title: Dissolved organic carbon from the upper Rio Negro protects zebrafish (Danio rerio) against ionoregulatory disturbances caused by low pH exposure.
abstract: The so-called "blackwaters" of the Amazonian Rio Negro are rich in highly coloured dissolved organic carbon (DOC), but ion-poor and very acidic, conditions that would cause fatal ionoregulatory failure in most fish. However these blackwaters support 8% of the world's ichthyofauna. We tested the hypothesis that native DOC provides protection against ionoregulatory dysfunction in this extreme environment. DOCs were isolated by reverse-osmosis from two Rio Negro sites. Physico-chemical characterization clearly indicated a terrigenous origin, with a high proportion of hydroxyl and phenolic sites, high chemical reactivity to protons, and unusual proteinaceous fluorescence. When tested using zebrafish (a model organism), Rio Negro DOC provided almost perfect protection against ionoregulatory disturbances associated with acute exposure to pH 4.0 in ion-poor water. DOC reduced diffusive losses of Na(+) and Cl(-), and promoted a remarkable stimulation of Na(+) uptake that otherwise would have been completely inhibited. Additionally, prior acclimation to DOC at neutral pH reduced rates of branchial Na(+) turnover, and provided similar protection against acid-induced ionoregulatory disturbances, even if the DOC was no longer present. These results reinforce the important roles that DOC molecules can play in the regulation of gill functions in freshwater fish, particularly in ion-poor, acidic blackwaters.
authors: Laboratory of Ecophysiology and Molecular Evolution, National Institute for Amazonian Research, Manaus, AM, Brazil.|Biosciences Institute, São Paulo State University - UNESP, Coastal Campus, São Vicente, SP, Brazil.
authors: Rafael M
authors: RM
authors: Duarte
authors: Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada.
authors: D Scott
authors: DS
authors: Smith
authors: Laboratory of Ecophysiology and Molecular Evolution, National Institute for Amazonian Research, Manaus, AM, Brazil.
authors: Adalberto L
authors: AL
authors: Val
authors: Laboratory of Ecophysiology and Molecular Evolution, National Institute for Amazonian Research, Manaus, AM, Brazil.|Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada.|Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
authors: Chris M
authors: CM
authors: Wood
mesh_terms: D000818:Animals; D001938:Brazil; D002118:Calcium / Q000032:analysis; D002244:Carbon / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000032:analysis; D045483:Rivers / Q000737:chemistry*; D012964:Sodium / Q000032:analysis; D013312:Stress, Physiological; D015027:Zebrafish / Q000254:growth & development*
chemical_list: D007477:Ions; D002244:Carbon; D012964:Sodium; D002118:Calcium