GENETIC-RELATIONSHIP OF GROWTH, SEX AND GLUCOSEPHOSPHATE ISOMERASE-B PHENOTYPES IN CHANNEL CATFISH (ICTALURUS-PUNCTATUS)

Growth of fish has been associated with the phenotypes of specific bio chemical genetic loci, although the correlation of growth with sex-spe cific loci has not been routinely studied, In a previous study in chan nel catfish (Ictalurus punctatus), glucose phosphate isomerase-B (GPI- B) was linked with the sex-determining gene (SDG) with a recombination frequency of 15.2%. Growth performance related to sex and GPI-B pheno types was investigated in five experimental matings of channel catfish , The association of sex and GPI-B with growth, differences in growth among GPI-B phenotypes, and the degree of linkage with growth between sex and GPI-B were evaluated by ANOVA followed by Duncan's Multiple Ra nge Test (P < 0.05). Significant growth differences were found between males and females in all families examined; males outweighed females by 36%, confirming observations from earlier studies. The phenotypes o f GPI-B were also associated with growth; however, heterozygotes at GP I-B exhibited higher relative weight than homozygotes only when the pa ternal parent was heterozygous, indicating that the heterozygosity of this allozyme did not directly induce the observed growth advantage. N o growth advantage of heterozygosity in GPI-B was observed when recomb ination occurred between GPI-B and SDG; male and female recombinants h ad similar or lower relative weights compared to offspring with parent al genotypes. These data indicate that sex is more tightly linked with growth-related gene(s) than GPI-B phenotypes, and no evidence support ed direct involvement of GPI-B in growth of channel catfish.