The health of fish is directly related to the quality of the water in which they live. In fact, most diseases can be avoided once the fish are well adapted, if the aquarium is well treated and kept stable. The prophylaxis and treatment of fish at the Vasco da Gama Aquarium is the responsibility of the Chemistry and Pathology Office which, with the collaboration of the Aquatic Animal Pathology Service of the National Institute for Veterinary Research, has been developing a remarkable work regarding the study of fish diseases.