To add to this, most of the tissue we feed to our tanks contains some level of copper. Copper is required in small amounts, its when the molecule becomes present in larger concentrations that invert poisoning occurs.
And a little proof, read the copper content of 1 ounce of mixed mollusks and squid species.
http://nutritiondata.self.com/facts/...roducts/4197/2
Even more proof:
Copper is the oxygen binding molecule in many invertebrate species hemocyanin protein (Their form our our iron dependent hemoglobin protein).
http://en.wikipedia.org/wiki/Hemocyanin