The spawning season of chub,Leuciscus cephalus, in western Greece starts in January‐February when males are aged at least 2 + and females 3 + (rarely 2 +) years. In the R. Ermitsa (Achelos R. basin) a population is reported with fingerling adult males with developed gonads and breeding tubercles at a size of 42 72 mms.l.Leuciscus pleurobipunctatusbreeds between February and the first half of May, when males are aged at least 1 + and females 2 + (sometimes also 1 +); their life span is about 4 years. L.cephalus × L. pleurobipunctatushybrids were found in the R. Ermitsa (five specimens) and R. Louros (one specimen). In the former the contemporary presence of adult fingerling male chub, the smallest adults of L.pleurobipunctatus, and hybrids between the two species, may be related to channel width and the human interference which has resulted in considerable disturbance of the habit