Tropical fish are like other species in many aspects, and that includes the fact that they have diseases. They can have fungus, eye problems and even tumors. Just as humans, cats or dogs may get cancer or other types of tumors, so can tropical fish.

The main difference is that treatment in fish is nearly impossible. Surgery is basically out of the question when it comes to tropical fish. Tumors such as Mesothelioma or Brain tumors generally show themselves as a lump under or on the skin of fish. Like in humans Mesothelioma occurs more often in males than in females and risk increases with age, Mesothelioma, though rare in fish, has had a number of miserable patients. In humans this disease as other tumors can be treated but it is not the case in our hobby. Fish do not get the appropriate treatment, maybe due to lack of suitable qualification or maybe because fish are (for some people) dispensable. These are a distinct bump or lump, as opposed to the white fluff of skin diseases, some times these lumps grow to enormous size that they are make swimming impossible. In such cases fish's quality of life declines and you may have to euthanize them. One type of tumor that does have some success with treatment is the kind that forms under the skin of the gill, causing it to remain open and some time to bleed. The cause of this is usually a thyroid malfunction. Remove the fish to a hospital tank, and add 1 milligram of potassium iodine for every gallon of water. Improvement can be slow, and the full course of treatment can take up to four weeks. Internal tumors can be quite advanced before the fish shows any signs, such as a swelling of the abdomen. These cases are invariably fatal, with the rapid growth causing the fish to lose its ability to swim or eat, at which time you should consider euthanasia.

Dropsy is caused from a bacterial infection of the kidneys, causing fluid accumulation or renal failure. The main Symptoms to dropsy are bloating of the body and protruding scales. To be accurate Dropsy isn't a disease itself, but actually a symptom of another underlying disease in the fish.  Dropsy in fish is somewhat contagious, it almost never can be healed and most afflicted fishes are either put down or isolated and allowed to live the remainder of their lives in quarantine.  Sometimes it's not contagious, but sick fish should be isolated, Fish may recover with no treatment and may die despite it, fish which do recover will see full improvement in under a week.   

1- High nitrates or internal bacterial infections - fish is absorbing water faster than it can eliminate- bloating of the body 

2- Kidney damage- overuse of medicines, inappropriate nutrition- bloating of the body and then Scales may be forced outward. 

There are medicines against dropsy that you can add to the tank water but to be honest those are not so effective. My favorite treatment is to give the fish medicated food. Make a 1% mixture of an antibiotic such as Chloromycetin or tetracycline and fish food (any type). Based on weight, 1% equals to add 100 mg antibiotics to 10g fish food. It is recommended to starve the fish before (for about to days) feeding them medicated food to make sure that they eat properly. If the fish became sick but still eating medicated fish food can help on rare occasions.   

1- Poor water conditions can be a major catalyst to the dropsy disease, perform water changes on a regular basis.

2- Check your water condition from time to time especially nitrate and ammonia.

3- Selecting the right fish food is obviously important to the health of your fish. Fish foods normally contain nutrients, trace elements and vitamins necessary to keep your fish in good health, these elements are essential so don’t underestimate the importance of purchase the right fish food.

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