By Cletus M. Sellers Jr., Alan G. Heath, Michael L. Bass
Water Research, Volume 9, Issue 4, April 1975, Pages 401-408, ISSN 0043-1354, DOI: 10.1016/0043-1354(75)90185-2.

Changes in buccal and opercular pressure amplitude, as well as ventilation and coughing frequency were monitored in rainbow trout using catheterization of respiratory cavities and pressure transducers. One or more of the ventilatory parameters measured were found to change under toxicant stress at concentrations of copper or zinc at or below the LC 50. Possible synergistic effects were indicated when the two metal ions were tested together.
Serial analyses of arterial PO2 and pH in fish exposed to copper and zinc individually at concentrations approximating the LC 50 showed that environmental zinc produced a sharp decrease in both PO2 and pH. Copper, however, caused little effect other than a transient increase in pH. The toxic action of the two metals in low concentrations thus may not be the same.

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