| Summary: | Growth of fish has been associated with the phenotypes of specific biochemical genetic loci, although the correlation of growth with sex-specific loci has not been routinely studied. In a previous study in channel 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 phenotypes 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 Range 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 of GPI-B were also associated with growth; however, heterozygotes at GPI-B exhibited higher relative weight than homozygotes only when the paternal parent was heterozygous, indicating that the heterozygosity of this allozyme did not directly induce the observed growth advantage. No growth advantage of heterozygosity in GPI-B was observed when recombination occurred between GPI-B and SDG; male and female recombinants had similar or lower relative weights compared to offspring with parental genotypes. These data indicate that sex is more tightly linked with growth-related gene(s) than GPI-B phenotypes, and no evidence supported direct involvement of GPI-B in growth of channel catfish. © 1995.
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