The length-weight relationships of the cyprinid fish Carassius gibelio (Bloch, 1782) are described for the 12 most important lakes of Greece. Carassius gibelio is an allogynogenetic fish species, which was introduced into Greek lakes during the late 1970s. The values of the exponent b of the length-weight relationships ranged from 2.33 to 3.38, and varied with the trophic state of the lake. In eutrophic lakes these b values were significantly (P < 0.001) lower than in oligotrophic or mesotrophic lakes. Relationships between the b values and phosphorus concentrations were logarithmic: b ¼ 1.37-0.13 log (PO 4 -P); total length, fork length and standard length were linear (in all cases: r 2 > 0.95). In most of the lakes, populations consisted of females, with the exception of Pamvotis, Doirani and Koronia lakes where a small proportion were males.
Population structure and growth parameters of Prussian carp (Carassius auratus gibelio) were studied in 12 freshwater ecosystems of the Donbass region (Eastern Ukraine). These ecosystems differed significantly with respect to their surface area, water transparency and annual concentrations of phosphorus and nitrogen. Amongst the studied ecosystems, diploid males and females as well as a smaller percentage of triploid females were found. The population structure of C. a. gibelio varied significantly in terms of the percentage of triploids and sex ratio amongst diploids. A considerable proportion of triploid females ([10%) was found in four ecosystems with intermediate surface area (38-50 ha) and relatively high growth rate of specimens. The sex ratio amongst diploids was significantly femalebiased in seven of 12 ecosystems, including those where triploids were present in considerable numbers. The growth parameters of Prussian carp were significantly correlated with ecosystem characteristics, but the growth patterns of diploids and triploids were not significantly different from each other. The restricted distribution of triploid specimens suggests that the triploid form might counter diverse environmental challenges, whereas the diploid form of Prussian carp seems to be efficiently adapted to a wide range of ecosystem conditions.
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 (L(S)) (25.04 cm) than females (29.75 cm) and had lower exponent b of the L(S) 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.
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