Abstract

Cupric ion (copper) is added to marine culture systems to control parasitic protozoans and algae. Mass fish kills from copper poisoning have occurred and the safe upper limit of copper concentration is reported to be 0.2 ppm. Mechanisms of intoxication, other than hypoxia, have been proposed but not identified. In an accidental copper poisoning, 610 cultured pinfish and other marine teleosts were exposed to an average copper concentration of 3.3 ppm over a 23 hour period. Signs of intoxication began 6 hours after introduction of copper. Deaths stopped 11 hours after copper concentration decreased to 0.2 ppm, and signs of intoxication stopped 6 hours after the last death. High K+ levels with failure of osmoregulation was found in dying fish. The possibility that potassium intoxication followed copper poisoning was further investigated in a controlled experiment by exposing sheepshead to 8.5 ppm copper for 12 to 17 hours. Stages of intoxication were defined based on behavior and posture. Fish were sacrificed at different stages of intoxication and blood and tissues collected. Twenty-one clinical values were measured and correlated with severity of intoxication. Increases in serum K+, PO₄ and total intracellular ion values correlated best, and the intoxication appears to be a potassium intoxication produced by cell damage and failure of osmoregulation by gills and kidneys. (Aided by Marineland of Florida.)

Notes

Two proposed mechanisms for copper toxicity in fish:

1. Cu irritates the gills --> mucous build-up on gills --> eventual hypoxia and death.
2. Fish ingest copper-containing brine shrimp.

Example of acute copper poisoning:

Copper poisoning:

Histopath - Gill - blunted, thickened villi

Liver - not damaged

Clin. path - Bilirubin)

SGPT) - Normal

Urea )

Creatinine )

Clinical signs - Lethargy --> indifference --> incoordination --> moribund -->death.

Intracellular changes occur with copper poisoning. K + intoxication is due to cell damage and kidney failure.

Copper poisoning can occur in the wild where stratification of water occurs. Cu builds up in the sediment at the pond bottom, then comes up and causes toxicity in fish when the water becomes homogeneous.