THE EFFECT OF SALINITY ON THE IODINE METABOLISM OF COASTAL AND INLAND PRICKLY SCULPINS, COTTUS ASPER RICHARDSON

Abstract

The lower mainland waterways of British Columbia are inhabited by two races of prickly sculpin, Cottus asper. The "coastal" race, which has a generally smooth skin, lives in the lower part of the rivers or estuaries and spends at least part of its life (particularly during the spawning season) under tidal conditions. The "inland" race, which displays a marked dermal "prickling", is confined entirely to freshwater, where it is found in scattered, more or less isolated populations, In freshwater the thyroid glands of both races are relatively quiescent, but with increasing salinity, particularly in a hyperosmotic environment, there is a marked increase in the uptake of tracer iodine by the thyroid and an elevation in the levels of circulating hormone. The inland fish have a greater ability than do the coastal fish to retain injected iodides in freshwater; in seawater the thyroids of the inland fish appear to be more active than do those of the coastal forms. The findings indicate a genetic divergence resulting in a relatively greater capacity of the inland fish to retain electrolytes.