An appreciation of the significance of behavior patterns of fish can be as useful to the practitioner as for any of the more familiar domestic species. Veterinarians are trained in comparative medicine, and a logical clinical approach is warranted regardless of the species to which it is directed. The information provided here can serve to bridge the veterinarian's knowledge of other species with the problems encountered in a fish in the sense that knowing what to look for, or what you are looking at, can help put things in perspective. There is no substitute, however, for common sense. The experience a clinician gains through seeing many animals of many species will be as useful with piscine patients as with other animals.