Background. A wide range of morphological anomalies, including abnormalities in scale shape and structure, have been described from a large number of fish species worldwide. Quite often, such reports linked the observed abnormalities to the quality of aquatic environment. The presently reported study was initiated to explore and categorize the abnormalities found in the scales of seven freshwater fish species of Czech Republic: Ctenopharyngodon idella (Valenciennes, 1844); Gymnocephalus cernua (Linnaeus, 1758); Hypophthalmichthys molitrix (Valenciennes, 1844); Hypophthalmichthys nobilis (Richardson, 1845); Leuciscus idus (Linnaeus, 1758); Perca fluviatilis Linnaeus, 1758; and Sander lucioperca (Linnaeus, 1758). The observed abnormalities are discussed in the context of contaminated aquatic environments with the intention to understand the aetiology of the abnormalities. Materials and methods. Samples were collected at 3 sites (ponds) in the Czech Republic. In total, 10 200 scales were collected, cleared in 1% potassium hydroxide, and observed under a light microscope. Four variables were measured for each scale: anterior–posterior length (major axis, MAA), dorsal–ventral length (minor axis, MIA), diameter of the focus in the centre of the scale, number of radial lines (radii) starting from near focus, and the ratio of major to minor axes were calculated as a measure of scale shape. Results. The anomalous scales, 63 in total, were collected from ten different body regions in seven species studied. They exhibited different shapes and sizes: 30 scales showed severe anomalies and 33 only slight ones. Based on the MAA : MIA ratio, the majority of the scales examined had a narrow to rectangular or broad to squarish shape. Elongated scales were only obtained from H. molitrix, H. nobilis, and C. idella. There were one square-shaped and 8 rectangular-shaped scales in G. cernua, 3 and 6 in P. fluviatilis, and 2 and 1 in S. lucioperca. Conclusion. The presently reported cases of fish scale abnormalities should direct the future work on the relations between the state of the environment and fish health. Another interesting question to answer would be to determine whether or not the removal of abnormal scales would lead to replacement by either normal or abnormal scales.

fish, scale abnormality, adverse environment, Cyprinidae, Percidae