after transplantation and after hormone therapy with luteinizing hormone releasing hormone analogue. Sperm was removed from a male that had been surgically transplanted with blue catfish cells, and used to fertilize eggs from a hand-stripped channel catfish female. One percent of these eggs hatched. All seven surviving 6-month-old progeny of this male had the external morphology, swim bladder shape, nuclear DNA profile and mitochondrial DNA profile of F1 channel catfish female X blue catfish male hybrids. This indicates that the sire was indeed a xenogenic channel catfish producing only sperm from blue catfish and these progeny were produced through xenogenesis. This is the first report of successful production of xenogenic catfish, and the first report of producing 100% hybrid progeny through xenogenesis in fish.

The second study investigated genotype- environment (GE) interactions of eight genetic types of channel catfish female x blue catfish male catfish hybrids. These hybrids were reared in four different environments; a low density pond, high density pond, split pond and in-pond raceway. Feed conversion ratio (FCR) by environment was better than what is usually expected for research and on farm for ictalurid catfish.

The FCR was 1.28, 1.99, 1.65 and 1.52 for the low density pond, high density pond, split pond and in-pond raceway, respectively. Genetic type, sex, environment and all possible interactions affected body weight for the different genetic types of channel catfish female x blue catfish male hybrids (P <0.05). MS X RG and KS X RG were the largest two genetic types in each environment, indicating that a single genetic enhancement program could address the improvement of hybrid performance for all culture systems used in the catfish industry. Hybrids produced by MS and KS females selected for increased body weight for 8 generations were larger compared to hybrids from MR and KR random controls in all environments. GE interactions were observed in regards to the sex, and differences were found (P<0.05) between males and females for final body weight. Survival in high density pond, split pond and in-pond raceway from stocker stage to the harvest in the current experiment was as high as 96%. Harvestability was impacted by environment (P < 0.05). Fish from the high density pond and the in-pond raceway, respectively, were the easiest to capture.