Treatment methods

Bath

A bath treatment is carried out by stopping the flow of water to a tank and adding the chemical. After a predetermined amount of time, the water flow is restarted.  In tanks and ponds with a large volume, the level of the pond will be lowered to approximately half and the pond then treated. The water flow will then be turned on and the pond allowed to fill up and then run as normal. This reduces the amount of chemical used. Bath treatments are also used in cages, where a tarpaulin is pulled around the cage to enclose it and the chemical added. At the end of the treatment period the tarpaulin is removed.

Flush

A slug of chemical is added to a raceway or trough and allowed to pass down through the raceway with clean freshwater following behind. This is used in applications where it is impossible to turn the water off for a bath treatment due to limitations such as a lack of oxygen. This is used to good effect with eggs but with fish, their ability to swim through the chemical into the clean water, above gives variable results as the contact time cannot be guaranteed.

Drip

A constant supply of chemical at a low concentration (usually from a dosing pump, but sometimes form a simple device like a bucket with a hole in it) into  tank over a long period. Drips are sometimes with the antifungal chemicals used for eggs. Care must always be taken not to overdose the animals/ova, especially if the chemical used si one which can build up in the bloodstream (such as the copper in copper sulphate)

Dip

A quick (usually lasting less than one minute) treatment where fish are immersed in a chemical solution (usually of a high concentration). The easiest method for this is to net the fish from the tank and immerse the whole net and fish into the chemical. Used primarily for immersion vaccination, but also for the treatment of some parasites.

Swab

A piece of cloth or cotton wool is dipped into a high concentration of chemical and wiped of the fish. Impractical for large numbers of fish but sometimes used for the treatment of localised infections on valuable broodfish.

Injection

Injection of chemicals into the body of the fish is a process used by many farms for the administration of vaccines. Vaccines fall into one of four categories : 1. Intramuscular -where the chemical is injected into the muscle of the fish, improved results are gained if it is injected into the red muscle as the greater blood supply to this area ensures quick distribution round the body, 2.Intraperitonal - where the chemical is injected into the body cavity. 3. Intravenous - Injected into the bloodstream, which is largely impractical in most fish as locating the site is difficult, 4. Subcutaneous - Injected beneath the skin but not into the muscle. Both methods 1 and 2 give the best results with methods 3 and 4 not as effective. Injection of chemicals makes them act much faster than other types of administration and so are often used for valuable fish such as broodstock.

Oral

Mixing of chemicals such as antibiotics with the feed is an effective method of treating large numbers of fish. The feed is usually sprayed or coated with oil before mixing the chemicals in as this makes them stick to the pellets and prevents them being washed off as soon as the pellet hits the water. As appetite is often reduced as a result of infections, there can be difficulties in getting the fish to eat the medicated feed if treatment is left too late. This is particularly so with some antibiotics such as sulphonimides which impart an unpleasant flavour to the fish and so reduce the appetite even more.