Researchers at the University of Louisville have published a study saying fish farming techniques could lead to more cases of mad cow disease.The act of feeding rendered cow body parts to other cows is thought to have caused the spread of mad cow disease in cows and the humans who eventually eat them. Now that the practice has been banned in many countries, the rendered materials are increasingly being fed to commercially grown, or farmed, fish.Study co-author Robert Friedland says no cases of mad cow have been linked to fish, but they are physiologically capable of contracting and transmitting the disease."The fish have a protein which could be infected by the material from cows," he says. "So it is conceivable that fish could develop the disease themselves if they consume infected material."The paper comes before a new FDA rule that blocks the feeding of rendered cows to certain animals, but not fish.