• abnormalities;
  • environmental pollution;
  • freshwater fish;
  • osteological development;
  • vertebral column

This study was designed to describe normal axial skeletal structure in common roach Rutilus rutilus from putative unaffected environmental conditions, and the occurrence of skeletal malformations in the fish from an area under radiation contamination. Specimens were collected from water bodies of the Techa Cascade Reservoirs located near the Mayak atomic industry plant in the River Ob’ drainage, Chelyabinsk Province, Russia. One sample was collected from Lake Irtyash, a reservoir of drinkable water, supplying the town of Ozersk, and the other one from a technical reservoir which is a storage of liquid radioactive waste from Mayak and characterized by high radioactive contamination (mostly 90Sr and 137Cs). A comparison was made with historical material collected from the River Ob’ before the middle of the 20th century, i.e. before the environment became affected by radioactive contamination. A high number of abnormalities of the axial skeleton were detected in both Mayak samples, in 94 and 97% of examined specimens, in contrast to about 20% in the historical specimens. The abnormalities were in both the unpaired fins and the vertebral column, including the caudal complex and included supernumerary elements, fusions, deformities and displacement of the elements. Most axial skeleton abnormalities, however, were minor, such as splitting, shortening or deformation of spines. Severe defects, such as extensive scolioses, lordoses and kyphoses, were not found. The causes of the abnormalities were not identified in this study, but the high incidence of malformations may be attributed to genetically determined imbalance during development. The almost equal distribution of abnormalities among the fish from non-contaminated and radioactive contaminated reservoirs may be explained by either recent gene flow within the population of R. rutilus in the River Techa system or the effect of unknown unfavourable environmental factors such as chemical pollution.