The best sources of aquarium fish are aquatic societies and specialist aquarium shops. Look for specimens with appropriately healthy colors and a well-defined example of any distinguishing pattern. They should have well-proportioned bodies, and should appear to swim effortlessly.
Be watchful for any evidence of disease, such as ulcers, fin damage, :cloudy eyes, and breathing or swimming abnormalities. Try to observe the fish while they are feeding; those that are reluctant to take food may be in poor health.