Disease Help Center
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Q: Why is my fish sick and how do I prevent more illness?A: Probably 80-90% of diseases in captive fish can be prevented by avoiding stress. Stress weakens fishes' immune systems, leading to increased susceptibility to disease. Actually, diseases and pathogens are almost always present in tanks, but a healthy fish's immune system will prevent them from being a problem. Some of the most common stressors for captive fish are:
Q: Do I need a quarantine tank for new fish?A: Quarantining new fish is a good habit for all aquaria, but is not absolutely necessary for success. Quarantining is simply keeping a fish in a separate tank for long enough to be certain that it is disease free. Many beginners do fine without a quarantine tank, and object to the cost of another setup. A quarantine tank does cost more, but if a hobbyist has hundreds of dollars invested in fish, it is cheaper to have a separate quarantine tank than to replace fish killed by a newly introduced disease. Also, many of us become attached to fish and do not want to expose our pets to diseases from newcomers, no matter what the cost.
The purpose of quarantining is to avoid introducing new diseases to a stable system, and to be able to better observe new fish for signs of disease. A quarantine tank can also double as a hospital tank for sick fish. Hospital tanks are good because they lower the cost of using medicines and keep diseased fish separate from healthy ones. Quarantine is probably most important for saltwater tanks/reef systems because of the difficulty of treating diseases, or wild-caught freshwater fish because they are probably not disease-free. Quarantining itself can stress fish so be sure quarantine is as stress-free as possible.
To set up a quarantine or hospital tank:
Do not medicate quarantined fish "just in case." Only treat evident, definitely identified diseases. Treating all quarantined fish with a bunch of medicines will just lead to weakened fish and antibiotic resistant bacteria.
Once you are done with the quarantine, if you treated any especially nasty diseases, it is good to disinfect the tank and reestablish the filter. Chlorine bleach or strong saltwater (for freshwater) work well. Be sure all traces of bleach are rinsed off. Another good disinfectant is potassium permanganate (Jungle's Clear Water is one commercial way to get it).
Q: How do I avoid introducing diseases in the first place?A: Never buy sick fish from a store. Especially do not buy fish or plants from a tank if *any* fish in the tank shows any signs of disease or if there is medicine in the water (water is colored yellow, green, or blue). Store people may say the fish are fine, but if they were, why is the medicine in the tank? Also ask how long the fish have been in the store. New arrivals may be carrying diseases that have not shown up yet. It is better to wait a couple of weeks before purchasing the fish. If you must have a fish that just came in, be especially sure to quarantine it properly.
White spot disease (Ichthyopthirius multifiliis) is caused by a protozoan with a life cycle that includes a free-living stage. Ich grows on a fish --> it falls off and attaches to gravel or tank glass --> it reproduces to MANY parasites --> these swarmers then attach to other fish. If the swarmers do not find a fish host, they die in about 3 days (depending on the water temperature).
Therefore, to treat it, medicine must be added to the display tank to kill free-living parasites. If fish are removed to quarantine, parasites living in the tank will escape the treatment -- unless ALL fish are removed for about a week in freshwater or three weeks in saltwater systems. In a reef tank, where invertebrates are sensitive to ich medications, removing the fish is the only option. Some people think that ich is probably dormant in most tanks. It is most often triggered by temperature fluctuations.
Remedy: For most fish, use a medication with formalin and malachite green. These are the active ingredients in many ich medications at fish shops. Some products are Kordon's Rid Ich and Aquarium Products' Quick Cure. Just read the label and you may find others. Check for temperature fluctuations in the tank and fix them to avoid recurrences. Note that tetras can be a little sensitive to malachite green, so use it at half the dose.
Use these products as directed (usually a daily dose) until all of the fish are spot-free. Then dose every three days for a total of four more doses. This will kill any free-swimming parasites as they hatch out of cysts.
Another remedy is to raise the tank temperature to about 90 deg F and add 1 tsp/gallon salt to the water. Not all fish tolerate this.
Finally, one can treat ich with a ``transfer method.'' Fish are moved daily into a different tank with clean, conditioned, warmed water. Parasites that came off of the fish are left behind in the tank. After moving the fish daily for a week, the fish (presumably cured) can be put back into the main tank. The disadvantage of this method is that it stresses both fish and fishkeeper.
Remedy: First, fix the water and remove any fin-nipping fish. Change some water (25% is good) and add 1 tsp/gallon salt to promote healing. If bad water quality or an aggressive tankmate was the problem, that should be adequate. Healing will begin within a couple of days.
If it worsens, decide first whether it's fungal or bacterial. Fungal finrot looks like clumps of cotton on the fins and usually follows injury. It is commonly seen in African cichlids or fish that have injured themselves against decorations. Bacterial finrot is whitish, but not cottony (unless it's columnaris), and can be contagious. The fish then need to be removed from the tank and medicated.
Fungus: For fish large enough to handle, catch the fish, and dab malachite green directly on the fungus with a Q-tip. This is extremely effective. Repeat treatments may be necessary.
For small fish, a commercial fungicide such as Maroxy may work. For severe infestations, try a bath in methylene blue (enough so you can barely see the fish) until the fungus turns blue or for 20 min. If you add methylene blue directly to a tank, you will kill plants and trash your biological filter.
Bacterial: Antibiotic treatment in a quarantine tank. This is stressful for the fish, and doesn't always work, so be sure of what you are doing before you attempt it. If the fish is still eating, the best bet is an antibiotic food. Tetra makes one that works well -- just buy the one for bacterial diseases and follow the directions on the can.
If the fish is not eating, a bath treatment is necessary. A combination of Kaynamycin and Furanace usually works, especially for Columnaris. Again, treat in a separate tank and aerate heavily.
Larger fish can be netted and their injuries dabbed with mercurochrome (available at drug stores) or Betadine (iodine-based antibiotic also available at drug stores) to help prevent infection. Be sure to keep these chemicals off of the gills and eyes. For really small fish, put the affected fish in dilute methylene blue (pale blue) and 1 tsp/gallon salt in a separate tank. If you want to keep the fish in the main tank just add salt, as methylene blue will trash your biological filter.
Watch the fish to be sure injuries are healing cleanly, and repeat the mercurochrome dosage if necessary. If finrot or fungus sets in, see the above section on finrot.
Remedy: First, make sure water quality is optimal and reduce stress. Stopping carbon filtration may help as it can remove nutrients from the water. Then feed a vitamin-enriched food, paying particular attention to vitamin C supplementation.
For stubborn cases, some books suggest metronidazole (Flagyl) to eliminate Hexamita (a mildly pathogenic protozoan) from the lesions. Your mileage may vary with that one. Metrozole and Hex-a-mit are commercial medications with metronidazole.
To help, feed the fish pre-soaked or gel-based foods. Green foods are also helpful; peas in particular.
As with finrot, these disorders can also be caused by bacterial infection. Treatment is much the same. Use antibiotic food if the fish is eating, or add antibiotic to the water in a quarantine tank if the fish is too sick to eat.
Treat with an anti-parasitic medication such as copper or formalin/malachite green.