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This page contains information on Paracide-F for veterinary use.
The information provided typically includes the following:
  • Paracide-F Indications
  • Warnings and cautions for Paracide-F
  • Direction and dosage information for Paracide-F


This treatment applies to the following species:
Manufacturer: Argent

(Formaldehyde Solution)

For Control of External Protozoa and Monogenetic Trematodes on Trout, Salmon, Catfish, Largemouth Bass and Bluegill, and for control of Fungi on Salmon, Trout and Esocid Eggs

NADA 140-831, Approved by FDA

Keep Out of Reach of Children

Active Drug Ingredient

Formalin (aqueous solution of formaldehyde).


Formaldehyde (CH2O)




Water and inert ingredients


Paracide-F Indications

For the control of the following external protozoan parasites, Icthyophthirius spp. (“Ich”), Chilodonella spp., Costia spp., Epistylis spp., Scyphydia spp. and Trichodina spp. and for the monogenic trematodes Cleidodiscus spp., Gyrodactylus spp. and Dactylogyrus spp.


PARACIDE-F is the aqueous solution of formaldehyde gas. U.S.P. grade PARACIDE-F contains not less than 37% (by weight) of formaldehyde gas per weight of water and 6 to 14% methanol. In solution, formaldehyde is present chiefly as HO(CH2O)H. Its molecular weight is 30.93. PARASITE-S is readily miscible with water, methanol, and ethanol and is slightly soluble in ether. It is a clear, colorless liquid (Heyden Newport Chemical Corporation, 1961).

Fish Toxicity Studies

The toxicity of PARACIDE-F was measured by standard methods in laboratory bio-assays with rainbow trout, Atlantic salmon, lake trout, black bullhead, chanel catfish, green sunfish, bluegill, smallmouth bass and largemouth bass. The 3, 6, 24 and 96-hour LC50 (lethal concentration for 50% of the animals) values for trout range from 1,230 to 100 ul/l for catfish, from 495 to 65.8 ul/l; for bluegill, from 2,290 to 100 ul/l; and for largemouth bass, the values to 6 to 96 hours range from 1,030 to 143 ul/l (Bill et al., 1977).

Directions For Use On Trout, Catfish, Largemouth Bass And Bluegill

PARACIDE-F is effective for the control of external parasites on trout, salmon, catfish, largemouth bass and bluegill. Organisms controlled include the protozoa: Ichthyophthirius spp. (“Ich”), Chilodonella spp., Costia spp., Epistylis spp., Scyphydia spp., and Trichodina spp.; monogenic trematodes: Cleidodiscus spp., Gyrodactylus spp., and Dactylogyrus spp.

Concentrations - Concentrations used for treatments are expressed as microliters (ul) of PARACIDE-F (37% formaldehyde) per liter of water and are equivalent to part per million (ppm).

TABLE 1: Concentrations required for control of parasites on the following fish.


Concentration of PARACIDE-F (ul/l)* in

Tanks and raceways
(for up to 1 hour)

Earthen ponds

Salmon and Trout

above 50°F

up to 170


below 50°F

up to 250


Catfish, Largemouth Bass and Bluegill

up to 250


aUse the lower concentrations when pond is heavily loaded with fish or phytoplankton.

*ul/l = microliters per liter.

TABLE 2: Amounts of PARACIDE-F needed to supply effective concentrations in selected volumes of water.

Volume of Water

Amount of PARACIDE-F needed
to give the following concentration of ul/l





10 gallons

0.60 mL

0.95 mL

6.4 mL

9.5 mL

100 liters

1.50 mL

2.50 mL

17.0 mL

25.0 mL

1 acre foot

4.86 gal

8.10 gal



Methods Of Application

Applications to tanks and raceways - Turn off water supply, provide aeration, apply appropriate amount of PARACIDE-F and thoroughly dilute and mix to assure equal distribution of PARACIDE-F. Treat for up to 1 hour, then drain the solution and refill the tank with fresh, well-aerated water. While tank is under treatment, adequate oxygen must be present to maintain the fish. If needed, aeration should be provided to prevent oxygen depletion. Treatments may be repeated daily until parasite control is achieved.

Application to ponds - Apply greatly diluted PARACIDE-F to the pond evenly using a pump, sprayer, boat bailer, or other suitable device to assure even distribution. Allow PARACIDE-F to dissipate naturally. Single treatments usually control most parasites but may be repeated in 5 to 10 days if needed. Treatments of Ichthyophthirius should be made at 2-day intervals until control is achieved.

Use For Directions For Trout, Salmon And Escoid Eggs

PARACIDE-F is effective for the control of fungi (Saprolegniaceae family) on eggs of salmonids and esocids.

Concentrations - Apply concentration of 1,000 to 2,000 ul/l (3.8 to 7.6 mL/gallon of water). The most widely used concentration is about 1,670 ul/l.

Method of application: Apply as constant flow to water supply of incubating facilities for 15 minutes. Repeat treatment as often as necessary to control growth of fungi.


Harmful if inhaled or absorbed through the skin. Do not get in eyes or on skin. If PARACIDE-F is inhaled, remove the patient to fresh air. Irritation may be alleviated by inhalation of spirits of ammonia. If eyes or skin are exposed to PARACIDE-F, wash with water. Eyes should be flushed freely with water for at least 15 minutes and then treated by a physician.

Harmful if swallowed. PARACIDE-F should be diluted and removed from the stomach as rapidly as possible. Irritation may then be alleviated with demulcents.

Paracide-F Caution

1. Do not use PARACIDE-F which has been subjected to temperatures lower than 40°F or allowed to freeze. Cold or freezing causes the formation of paraformaldehyde, a substance which is toxic to fish. Paraformaldehyde can be recognized as a white precipitate at the bottom or on the walls of the container.

2. DO NOT USE ON STRIPED BASS (Morone saxatillis). Tolerances to PARACIDE-F may vary with strains and species of fish. While the indicated concentrations are considered safe for the indicated fishes, a small number of each lot to be treated should be used to check for any unusual sensitivity to PARACIDE-F before processing. Striped bass (Morone saxatillis) are known to be highly sensitive to PARACIDE-F so pond treatments are not appropriate for this species.

3. Under some conditions, fish may be stressed by normal treatment concentrations. Heavily parasitized or diseased fish often have a greatly reduced tolerance to PARACIDE-F. Such fish do not tolerate the normal tank treatment regimen the first day they are treated. Therefore the time or dosage or both may need to be reduced if the fish show evidence of distress (by piping at the surface). The solution should be removed and replaced with fresh, well-aerated water. Careful observations should always be made throughout the treatment period whenever tank or raceway treatments are made. Treatments in tanks should never exceed 1 hour even if the fish show no signs of stress.

4. Do not apply PARACIDE-F to ponds with water warmer than 27°C (80°F) when a heavy bloom of phytoplankton is present or when the concentration of dissolved oxygen is less than 5 mg/L (5 ppm). PARACIDE-F may kill phytoplankton and can cause depletion of dissolved oxygen. If an oxygen depletion occurs, add fresh, well-aerated water to dilute the solution and to provide oxygen.

5. Do not discharge the contents of fish treatment tanks into natural streams or ponds without thorough dilution (greater than or equal to 10%). Do not discharge the contents of egg treatment tanks without a 75% dilution. This will avoid damage to PARACIDE-F sensitive phytoplankton, zooplankton, and fish populations and avoid depletion of dissolved oxygen.

6. Do not use PARACIDE-F in a tank or pond in which methylene blue or other dyes have been recently used.

ORM-A UN 2209

NDC 051212-0016-2

Manufactured For Argent Chemical Laboratories, Inc., Redmond, WA 98052

ARGENT Chemical Laboratories, 8702 152nd Ave. N.E., Redmond, Washington U.S.A. 98052

Net Contents: 4 x 1 gallon (U.S.) cases, 5 gallon container and 55 gallon drum.

NAC No.: 10260011

8702-152ND AVENUE N.E., REDMOND, WA, 98052
Telephone:   425-885-3777
Order Desk:   800-426-6258
Fax:   425-885-2112
Every effort has been made to ensure the accuracy of the Paracide-F information published above. However, it remains the responsibility of the readers to familiarize themselves with the product information contained on the US product label or package insert.

Copyright © 2018 North American Compendiums. Updated: 2018-03-29