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 partial ly 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 homozygou s clones. There was no significant difference in growth rate or FCR be tween individual E4 groups. Within the E20 offspring, both E20 X WT an d E20 X E5 had a significantly higher growth rate than the E20-gyn gro up. All E4-derived groups differed significantly in length and body we ight at 24 weeks post hatching, but there were no significant differen ces in length and body weight between E20-derived groups. The variatio n in length and body weight increased in homozygous clones when compar ed with the other groups, while the E4 X E5 and E20 X E6 fish exhibite d the lowest variation, (5% for length and 15-16% for body weight). Re plicates of the homozygous clones and F1 hybrids, treated with 50 ppm 17alpha-methyltestosterone (MT) to induce sex reversal, showed a signi ficantly 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 variat ion 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.