Salinity Tolerance and Gill Plasticity of Arctic Grayling (Thymallus arcticus): Physiological and Environmental Perspectives

Arctic grayling (Thymallus arcticus) are salmonids that have inhabited only freshwater environments in post-glacial North America, but unlike other salmonids do not undergo smoltification.  With expanding oil industry, the threat of incidental saline water release increases the likelihood of acute salinity exposure for grayling. We compared the physiological responses and survivability of Arctic grayling and rainbow trout (Oncorhynchus mykiss) to tolerate an acute transfer to higher saline waters. Arctic grayling and rainbow trout were placed directly into 17ppt salinity and sampled at 0, 24 and 96h. Serum sodium, chloride, and osmolality levels significantly increased in grayling at both 24 and 96h time points while trout were able to compensate the osmoregulatory disturbance by 96 hours.  NKA enzymatic activity, cortisol and NKA expression responses to salinity were also compared. Our results demonstrated a substantially reduced salinity tolerance in grayling. This study reveals a significant morphological rearrangement of the gills of grayling as demonstrated by the growth of an interlamellar cell mass (ILCM) by 24 and persisting at 96h. We demonstrate and quantify the appearance of the ILCM as a response to high salinity, although the functional significance remains to be demonstrated.

Supported by an NSERC Discovery Grant to GGG.