Smolt characteristics of small first‐time migrant, and resident Arctic charr,Salvelinus alpinus(L.), from a river system in northern Norway

摘要

AbstractSmolt characteristics were investigated in sympatric anadromous and resident Arctic charr.Salvelinus alpinus(L.), of a similar size (11‐20 cm), A group of first‐time migrant anadromous charr was caught while descending the Hals River and two groups of resident conspecifics were caught in Lake Storvatn. one before, and one after, the sea‐run of anadromous fish had terminated. When sampled immediately after capture in fresh water the anadromous group had a higher proportion of fish visually classified as smolts. and these charr had higher gill Na+‐K+ATPase activity, higher densities of developed chloride cells in the gills, a lower condition factor, and lower plasma osmolality, than resident fish. When exposed to sea water (33o S), only minor differences in mortality and plasma electrolyte levels were observed between anadromous and resident fish, average values of plasma osmolality and chloride concentrations being 377 mOsm and 169 mM and 387 mOsm and 174 mM, respectively. The results suggest that the first‐time migrant Arctic charr had undergone some of the physiological changes that are considered typical for a parr‐smolt transformation before they left fresh water. Such changes did not appear to have occurred in sympatric, resident, fish of a similar size. The parr‐smolt transformation in the first‐time migrants may, however, have been incomplete, because the fish did not appear to have the ability to rapidly re‐establish osmo‐ and ionoregutatory homeostasis after direct tr