Routes of administration
Aim to treat fish, not the water. Use the least stressful method of treatment to achieve effective therapeutic levels of medication. Administration methods include
In-water
In-feed
Gavage
Injection
Topical application.
In-water medication
This route is most suitable for the treatment of external parasite and fungal infection, though some chemicals may be absorbed through the skin, gills or bowel (by drinking) Bacterial filtration systems will be damaged by some drugs (e.g. antibacterial drugs) unless treatment is carried out in an isolation facility with careful monitoring of water quality. Ozone and ultraviolet carbon removed before in-water administration, since they may reduce the efficacy of the medication.
In-water medication may involve short timed dips in strong chemical solutions or a permanent bath involving low-dose medication of tank pond.
Antibacterial drugs
In-water administration of antibacterial drugs is problematic, since some drugs (e.g. oxytetracycline, quinolones) are chelated by hard water and drug uptake is uncertain. However, this may be the most practical method of treating fry and very small fish and sometime appears to be effective. Although most carrier compounds are inert, their effect on fish is often unknown and therefore only pure drug (100 % active ingredient) shout be used, if available. Some chemicals alter the pH of the water when in solution and this may affect their uptake. To minimize the development of drug-resistant strains of bacteria, treatment using antibacterial drugs by in-water medication should be restricted to high-strength short dips.
Short dips
Short dips are stressful. since they involve netting, water used for the dip treatment should be taken from the aquarium or pond of origin. Antibacterial dips also obviate any harmful effect on the biological filter. Some concentrated dips (e.q. organophosphates) may be harmful to the operator.
Permanent baths
Permanent baths are less stressful to the fish but the effects of long-term exposure to some chemicals are unknown. Many fish keepers do not know the exact volume. Of their own ponds and in such cases miscalculation and overdosing can cause problems, requiring large volumes of water to be changed immediately. Where possible, baths should be filled using an accurate water meter (Figure 30.2), sine it is the total volume of water (in the pond and filter) that must be treated, not just the water in the pond. Formulae for calculating the size of tanks and ponds are give in Figure 30.3 The cost of in-water treatment of large volumes of water may be prohibitive.
Figure 30.2 A water meter is useful for measuring the total volume of water in large ponds and filtration systems. When performing partial water changes and to maintain the salinity at the same level, the correct amount of salt can be added according to the volume changed.
Absorption, timing and weather
-the rate at which different drugs are adsorbed is often unknown. As a general rule, non-polar compounds cross biological membranes faster than polar compounds
-Medications should be added early in the day so that fiat can be observed during the following 6 hours any sign of adverse reaction
-In outdoor ponds, avoid using chloramine-T in sunny weather since chemical breakdown is faster. Avoid using products containing formalin in hot weather since the chemical reduces dissolved oxygen levels.
Distribution
Chemicals should be distributed evenly. In small ponds, the diluted chemical can be applied evenly across the surface by using a watering –can with a rose sprinkler. This can be difficult to achieve in large ponds or lakes, where a boat with an outboard motor can be used to disperse the chemical throughout the water column. The chemical is slowly added to the water behind the propeller as the boat makes several traverses across