Biological traits of rare males in the population of Carassius gibelio (Actinopterygii: Cyprinidae) from Lake Pamvotis (north-west Greece)

The gynogenetic population of Prussian carp Carassius gibelio in Lake Pamvotis (north-west Greece) included a small percentage of males (2–3%). Cytogenetic analysis revealed heterogeneity of the population at the ploidy level: all females were triploid (modal chromosome number 156–162 chromosomes) while the males were either triploid (modal number 156–158 chromosomes) or tetraploid (modal number 200–214 chromosomes). Morphometric analysis revealed significant differences in body shape among these three groups. The males were more slender than females, while the triploid males could be discriminated from the tetraploid by the morphology of their caudal peduncle. The males attained a significantly lower asymptotic standard length (LS) (25·04 cm) than females (29·75 cm) and had lower exponent b of the LS and mass relationship. Under laboratory conditions, intraspecific crossings of C. gibelio males with females could give viable all-female offspring; in comparison with goldfish Carassius auratus males, the fertility of the C. gibelio males was generally reduced but remained highly variable among individuals.