Induction of Polyploidy in Ictalurid Catfish and Comparative Performance of Diploid and Triploid Channel Catfish and Channel X Blue Catfish Hybrids.

This study provided indications of the feasibility of inducing polyploidy in ictalurids (channel catfish, Ictalurus punctatus, and hybrids with blue catfish, I. furcatus) by temperature or hydrostatic pressure shocks as well as the potential for improvement of growth and processing traits in triploid channel catfish x blue catfish hybrids. One-cell embryos of ictalurid catfish were subjected to either temperature or hydrostatic pressure shocks for induction of triploidy or tetraploidy. Hatch rates of embryos treated for induction of tetraploidy with hydrostatic pressure shocks were lower than those treated for induction of tetraploidy with heat shocks. Hatch rates of embryos tested for induction of tetraploidy with hydrostatic pressure shocks were lower than those treated for induction of tetraploidy with heat shocks. Heat shock parameters previously reported as being effective for tetraploid induction in channel catfish did not induce tetraploidy in the present study. The most effective heat shock and pressure shock treatments gave similar results, inducing approximately 30-70% tetraploidy. Treatments applied near first cell divisions (80 to 83 min post-fertilization) were more effective for producing tetraploidy than those applied earlier (43 to 75 min post-fertilization) in the cell cycle. It was hypothesized that triploid hybrids might have the advantages of heterosis as well as sterility caused by triploidy. No significant differences ($\alpha$ =.05) were detected in growth, feed efficiency, gonadosomatic index or dressout characteristics between diploid and triploid hybrids raised in 1.3 m diameter tanks, with the exception of the significantly higher (P = 0.0321) condition factor (K) of triploid hybrids. No significant difference was found between diploid and triploid pond-grown channel catfish for harvest weight or dressout percentages; however triploids had significantly lower survival and yield, and feed conversion efficiency. Macroscopic examination of several diploid and triploid catfish revealed the expected lack of sexual development and gonadal maturation in channel catfish triploids. The goal of sterility-induced increases in dressout percentage through induced polyploidy remains elusive. None of the significant differences I found between polyploid and diploid ictalurids would lead to economic benefit to the catfish industry. (Abstract shortened with permission of author.)