Is Copper the Answer?

Copper plays an important role in several aspects of fish physiology and, therefore, aquaculture.  Although copper has been identified as a factor in creating stronger fins and strengthening immune responses, the biochemical reactions involved are quite complicated; in fact, some of them have not been identified with certainty.  Copper, primarily in the form of copper sulfate, also has a long history in aquaculture for algae control and treatment of some external diseases.

An intriguing question that has arisen in recent years is the potential importance of copper in fish diets. Feeding studies with rainbow trout have shown that inclusion of additional copper in formulated feeds produces brighter coloration, stronger fins, and, apparently, greater resistance to several disease agents. In retrospect, the potential importance of copper in the diets of young salmonids makes sense. In natural, wild, settings some of the food items they consume are rich in copper. For example, stoneflies are relatively high in copper because their respiratory system is based on copper-containing hemocyanin, rather than iron-based hemoglobin.

Animals that have copper-based hemocyanin as the foundation of their oxygen transport and transfer system are far more common that many people realize.  Most mollusks and some arthropods have respiratory systems based on hemocyanin.  Many crustaceans and some insects are true “bluebloods” because of their hemocyanin-based respiratory systems. The evolutionary history of hemocyanin versus hemoglobin as the base for respiratory functions in animals is an interesting story. I suggest that readers with high curiosity levels should search out the rest of the story.  A simple online search will turn up plenty of references.

Research scientists at the Harry K. Dupree Stuttgart National Aquaculture Center recently initiated studies on the potential importance of dietary copper for improving the immune responses of channel catfish to columnaris disease, a disease caused by Flavobacterium columnare infections. Preliminary investigations provided sufficient evidence to indicate a relationship that needed further study. The initial reports based on this research will be completed soon and will provide the data for further discussion in the next issue of Aquaculture North America.    

— John Nickum