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FORMALIN
Formaldehyde sol. 37% vol.
EXTERNALLY APPLIED
ANTI-MICROBIAL & ANTI-PARASITIC AGENT
Description:
Formalin is a colourless
transparent liquid with characteristic sharp odour and specific gravity
1.09kg/lt. (20°C).
It is a virtually saturated solution of
formaldehyde in water. At normal water temperatures it contains 34-38% w/w
formaldehyde. Usually, it contains 12% methanol to slow down the polymerisation
of the formaldehyde.
Indications:
Formalin is a widely used
anti-parasitic agent, effective against many protozoa and monogenetic fluke
parasites of fish skin and gills. It is also active against many bacteria, such
as the Gram negative filamentous bacteria infecting the fish gills. Formalin is
safe even for small fish when used in baths according to proper protocols.
Apart from its
therapeutic use, formalin is used also for prophylaxis against the
ecto-parasites in order to prevent the seasonal build up of parasitic loads on
caged fish, or the proliferation of the parasites on valuable brood fish in
hatcheries.
Formalin dilutions may be used as a strong disinfectant in hatcheries.
Administration:
It is recommended that a
light dilution of formalin (1:100) is prepared and gradually dispersed in the
fish tank or tarpaulin until the required bath concentration is achieved.
Diluted Ο2 should remain at the safe levels of
6 to 8ppm.
Formalin baths should last up to 60 minutes and may be repeated
according to veterinary instructions, depending on the season and the type of
parasitic infestation under treatment. Formalin baths are not
recommended when the water temperature exceeds 26°C.
Diluted solutions are
normally designated by their content of formalin, not of formaldehyde; for
example a use concentration obtained by diluting formalin 1:10,000 will be
designated 0.01% formalin or 100ppm formalin but actually contains about 37μg/ml (ppm) formaldehyde.
The maximum safe formalin
concentrations in baths differ according to the age/size of the fish and the
level of dissolved oxygen in the water. Formalin is a reducing agent, which
will absorb oxygen from water; in addition it irritates the gills and lowers
the efficiency of osmoregulation and gaseous exchange at the gill epithelium. Besides, when
formalin baths are applied, the bacteria and/or the parasites, which the baths
are meant to destroy, have already impaired the gill function. Therefore, water
aeration, or preferably water oxygenation, should be provided throughout a
formalin bath.
Indicative
formalin concentrations for hourly baths (sea bream and sea bass):
·
Fry 0.3g-0.5g: 30ppm · Fry 0.5g-1.5g: 50ppm · Fingerlings 1.5g-3g: 80ppm
· Fingerlings 3g-20g: 120ppm · Caged fish >20g: 150ppm · Brood-stock: 200ppm.
Precautions
(for operator safety):
Undiluted formalin is toxic and
caustic for the skin and eyes as well as for the upper respiratory tract when
fumes are inhaled and the gastrointestinal tract if accidentally swallowed. In
the eyes formalin is very irritant, even in considerable dilution. Always flush
exposed eyes or skin with plenty clean water for several minutes. If
accidentally swallowed, the patient should drink plenty of water, vomiting
should be induced and demulcents taken. Subsequent to such first aid measures
proper medical advice should be sought after.
When handling
formalin apply safety measures and use proper equipment. Keep away from children.
Packaging
and storage:
Formalin is distributed in sealed plastic
containers of 27kg (24.8 lt.), most often 30kg (27.5 lt.) and up to 35kg (32.1
lt.).
It should be stored in a ventilated, dark place, away from oxidising
agents. Storage temperature should exceed 10°C. (Polymerisation of
formaldehyde to the toxic polymer, paraldehyde, occurs faster in sunlight and
at low temperatures.)
Disclaimer:
Every effort has been made to ensure that the information above is
accurate until the date of last editing. It is based upon the accumulated experience
of applied veterinary work. The information may be used as a guide and is not
meant to replace professional veterinary guidance for disease treatment.
The author cannot take responsibility for incorrect interpretation or any
resulting consequences.
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Copyright (c) Dr Panos Varvarigos