Below is a list of more common diseases found in tropical freshwater aquariums, their symptoms and suggestions on how to treat them.
1. Ichthyophthirius (Ich) - Ich (aka White Spot Disease) is probably the most common illness found in freshwater aquariums today. Ichthyophthirius multifiliis is a protozoan parasite that attacks the gills, fins and skin of a fish. The affected fish will have small white cysts that resemble grains of salt covering the body. Inside these cysts reside the adult protozoan themselves that attach to the fish much like a tick does to a dog. In this cyst form, medication is not effective. Over a period of time these cysts break open, fall to the bottom of the tank where they divide themselves up to 2000 times which are then known as tomites. This tomite stage, which lasts only 12 to 14 hours, is what is most vulnerable to medication. Because of this small window, it is important to treat the entire lifecycle of this pest, which is typically 10-14 days to assure it becomes under control.
Treatment and Prevention - ICH is always present in an aquarium and can never be 100% eradicated but one can reduce the risk of a major outbreak. Quarantining newly purchased fish for aprox 2 weeks before introducing into the main tank is an excellent practice to avoid exposing your tank to a possible outbreak. Assuring you purchase healthy fish is a good step as well. Avoid buying fish that are in an aquarium with sick tank mates. They may look healthy but they may be exposed to not only ICH but also a variety of other diseases you want to avoid. Also good tank husbandry, filtration and stable water conditions will help avoid an outbreak.
Suggested treatment is adding aquarium salt at 1tbs per 5 gallons of water, heat therapy by increase tank temperature to around 82F and frequent water changes of 25 to 40% daily replacing the salt lost each water change. Note, many species of fish such as catfish and loaches along with several other scales less fish are sensitive to salt and this dosage may have to be adjusted, be sure to factor in species you have in your tank. [b]
An alternative treatment if the above is not sucessfull after the suggested time is a product that contains malachite green and formalin (eg. Quick Cure, Rid Ich). Use as directed only continue treatment for 10-14 days instead of the 4 days or so suggested on the bottle. The reason I say this is that it is my opinion that companies only suggest around 4 days so that it is not completely cured. Thus you have to go buy more medication. Kind of a low blow if ya ask me. As well I suggest the temperature of the tank be raised to 82-84 F as this will speed the life cycle of the ICH and expose more tomites to medication at any givin time. I also suggest a hefty water change of 30-40% before the first dose of medication. This helps to remove any free-swimming tomites and assure water quality is optimal. Continue then with 25-30% changes daily for the duration of the treatment. Make sure carbon media is removed before treatment, as this will absorb the medication. Increasing filtration during treatment is suggested if possible. If you do have these type of fish, I suggest starting with 1/4 of the suggest salt and observe or not to use at all. Also be warned that Malachite Green will stain the silicone seals on your tank as well as porous ornaments so remove any you do not wish to have stained a pretty greenish blue. Once treatment is complete, you may place your carbon media back in if you use it, or use it to remove medication from the tank and discard.
2. Fin Rot - Fin Rot is a bacterial infection that will attack the fins and in severe cases other areas of your fish. Fins will look tattered and torn and will appear like they are rotting away. This disease is common in tanks with poor water quality or as a result of stress, fighting or bullying or a secondary infection to another illness. Minor cases are easily cured with Melafix and in moderate to severe cases, an antibiotic such as erythromycin (Maracyn) is suggested.
3. Body Fungus - Simply put, it is fungus that is on the body of your fish. It will appear as grey or white patches on the fins, body or gills that resembles cotton or wool. Fungus feeds by excreting an enzyme that digests organic matter leaving ulcers and if not treated can lead to death. It is common in aquariums with poor water quality and un-eaten food and is also common as a secondary infection as well. Using Melafix can cure treatment for minor cases and in more moderate to severe cases a bath in a malachite green solution of 4 teaspoons per gallon of water for 30 seconds. One bath usually does the trick.
4. Skin and Gill Flukes - A parasite that attacks the gills or the skin. Flukes are not visible to the naked eye and can be difficult to treat. Symptoms include excessive flashing or scraping on rocks and decor in the tank. The fish may show signs of erratic movement that can bring them to the point of exhaustion. The only sure way to diagnose is by skin scrape although one can come to a conclusion a fish is affected if no visible signs of parasites are present(anchor worms, lice, ICH, velvet etc) and the symptoms are evident. Total eradication is nearly impossible though copper sulfate or Potassium Permanganate are effective.
5. Velvet (Oodinium Pillularis) - This parasite is often confused as ICH, it looks more like a fine dust or powder that the salt like appearance ICH has. It attacks the body of a fish and gills and is very contagious and usually is found in tanks with poor water quality or sudden fluctuations in temperature. If not treated it can cause death. Treatment is similar to ICH and products that contain malachite green and formalin are effective.
6. Popeye - Popeye is caused by a few different ways, but all result in the eye protruding out from the head. Usually it is a result of a secondary infection or injury to the eye but can be the cause of a tumour, bad water quality, poor nutrition or virus. It is difficult to treat and use of a broad-spectrum antibiotic such as Minocycline (Maracyn 2) or Tetracycline can be effective.
7. Dropsy (Bloat) - This is a severe internal bacterial infection that attacks the organs of a fish. Symptoms include severe bloating of the abdomen cause scales to stick out and are quite grotesque in appearance. Unless the disease is caught in a very early stage, it is usually fatal and it is suggested to euthanize the fish rather than to treat. Treating with Phenoxethol or Clout in some cases is effective. Prevention however is your best defence against this disease. A good diet and optimal water conditions will greatly reduce the chance of this happening to your fish.
8. Cotton Mouth - Although it appears to be a fungus, Cotton Mouth disease is actually a bacterial infection. It will appear as a cotton like substance around the lips and mouth of the fish. Unless treated early, the toxins released and the difficulty of the fish being able to eat can be fatal. Melafix combined with a broad-spectrum antibiotic such as Tetracycline is suggested.
9. Hole in the Head (HITH) or Head and Lateral Line Erosion (HLLE) - Please see the article about this disease found HERE