Gynogenesis in common carp (Cyprinus carpio L.). III. The effects of inbreeding on gonadal development of heterozygous and homozygous gynogenetic offspring

The gonad development and fertility were compared for three offspring groups produced by full-sib mating (FS group: F = 0.25), gynogenesis by retention of the second polar body (2PB group; F unknown) and gynogenesis by endomitosis (EM group: F = 1), using the same common carp female. 2PB offspring were all female, but the homozygous EM offspring consisted of 50% males and intersexes which were homozygous for a recessive mutant sex-determining gene. Another mutant, affecting pigmentation in eggs, was likewise detected in the EM offspring but not in the 2PB offspring. The variation in body weight, gonad weight and egg size in each group increased with increasing degree of inbreeding. FS and 2PB offspring were comparable in mean gonadal development, but gonads from homozygous gynogenetic carp were often retarded. The ovulation response significantly decreased with increasing levels of inbreeding. Yields of normal fry were reduced in crosses involving milt from FS males and eggs from FS and 2PB females as compared with crosses with eggs or milt from EM animals. FS eggs fertilized with EM milt gave significantly better yields of normal fry than any other group. Taken together these results suggest that 2PB gynogenetic offspring are largely heterozygous for many deleterious genes affecting reproduction. In contrast, homozygous EM offspring display considerable inbreeding depression in gonad development but recessive lethal genes are excluded from the genepool.