Analyses were made of the fecundity of catfish from the rivers Vistula and Bug. Oocytes were counted, measured, and divided into groups depending on the presence of the corpus luteum. No statistically significant differences were found as to the oocyte numbers in the samples taken front different gonad sections. Luteal oocytes differed considerably as to their size, these differences being observed between particular females as well as for the same gonads. Number of the luteal oocytes depended on the fish weight and body length. The respective coefficients of correlation were 0.92 and 0.88, and these dependencies were expressed in a mathematical form.