Acute effects of chemically dispersed crude oil on gill ion regulation, plasma ion levels and haematological parameters in tambaqui (Colossoma macropomum)

The main goal of this study was to investigate the toxicological effects of the chemical dispersant Corexit 9500, crude oil and the combination of the two components in the form of chemically dispersed crude oil (CO + DIS) on the ion regulation of the tropical fish tambaqui (Colossoma macropomum). Gill ion regulation was evaluated on the basis of unidirectional flux measurements (influx-J(in), efflux-J(out) and net flux-J(net)) of Na(+), Cl(-) and K(+). Plasma ion composition, haematocrit, haemoglobin and glucose concentrations in the blood of tambaqui were determined by classical methods. The exposure of fish to chemically dispersed crude oil promoted a significant increase in J(out) Na(+) across the gills, which, together with the inability of fish to stimulate Na(+) uptake to compensate for these losses resulted in significantly higher J(net) Na(+) outward, particularly within the first 3 h of exposure. Increased outward J(net) Cl- was also seen in fish that were exposed to dispersed crude oil, whereas outward J(net) K(+) was only increased at crude oil dispersed in higher concentration of Corexit 9500. Plasma Na(+) and Cl(-) concentrations decreased between 6 and 12 h of exposure, whereas Ca(2+) concentrations remained significantly lower than those of the control group over the entire experimental period. There were significant increases in plasma K(+) concentrations and in the haematocrit after 6 and 24 h of exposure to dispersed crude oil, suggesting significant changes in the permeability of the erythrocytic membrane. Collectively, our results suggest that chemically dispersed crude oil promotes a more extensive impairment of gill ion regulation, in addition to changes in plasma ion levels and blood parameters, in tambaqui compared with exposure to Urucu crude oil or Corexit 9500 alone. Thus, in the event of an oil spill in Amazonian waters, the chemical dispersion of Urucu crude oil could represent a great risk to tambaqui, challenging their ability to maintain ionic and osmotic gradients in native ion-poor waters. (C) 2010 Elsevier B.V. All rights reserved.