HISTOMORPHOLOGICAL CHANGES IN EPIDERMAL STRUCTURE OF JUVENILE ARCTIC CHARR (SALVELINUS-ALPINUS L) SUBJECTED TO SUSTAINED EXERCISE

Groups of sexually immature juvenile Arctic charr (Salvelinus alpinus L.) were subjected to exercising regimes equivalent to either approximately 0.0 (control), 1.0, or 2.0 body lengths per second for 63 days. The effects of the different treatments on the epidermal structure of individual fish were examined. Epidermal thickness, measured in micrometres, did not vary between treatments, but fish exposed to a water current equivalent to 2.0 body lengths/s had increased numbers of epidermal cell layers compared with control fish. There were no differences in the numbers of mucous cells per millimetre of cell layer irrespective of the treatment employed, but the increase in the numbers of cell layers exhibited by exercised fish appeared to have resulted in an increase in the numbers of mucous cells per square millimetre of cross-sectional epidermal area (i.e., cell concentration). The superficial mucous cells were significantly larger in exercised fish than in control fish. There were no differences in the sizes of the underlying mucous cells among treatments. The variations in epidermal structure could not be ascribed to differences in individual growth parameters, but appeared to be a consequence of the different exercising regimes imposed upon the fish.