- Small, white spots appear on the head, body and fins. This is called Whitespot (Ichthyophthirius).
- Sustained loss of appetite. Newly introduced fish are slow to feed, while some fish consume only live foods. A basic water tester is used to check ammonia etc.
- Reddening of the skin or red streaks in the fins occur due to virus, ulcers (bacterial infection). This can be seen through microscopes and is incurable. For bacterial diseases, use an anti-bacteria or internal treatment. A prolonged salt bath will relieve osmoregulatory stress in the case of severe ulceration.
- Dull color (mucus), detached skin or fraying of the fin could be Mucus Hyperproduction. This is caused by Slime disease (parasites), poor water conditioners (high nitrogenous waste), flukes, and stress.
- Cotton wool effect on the body, columnaris, caused by fungus. An anti-fungus medication can be used or a salt bath (1 teaspoon per gallon) can be used.
- Scales are raised and fish are bloated. This is called Dropsy/Ascites. This can be thought of as a symptom rather than as a disease. This is associated with bacterial infections.
- Worms are seen hanging from the gills and fish are gasping. These worms are called gill flukes (Dactylogyrus genus). This is also a different parasite. So, anti-parasite drugs are used.
- A whitish film appears over the eye of the fish. This occurs due to poor water quality or poisoning (chlorine) or eye fluke.
Most disease organisms that affect pet fish are present in the newest aquariums. Majority of these are fungi, bacteria, protists and other pathogens. These can travel by air or water for long distances. Some of these can last long droughts.
Ammonia poisoning is due to the buildup of organic waste due to overfeeding, fish or plant deaths and decay, or improper cycling. Symptoms of these are sluggish behavior, panting and gill discoloration. Fish sometimes have to hang below the water surface. The easiest method of confirming ammonia poisoning is to test the water. This can be reduced by decreasing feedings, lowering the pH, making water changes, raising aeration and using zeolites.
Free chlorine that is present in tap water, especially in the form of chloramine, is toxic to fish. Chlorine affects the gills and leads to death by asphyxiation. This can be removed by boiling the water, vigorously aerating the water, letting the water remain for some days or by adding a water conditioner.
Nitrite/Nitrate poisoning is caused by activities like ammonia poisoning. This has the same symptoms as ammonia poisoning and can be tested by a nitrite/nitrate water test kit. The ideal method is to decrease feeding, raise the aeration in the water and make continuous partial water changes till the compounds are reduced.
Heavy metal poisoning
Heavy metal poisoning results from old pipes or metal in the fish tank. This is evident when fish gasp at the surface for air and breath rapidly. Tests are made to measure the amounts of heavy metals in the water. The ideal way to remove heavy metals is to use a reverse osmosis system. However, filtering the water through activated carbon and using water conditioners can be done.
Hydrogen sulfide poisoning
Hydrogen sulfide poisoning is caused by rotting debris and waste in the gravel of the tank. This gas is toxic. The first signs of its presence are an odor of rotten eggs and fish gasping at the water surface for air. The best method is to make a large water change by using a siphon to remove waste from the gravel. Partial water changes are made till the odor disappears and the fish return to normal swimming and breathing.