Abstract
Arctic grayling (Thymallus arcticus) are salmonids that have a strict freshwater existence in post-glacial North America. Oil and gas development is associated with production of high volumes of hypersaline water. With planned industrial expansion into northern areas of Canada and the USA that directly overlap grayling habitat, the threat of accidental saline water release poses a significant risk. Despite this, we understand little about the responses of grayling to hypersaline waters. 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 17 ppt salinity and sampled at 24 and 96 h along with control animals in freshwater at 24 h. Serum sodium, chloride and osmolality levels increased significantly in grayling at both 24 and 96 h time points, whereas trout were able to compensate for the osmoregulatory disturbance by 96 h. Sodium-potassium ATPase mRNA expression responses to salinity were also compared, demonstrating the inability of the grayling to up-regulate the seawater isoform nkaα1b. Our results demonstrated a substantially lower salinity tolerance in grayling. We also found a significant salinity-induced morphological gill remodelling by Arctic grayling, as demonstrated by the rapid growth of an interlamellar cell mass by 24 h that persisted at 96 h. We visualized and quantified the appearance of the interlamellar cell mass as a response to high salinity, although the functional significance remains to be understood fully. Compared with rainbow trout, which are used as an environmental regulatory species, Arctic grayling are unable to compensate for the osmotic stressors that would result from a highly saline produced water spill. Given these new data, collaboration between fisheries and the oil and gas industry will be vital in the long-term conservation strategies with regard to the Arctic grayling in their native habitat.
Highlights
The oil and gas industry is a socio-economic driver for both Canada and the USA, significantly impacting the overall gross domestic product of both countries (Honarvar et al, 2011)
Research on salmonid salinity tolerance is extensive, because this family is most well known for anadromous fish species that naturally make the transition from fresh to saline water at some point in their life cycle (Morgan and Iwama, 1991; Staurnes et al, 1992; Singer et al, 2002; Richards et al, 2003; Bystriansky et al, 2006; Larsen et al, 2008; Bystriansky and Schulte, 2011; McCormick et al, 2013; Dalziel et al, 2014)
We aimed to investigate the effects salinity exposure may have on Artic grayling, a threatened salmonid species that has had a strict freshwater existence in North American for the past 3–5 million years (Stamford and Taylor, 2004)
Summary
The oil and gas industry is a socio-economic driver for both Canada and the USA, significantly impacting the overall gross domestic product of both countries (Honarvar et al, 2011). In a recent review of hydraulic practices, Goss et al (2015) document a total of 113 spills of saline flowback fluid into flowing waters in the period 2005–2012 alone. These resource-rich geographical areas directly overlap with the habitat for threatened native freshwater salmonids [Arctic grayling, mountain whitefish, bull trout, westslope cutthroat trout, and inconnu (Northcote, 1995; Rieman et al, 1997; McPhail and Troffe, 1998; Howland et al, 2001; Walker, 2005; Costello, 2006; Rodtka, 2009)]. A sudden influx of highly saline water into a stream would pose an immediate osmoregulatory perturbation for aquatic organisms, and it is essential to understand the potential impacts on these native species, especially given that most regulatory guidelines are routinely based on the responses of the euryhaline rainbow trout (Environment Canada, 1990; USEPA, 2002)
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