Bacterial disease and medicated food
When a bacterial disease has been diagnosed, one treatment option is
to use antibiotics. There are three main routes for antibiotic usage;
baths, injections and medicated food. Using medicated food is an option
that minimises handling and therefore stress although affected fish
may still need topical treatment for moderate to severe lesions.
One disadvantage of using medicated food is that it is not possible
to ensure that individual fish receive the right dose of medication;
indeed sick fish may not feed at all. The other problem with this method
is the limited choice of antibiotics in ready prepared food which
for hobbyists in the UK is restricted to oxolinic acid. It is possible
to top dress ordinary food with other antibiotics but this brings
with it the problems of palatability and the risk of antibiotics being
washed off the food before it is eaten.
Ready-prepared antibiotic foods
As already mentioned, in the UK oxolinic acid is the only antibiotic
treated food available to hobbyists. Unfortunately, because of previous
overuse and misuse, there is a very high level of bacterial resistance
to oxolinic acid. Other antibiotics are available in commercial fish
foods used to treat food fish such as salmon and trout, but my
understanding is that these are not available to hobbyists. All
ready-prepared medicated food requires a veterinary prescription
which will involve a visit to your local vet.
For further details phone: King British Ltd. Mr. Holmes 01274
For more details on commercial preparations phone: Vetrapharm
Ltd. 01425 656081
Top dressing ordinary food
The other option is to apply antibiotic directly to ordinary pelleted
food. This increases the options of which antibiotic can be used. Again,
the antibiotic will have to be obtained via your local veterinary
surgery. The two major problems (once you have calculated the dose) are
getting the antibiotic to bind to the food and not float off when the
pellets are put in the water, and palatability that is making sure
they still taste nice! Tests carried out at the Fish Disease Laboratory
in Weymouth showed either vegetable or fish oils to be the best binding
agents and to have the least affect on palatability.
Preparing the food
Using table 1 calculated the total amount of antibiotic
required. First calculate the total weight of the fish to be
treated. As a rough guide, a 4 fish will weigh 100 grams. 12
fish will weigh approx. 1kg. 18 fish will weigh approx. 2kg.
Determine the total amount of antibiotic required per day. For
example if the total weight of fish was 30kg and you were using
oxytetracycline at a dosage of 75mg/ kg body-weight, you would
need 30 x 75mg = 2.25 grams of active ingredient per day.
On a 14 day course the total amount of active oxytetracycline
required would be 14 x 2.25 grams = 31.5 grams active ingredient (you should be aware
that not all antibiotics are 100% pure).
Calculate the amount of food the fish will eat over a 14-day
period. A good estimate is 1% total body-weight per day. In our
example, 30kg of fish will eat approx. 30kg x 1% x 14 = 4.2 kg
Use a small amount of oil; say 2-3 grams per 100grams of food.
Warm the oil to about 40oC and quickly stir in the
total antibiotic for the 14-day period
Add the oil and drug slurry to all the pellets and stir to
spread the oil slurry evenly over all the pellets. Cool and divide
into 14 equal portions. Store in a sealed container in a cool room
It is sometimes helpful to starve the fish for 24-hours before
starting the treatment
Antibiotics used as
top dressings to treat bacterial disease in ornamental fish
oral: 40-80 mg/kg body-weight daily
oral: 50-100 mg/kg body-weight daily
oral: 30 mg/kg body-weight daily
oral: 10 mg/kg body-weight daily
10 mg/kg body-weight daily
oral:75 mg/kg body-weight daily
Using medicated food is not as effective as antibiotic injections.
Where just a few fish are affected, injections are the best route to
follow. However, where large numbers of fish are affected, or it is not
practical to catch the fish on a repeated basis, then medicated food is
the next best practical treatment method.