The epidermis structure of the studied specimens of Cottus gobio and C. poecilopus from the Morava watershed showed important differences. We noted a lower number of sacciform secretory cells in C. gobio, and also differences in relation to reproductive activity (the decrease in the number of secretory cells during the spawning period in both species). Significant differences were found in the erythrocyte count (1.90 ± 0.15 T.l–1 in C. gobio and 1.57 ± 0.07 T.l–1 in C. poecilopus), whereas the leucocyte count did not differ. A three-day-long exposure in higher temperature and lower oxygen saturated water conditions caused a marked increase in both blood parameters. These differences can be related to the distant physiological and ethological requirements of the species.
Growth in length and weight, based on a combination of scale annulus interpretation and back-calculation using the Fraser-Lee model, was studied in male and female barbel, Barbus barbus, from a section of the River Jihlava sampled in 1999–2001. Results were compared with growth data obtained with similar methods in 1976, prior to construction and functioning of a hydropower scheme complex, and during the period of the scheme’s partial operation (1980–1984). Recent growth rate, under seemingly fully-stabilised environmental conditions and complete adaptation of the barbel population, showed the highest distinct sexual dimorphism in growth rate was also confirmed, with females growing faster than males, though to a lower extent than recorded both during previous periods and from several other localities. Further, upon comparison of back-calculated lengths for previous years of recently tagged-and-recaptured fish (1999–2001) with observed lengths directly measured at corresponding ages, no significant differences were overall found between the results obtained by either method in most age groups. Finally, the linear Fraser-Lee model proved a sufficiently accurate and practical method for back-calculating lengths for previous years of life also in barbel.