Americans are eating more fish these days, and half of it is farmed fish. The demand for fish has caused an explosion in fish farming and a search for new sources of fish feed. In this continuing food series, KPBS looks at how cattle are making their way into the diets of fish, and whether it raises health concerns.
Aquaculture is the term used for the farming of fish. Fish are hatched and raised in a net off the coast. This is considered an alternative to wild catch, which is often seen as a threat to depleting fish stocks.
However, critics say farming fish can be as detrimental to fish stocks as catching them. Fish typically eat other fish.
Dr. Jeffrey Graham is a marine biologist at Scripps Institution of Oceanography.
“For every pound of growth for a salmon, it takes about five pounds of fish that are caught and ground up and turned into pellets, or some kind of feeding mechanism to give to these fish. So five to one that’s a very stiff ratio,” he says.
This has led the fish farming industry to look for other food to feed fish.
Don Kent is President of Hubbs Seaworld, a San Diego aquatic research institute.
“There’s a lot of experimentation going on and we do it here on our species that’s looking to replace that fish meal in the diet with soy protein or other processing byproducts like beef or chicken byproducts," says Kent. "Basically waste in processing that can be turned around and used as a protein supplement to replace the fish meal.”
The U.S. slaughtered 34 million cattle last year. Only half the total weight of cattle is used in human consumption. The other half is cooked and processed and used in dog food and feed for chicken and fish.
David Meeker is with the National Renderers Association. Renderers are companies that process animal by-products.
“Some of these new diets might be supplemented with meat and bone meal instead of the fish meal and tallow instead of the fish oil,” says Meeker. Tallow is cow fat.
The food and drug administration banned feeding cattle by-products to other cattle in 1997 because of the threat of Bovine Spongiform encephalopathy (BSE), also known as mad cow disease. The same rules do not apply to fish feed. Last year, a new rule was added, and the FDA banned the use of cattle brains and spinal cords in all animal and fish feed because the highest concentration of infected material of diseased cattle is contained there.
According to some scientists, however, the rules may not go far enough.
A recent communication published in the Alzheimer’s Journal urges the FDA to ban all cattle material in fish feed. Dr. Robert Friedland is a professor of neurology at the University of Louisville and one of the authors of the paper.
“It is theoretically possible that a person who eats a fish that became infected from material from a cow could contract mad cow disease in that way," says Friedland. "The estimation of the risk is difficult. However, whatever the risk is I don’t think it’s a justifiable risk.”
In Greece, another group of scientists infected fish with BSE contaminated material. The scientists observed the fish two years after being infected, and found plaque in the fish’s nervous system similar to those seen in Alzheimer’s disease and Creutzfeldt-Jakob disease, the human variant of mad cow disease.
The European Food Safety Panel has banned using all cattle protein in fish feed.
Even if BSE is evident in fish, there is no evidence that it can be passed onto humans.
The FDA declined a taped interview with KPBS, but sent an email saying they believe the new regulation, which restricts the highest risk cattle by-products in feed, provides enough protection against the theoretical risk of BSE in fish.
The majority of cows with BSE have been found in the United Kingdom. According to the Centers for Disease Control, there have been three cows that have tested positive for BSE in the United States between 2003 and 2006.
