Like any other animal, tropical fish can become ill and suffer from a disease. If you want to find out whether or not a fish is healthy you should look out for signs of diseases. Not only should you check your own fish, but also a fish you might want to buy from a friend or in a store. Buying a sick fish will most likely cause the disease to spread in your fish tank.
Bacterial Diseases:
Bacterial diseases often need to be treated with antibiotic medications. Fish infected with bacteria often develop bulging eyes, ulcers and open sores. One bacteria causes a disease called mouth fungus that looks like a fungal infection on the mouth. Other signs of a bacterial infection include a lose of appetite, hollow belly, erratic swimming, and disintegrating fins.
Physical Ailments: Physical Ailments are often the result of the environment. Poor quality water conditions can lead to fish gasping, not eating, jumping out of the tank, and more. Tank mate problems can result in nipped fins and bite wounds.
Fin Rot: Fin rot is one of the most common diseases in aquarium fish. Luckily, it's also the most preventable. It's also usually curable, but if left untreated, it could kill your fish and infect all others in the tank. When infected, you'll notice your fish's fins turn white at the edges, and overtime will become red and inflamed. You'll also notice bloody patches as more of the fish's fin is eaten away.
Fungal diseases: is one of the most commonly contracted disease in a fish, it's symptom includes white spots showing up in the skin of the fish. This is most commonly observed especially during stressful period for the fish, as white spots indicates that your fish is weakened by stress. Isolate them to a new tank and monitor them closely, and try to help your fish relax by not aggregating it.