GYNOGENESIS IN COMMON CARP (CYPRINUS-CARPIO) .4. GROWTH, PHENOTYPIC VARIATION AND GONAD DIFFERENTIATION IN NORMAL AND METHYLTESTOSTERONE-TREATED HOMOZYGOUS CLONES AND F(1) HYBRIDS

Growth rate and phenotypic variation in length and body weight of two homozygous gynogenetic clones E4-gyn and E20-gyn, and four F1 hybrids E4 X E5, E4 X E6, E20 X E5 and E20 X E6, was compared with two partially outbred groups E4 X WT and E20 X WT. There was a significant effect of sire on growth rate and food conversion ratio (FCR) in both the E4 and E20 groups, caused by differences between WT groups and homozygous clones. There was no significant difference in growth rate or FCR between individual E4 groups. Within the E20 offspring, both E20 X WT and E20 X E5 had a significantly higher growth rate than the E20-gyn group. All E4-derived groups differed significantly in length and body weight at 24 weeks post hatching, but there were no significant differences in length and body weight between E20-derived groups. The variation in length and body weight increased in homozygous clones when compared with the other groups, while the E4 X E5 and E20 X E6 fish exhibited the lowest variation, (5% for length and 15-16% for body weight). Replicates of the homozygous clones and F1 hybrids, treated with 50 ppm 17alpha-methyltestosterone (MT) to induce sex reversal, showed a significantly depressed growth rate and FCR when compared to the untreated groups. Mean length and body weight were also significantly depressed in all E4-derived groups but not the E20 groups. The phenotypic variation increased in all groups except E20 X E6. Sex reversal was in most cases incomplete. The percentage of sex-reversed males varied from 17 to 23% in the homozygous clones and from 3% to 28% in the F1 hybrids. Only the E20 X E5 group contained 69% males.