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      Reduced salinity tolerance in the Arctic grayling ( Thymallus arcticus) is associated with rapid development of a gill interlamellar cell mass: implications of high-saline spills on native freshwater salmonids

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          Abstract

          Arctic grayling were exposed to water conditions similar to industrial saline water spills. Grayling demonstrate a greatly diminished tolerance to seawater compared to euryhaline rainbow trout. Development of a novel response, a gill interlamellar cell mass, occurred within 24 hours in response to 17ppt (50% seawater) exposure.

          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.

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          The multifunctional fish gill: dominant site of gas exchange, osmoregulation, acid-base regulation, and excretion of nitrogenous waste.

          The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.
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            RNase H-dependent PCR (rhPCR): improved specificity and single nucleotide polymorphism detection using blocked cleavable primers

            Background The polymerase chain reaction (PCR) is commonly used to detect the presence of nucleic acid sequences both in research and diagnostic settings. While high specificity is often achieved, biological requirements sometimes necessitate that primers are placed in suboptimal locations which lead to problems with the formation of primer dimers and/or misamplification of homologous sequences. Results Pyrococcus abyssi (P.a.) RNase H2 was used to enable PCR to be performed using blocked primers containing a single ribonucleotide residue which are activated via cleavage by the enzyme (rhPCR). Cleavage occurs 5'-to the RNA base following primer hybridization to the target DNA. The requirement of the primer to first hybridize with the target sequence to gain activity eliminates the formation of primer-dimers and greatly reduces misamplification of closely related sequences. Mismatches near the scissile linkage decrease the efficiency of cleavage by RNase H2, further increasing the specificity of the assay. When applied to the detection of single nucleotide polymorphisms (SNPs), rhPCR was found to be far more sensitive than standard allele-specific PCR. In general, the best discrimination occurs when the mismatch is placed at the RNA:DNA base pair. Conclusion rhPCR eliminates the formation of primer dimers and markedly improves the specificity of PCR with respect to off-target amplification. These advantages of the assay should find utility in challenging qPCR applications such as genotyping, high level multiplex assays and rare allele detection.
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              Structure and function of ionocytes in the freshwater fish gill.

              Freshwater fishes lose ions to the external medium owing to the steep concentration gradients between the body fluids and the water. To maintain homeostasis, they use ionocytes to actively extract Na(+), Cl(-), and Ca(2+) from the dilute external medium and excrete acidic (H(+)) or basic (HCO(3)(-)) equivalents by specialized cells termed ionocytes that are responsible for transport of ions. Freshwater fishes have evolved diverse approaches to solving these similar ionic and acid-base problems. In the few well-studied species, there are clearly different patterns in the physiology and morphology for ionocytes in the gill. In this review, we describe the varying nomenclature of ionocytes that have been used in the past 80 years to allow direct comparison of ionocytes and their common functions in different species. We focus on the recent advancement in our understanding of the molecular mechanisms of ion and acid-base regulation as represented by ionocyte subtypes found in rainbow trout, killifish, tilapia and zebrafish gill. Copyright © 2012 Elsevier B.V. All rights reserved.
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                Author and article information

                Journal
                Conserv Physiol
                Conserv Physiol
                conphys
                conphys
                Conservation Physiology
                Oxford University Press
                2051-1434
                2016
                23 March 2016
                : 4
                : 1
                : cow010
                Affiliations
                Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
                Author notes
                [* ]Corresponding author: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9. Tel: +1 780 492 1276. Email: greg.goss@ 123456ualberta.ca

                Editor: Steven Cooke

                Article
                cow010
                10.1093/conphys/cow010
                4922264
                27382473
                2c764969-4ed6-42c2-af9f-3cffb7160d0c
                © The Author 2016. Published by Oxford University Press and the Society for Experimental Biology.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 17 November 2015
                : 5 February 2016
                : 19 February 2016
                Page count
                Pages: 11
                Funding
                Funded by: Natural Sciences and Engineering Research Council (NSERC)
                Award ID: 203736
                Categories
                Research Articles

                gill plasticity,osmoregulation,salinity,sodium–potassium atpase,thymallus arcticus

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