The possible influence of trophic state on the life traits of a Greek endemic cyprinid fish (Rutilus ylikiensis) was investigated in two contrasting lakes. Lysimachia Lake is a eutrophic and very polluted shallow lake, while Trichonis Lake is an oligotrophic to mesotrophic, clearer, and deeper lake. Significant differences between the lakes were found in relation to the life history traits of the fish. In the eutrophic lake, fish achieved higher age and spawned more but smaller eggs than in the oligotrophic lake. In the eutrophic lake, females achieved higher age than males and the overall sex ratio of males: females was 1:3.42. The extrapolated mortality rate for females was significantly lower than that for males. Females were significantly heavier than males of the same length. In contrast to the above, no such differences between sexes were found in the oligotrophic lake.