title: Physiological basis for large differences in resistance to nitrite among freshwater and freshwater-acclimated euryhaline fishes.
abstract: Uptake of environmental NO2- by most freshwater fishes occurs at the gills where NO2- is actively transported into the blood by the Cl- uptake pathway. Some freshwater fishes do not concentrate NO2- in their plasma, regardless of environmental NO2- exposure and exhibit a high degree of resistance to NO2-. Recent studies indicate that freshwater-adapted killifish (Fundulidae: Fundulus heteroclitus) and European eel (Anguillidae: Anguilla anguilla) have no or minimal Cl- uptake activity at the gills relative to most freshwater fishes; rather, Cl- requirements are met in other ways (probably dietary). We hypothesized that different rates of Cl- uptake by the gill may explain the observed differences in NO2- uptake and consequent toxicity among freshwater fishes. Cl- influx rates of channel catfish (Ictaluridae: Ictalurus punctatus), a species that concentrates NO2- in the plasma and is sensitive to NO2-, and bluegill (Centrarchidae: Lepomis macrochirus), a species that does not concentrate NO2- in the plasma and is resistant to NO2-, were determined over a range of environmental Cl- concentrations. Channel catfish actively transported chloride into the plasma (Km = 155.6+/-101.2 micromol/L Cl-; Jmax = 414.9+/-51.4 nmol/g/h; +/-SEM). In contrast, bluegill exhibited no observable Cl- uptake. We placed our results and previously reported results in a phylogenetic context and concluded that differences in Cl- uptake mechanisms among groups of freshwater fishes may explain, in large part, the wide range of sensitivity to environmental NO2-. NO2- uptake determinations may also prove to be an easy screening method when studying the phylogenetic distribution and nature of Cl- uptake mechanisms in the gills of fishes.
authors.affiliation: Department of Biological Sciences, Clemson University, Clemson, South Carolina 29634, USA. jtmss@clemson.edu
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Tomasso
authors.forename: Martin
authors.initials: M
authors.lastname: Grosell
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002713:Chlorine / Q000737:chemistry / Q000493:pharmacokinetics*; D004351:Drug Resistance; D005880:Gills / Q000502:physiology*; D007059:Ictaluridae / Q000502:physiology*; D009573:Nitrites / Q000378:metabolism* / Q000633:toxicity*; D010473:Perciformes / Q000502:physiology*; D010802:Phylogeny; D014873:Water Pollutants / Q000378:metabolism* / Q000633:toxicity*
chemical_list: D009573:Nitrites; D014873:Water Pollutants; D002713:Chlorine