You should always solicit veterinary advice to treat a sick or injured fish, but that does not mean you must sit idly by in the meantime. A few over the counter medications are available to treat minor fungal and bacterial infections, as well as some parasite infestations. Additionally, many health problems caused by poor water quality, stress or improper environmental conditions, are treatable at home.
Over the Counter Medications
Several medications and medicated foods are available to aquarists without a veterinary prescription. Some of these have proven helpful, but it is always best to consult with your veterinarian first to be sure you administer and dose the medication properly. However, if veterinary care is unavailable, these products may help save your fish. Some products treat specific bacterial, fungal or parasitic infections, whereas others treat a variety of common conditions. Always follow the manufacturer’s instructions.
Salt is helpful for improving the health of sick fish, and it may help resolve some minor illnesses. Salt encourages the development of a healthy slime coat, improves gill function and reduces the amount of nitrites your fish absorb. Additionally, raising the salt concentration slightly proves detrimental to many external parasites and fungi. Add approximately 1 tablespoon of aquarium salt for each 5 gallons of water -- do not use marine salt or table salt. Some fish, such as catfish of the genus Corydoras, are sensitive to salt levels, and should not be treated in this manner.
Many fish diseases are communicable, so it is always a good idea to remove sick fish from their permanent tank and place them in a small isolation tank. The isolation tank should have ideal water conditions for the species and be maintained at the upper end of your fish’s temperature range. The small size of the isolation tank makes it easier to administer medications, but, as it will remove any medications used, you must remove carbon filter media, before beginning treatment.
Periodic water testing should be part of your normal fish-keeping protocol, but it is especially important to analyze the water when your fish display symptoms of illness. Use a high-quality aquarium test kit to check the water’s pH, nitrites, nitrates, ammonia and phosphates. If you have a saltwater aquarium, you must also use a hydrometer to monitor the salinity. Make sure that all parameters are appropriate for the species that you keep. Adjust the water chemistry slowly to prevent shocking your pets. Often, re-establishing proper water chemistry results in improved health.
Stress inhibits immune function, so you must seek to limit it as much as possible. Moving sick fish to an isolation tank helps in this regard; but use this time to ensure the permanent tank’s environmental parameters are ideal. Ensure the tank’s temperatures are ideal and that it contains sufficient cover for the fish. Also consider whether social factors may cause stress among the inhabitants. For example, large aggressive bullies may stress smaller, timid fish, while schooling species may experience stress without suitable companions.