MORPHOMETRY OF RUTILUS-RUTILUS X ABRAMIS-BRAMA HYBRID FROM THE MOSTISTE RESERVOIR (MORAVA RIVER SYSTEM, CZECH-REPUBLIC)

During ichthyological monitoring of the Mostiste Reservoir in 1992 and 1993, an increased occurrence of the intergeneric hybrid Rutilus rutilus x Abramis brama was found. Proportion of the hybrid in samples of fish caught ranged between 8 and 11 %, and in the set of the parental species, it was 11-29 %. Values of differentiating meristic and plastic characters were intermediate, with the hybrid index being 51.7 % and 51.2 %, resp. The length-weight relationship of the hybrid was similar to that in the parental species. The regression coefficients varied according to the duration of the vegetative season and to the degree of sexual maturity. The age of hybrids was 5-6 years which corresponds to reproduction in 1987 up to 1988.