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 ruti lus 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 plasti c characters were intermediate, with the hybrid index being 51.7 % and 51.2 %, resp. The length-weight relationship of the hybrid was simila r to that in the parental species. The regression coefficients varied according to the duration of the vegetative season and to the degree o f sexual maturity. The age of hybrids was 5-6 years which corresponds to reproduction in 1987 up to 1988.