Physiological action of dissolved organic matter in rainbow trout in the presence and absence of copper: Sodium uptake kinetics and unidirectional flux rates in hard and softwater

Aline Y.O. Matsuo, Richard C. Playle, Adalberto L. Val, Chris M. Wood

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We investigated the physiological effects of dissolved organic matter (DOM) on sodium (Na +) transport in juvenile Oncorhynchus mykiss (∼2.5 g) in the presence and absence of simultaneous acute exposure to copper (Cu 2+; 0, 70, and 300 μg l -1). Trout were acclimated in either hardwater (∼1000 μM Ca 2+) or softwater (∼100 μM Ca 2+), and DOM was tested at approximately 8 mg C l -1 using a natural (NOM) and a commercial (AHA) source. Ion transport was evaluated based on kinetics estimates (maximum Na + uptake rates, J max; substrate affinity, K m) and unidirectional flux measurements (J in, J out, J net). J max was higher and unidirectional flux rates were greater in softwater-acclimated trout. Fish exposed to DOM alone in hardwater exhibited an increased Na + transport capacity indicated by both the kinetics (67% higher J max for AHA) and J in measurements (153% higher for AHA and 125% higher for NOM). In softwater, the effects of DOM alone on kinetic parameters and unidirectional flux rates were negligible. Cu 2+ affected Na + uptake by a mixed-type inhibition (both non-competitive and competitive). In hardwater, only K m was increased (i.e., affinity decreased), whereas in softwater, K m was increased and J max was decreased, with more marked effects at the higher Cu 2+ level. In hardwater, the stimulatory effect of AHA on J max persisted even in the presence of 300 μg l -1 Cu 2+, whereas both AHA and NOM prevented the increase in K m caused by Cu 2+; these effects were reflected in J in measurements. In softwater, AHA helped to protect against the increased K m caused by high Cu 2+, but there was no protection against the inhibition of J max. Unidirectional flux measurements indicated that in softwater, Cu 2+ inhibited J in at 70 μg l -1, whereas at 300 μg l -1 Cu 2+, J out was also stimulated. Fish were more affected by Cu 2+ in softwater, as indicated by the inability to control diffusive losses of Na + and a reduced ability to take up Na +, but in the presence of DOM, losses were better controlled at the end of 6 h exposure. We conclude that DOM has direct effects on the gills, as well as protecting fish against acute Cu 2+ toxicity. This occurs because DOM complexes Cu 2+, and because it acts on the transport and permeability properties of the gills. These effects differ depending on both water hardness and the nature of the DOM source.

Original languageEnglish (US)
Pages (from-to)63-81
Number of pages19
JournalAquatic Toxicology
Issue number1
StatePublished - Oct 18 2004



  • Copper
  • Dissolved organic matter
  • Fish
  • Na transport
  • Toxicity

ASJC Scopus subject areas

  • Aquatic Science

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