Phenotypic plasticity in brook charr: changes in caudal fin induced by water flow

In the field, juvenile brook charr Salvelinus fontinalis inhabiting high-velocity water were found to have larger caudal fins and more slender bodies than those inhabiting low-velocity water. Young-of-the-year S. fontinalis were reared in either a high- or low-velocity treatment for 16 weeks and their morphology was measured bi-weekly. From the second to fourth weeks of the experiment onwards, fish reared in the high-velocity treatment had larger maximum caudal fin heights and deeper caudal peduncles than fish reared in the low-velocity treatment. This study demonstrated that the morphological variation in caudal area exhibited by wild juvenile brook charr from microhabitats differing in water velocity could be a consequence of phenotypic plasticity in response to hydrological conditions.