Fish disease and antibiotics
Antibiotic baths or dips provide another route for the treatment of
bacterial fish diseases. However, baths and dips are not as effective as
medicated food or injections for treating systemic infections or
advanced ulceration. In general the best results come from antibiotic
Baths and dips are probably best used for surface infections such as
fin rot, bacterial gill disease and columnaris (cotton wool disease),
where short duration baths with high dosages may be useful.
There are conflicting reports about how effectively antibiotics are
absorbed into the blood from bath and dip treatments. The best absorbed
seem to be the nitrofuran antibiotics such as nifurpirinol and
nitrofurazone. The absorption of other antibiotics is generally poor,
which is why such treatments often fail against advanced and systemic
Antibiotics and biological filtration:
In general all antibiotics will have an adverse effect on nitrifying
bacteria, which means that treatment has to be carried out outside the
tank or pond. For longer-term bath treatments, this will severely
restrict the numbers of fish that can be treated if ammonia levels are
to be kept to an acceptable level without biological filtration. It is
important to test and monitor water quality during prolonged treatments.
Should water changes be required, the top-up water should contain the
appropriate amount of drug
It is important to use the purest possible drugs to avoid any side
effects from carrier compounds.
Chelation in hard water
Many antibiotics chelate divalent cations such as magnesium and
calcium, causing their inactivation. This is particularly the case with
all tetracyclines and quinolones such as oxolinic acid and enrofloxacin.
Higher doses of these drugs should be used when treating fish in hard
bath: 2 mg/litre for five days
25mg / litre for 15 minutes. Repeat twice daily for 3 days
bath: 13-120 mg/ litre
mg/litre - repeat every three days for up to three treatments
||66 mg/ litre.
Repeat every three days for up to three treatments
100mg / litre for 30 minutes
10mg/litre for 6 - 12 hours
2mg/litre prolonged immersion for 5 - 10
nitrofuran antibiotics are prohibited in the UK for use in
Note: When using oxytetracycline in long-term baths, be aware
that it is light sensitive and will start to turn brown as it
decomposes. If this happens a 50% water change should be carried out
immediately. Degraded tetracycline can be harmful to humans so avoid
contact by wearing gloves.