The classic cartoon image is of a cat with its paw in the goldfish bowl hoping to catch a tasty morsel. If you have aquatic fish and a cat don't let it anywhere near them. The problem is the antibiotics given to breeding fish in their breeding tanks often in Asia. The fish have become resistant to the drugs and as a result are more disease ridden according to the Journal of Fish Diseases. The danger is that a cat eats the fish and is then affected by the disease and can die. Similarly humans should use gloves when handling tropical fish and keep them away from babies and the elderly...not forgetting the cat!