Skip to Content

Parasite-S (Canada)

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


This treatment applies to the following species:
Company: Syndel



Formaldehyde (CH2O)

37% w/v



6 - 14% w/v

Water and inert ingredients

49 - 57% w/v

Read Entire Package Insert Before Using This Product

(Formaldehyde solution 37%)

For control of External Protozoa and Monogenetic Trematodes on Salmonid Fish and for Control of Fungi on the eggs of Salmonid Fish.



Formalin has been used since 1909 in the United States in the production of sport, commercial, and experimental fishes (Schnick 1973). It is used as a therapeutant and prophylactic for the control of external parasites on salmon, trout, catfish, largemouth bass, and bluegill, and for the control of fungi on salmon, trout, and esocid eggs. PARASITE-S has been used since the early 1970’s to control external protozoans on penaeid shrimp (Johnson et al. 1973).


PARASITE-S is the aqueous solution of formaldehyde gas. U.S.P. grade PARASITE-S contains no 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).

Parasite-S Indications On Salmonid Fish

PARASITE-S is effective for the control of external parasites on Salmonid fish. Organisms controlled include the protozoa; Ichthyophthirius spp., (“Ich”), Chilodonella spp., Ichthyobodo spp., Ambiphrya spp., Epistylis spp., and Trichodina spp., and for the monogenetic trematodes: Cleidodiscus spp., Gyrodactylus spp., and Dactylogyrus spp.

Parasite-S Indications For Salmonid Eggs

PARASITE-S is effective for the control of fungi (Saprolegniaceae) on eggs of salmonid fish.

Parasite-S Dosage And Administration For Fish

CONCENTRATIONS - Concentrations used for treatment are expressed as microliter (µL) of formalin (37% formaldehyde) per liter of water and are equivalent to parts per million (ppm).

Table 1. Concentrations required for control of parasites on fish.


Concentration of Formalin (µ/L*) in

Tanks and raceway (for up to 1 hour)

Earthen ponds (indefinitely)

Salmonid Fish
above 50°F
below 50°F

up to 170 (62.9)
up to 250 (92.5)

15-25 (5.55-9.25)
15-25 (5.55-9.25)

Use the lower concentrations when pond is heavily loaded with fish, shrimp or phytoplankton.

* µL/L = microliters per liter (ppm)

The figure in the parenthesis denotes the concentration of formaldehyde expressed as parts per million (ppm) by weight.

A single treatment usually controls most parasites but may be repeated in 5 to 10 days, if needed.

Table 2. Amounts of PARASITE-S needed to supply effective concentrations in selected volumes of water.

Volume of water

Amount of PARASITE-S needed to give the following concentration of µL/L





100 liters

1.50 ml

2.50 ml

17.0 ml

25.0 ml

Methods Of Application

APPLICATION TO TANKS AND RACEWAYS - Turn off water supply, provide aeration, apply appropriate amount of PARASITE-S, and thoroughly dilute and mix to ensure equal distribution of PARASITE-S. Treat for up to 1 hour for fish, 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 or shrimp. 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 PARASITE-S to the pond evenly using a pump, sprayer, boat bailer, or other suitable device to ensure even distribution. Allow PARASITE-S to dissipate naturally. Single treatments usually control most parasites but may be repeated in 5 to 10 days if needed. Treatments for Ichthyophthirius should be made at 2-day intervals until control is achieved.


CONCENTRATIONS - Apply concentration of 1,000 to 2,000 µL/L. The most widely used concentration is approx. 1,670 µL/L (618 ppm formaldehyde).

METHOD OF APPLICATION - Apply as constant flow to water supply of incubating facilities for 15 minutes. Repeat treatment as often as necessary to prevent growth of fungi.

Parasite-S Cautions

Store PARASITE-S indoors away from direct sunlight, heat, sparks, and open flames, and ventilate storage area. Do not subject PARASITE-S to temperatures below 4.4°C (40°F). PARASITE-S subjected to temperatures below 4.4°C (40°F) 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.

Tolerance to PARASITE-S may vary with strain 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 PARASITE-S before proceeding.

Under some conditions, fish may be stressed by normal treatment concentrations. Heavily parasitized or diseased fish often have a greatly reduced tolerance to PARASITE-S. Such animals do not tolerate the normal tank treatment regimen the first time they are treated. Therefore, time or dosage or both may need to be reduced. If 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. Treatment in tanks should never exceed 1 hour for fish even if the fish show no sign of distress.

Do not apply PARASITE-S 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). PARASITE-S 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.

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

Do not use PARASITE-S in a tank or pond in which methylene blue, or other dyes, which are absorbed, have been recently used.


Keep out of reach of children.

Hazardous Ingredients

The ingredients listed below have been associated with one or more of the listed immediate and/or delayed (*) health hazards. Risk of damage and effects depends upon duration and level of exposure. BEFORE USING OR HANDLING, READ AND UNDERSTAND THE SDS.


67-56-1 *METHANOL



Immediate Health Hazards

SKIN ABSORPTION: May be harmful if absorbed through skin.

INGESTION: May be harmful if swallowed.

If accidently swallowed, burns or irritation to mucous membranes, esophagus or GI tract can result. Can cause central nervous system depression.

INHALATION: May be harmful if inhaled. Liquid or vapour may cause irritation of nose, throat and lungs.

Can cause central nervous system depression.

SKIN: Causes irritation.

EYES: Causes chemical burns.

Handling Precautions

Formaldehyde vapour may be carcinogenic if inhaled. Use applicable safety protection such as wearing personal protective equipment. Wash thoroughly after handling.

INHALATION: Avoid breathing vapor. Use with adequate ventilation.

SKIN: Avoid contact with skin and personal clothing.

EYES: Do not get in eyes.

First Aid

SKIN ABSORPTION: In case of contact, immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Wash clothing and shoes before reuse.

INGESTION: If accidently swallowed, dilute by drinking large quantities of water. Immediately contact poison control center or hospital emergency room for any other additional treatment directions.

INHALATION: If inhaled, remove to fresh air. If not breathing, give artificial respiration, preferably mouth-to-mouth. Call a physician.

SKIN CONTACT: Flush skin with plenty of water. Remove contaminated clothing. Call a physician if irritation persists.

EYE CONTACT: Immediately flush eyes with plenty of water for at least 15 minutes. Eyelids should be held apart during irrigation to ensure water contact with entire surface of eyes and lids. Call a physician.

Fish Toxicity Studies

The toxicity of PARASITE-S was measured by standard methods in laboratory bio-assays with rainbow trout, Atlantic salmon and lake trout. The 3, 6, 24 and 96-hour LC50 (lethal concentration to 50% of the animals) values for trout range from 1230 to 100 µL/L (455 to 37 ppm formaldehyde).


KEEP CONTENTS FROM FREEZING. Recommended storage temperature 15°C (59°F). DO NOT EXPOSE TO DIRECT SUNLIGHT. Store PARASITE-S indoors away from direct sunlight, heat, spark, and open flame, and ventilate storage area. Do not subject PARASITE-S to temperature below 4.4°C (40°F).




Manufactured for: Syndel CANADA, 9-4131 Mostar Road, Nanaimo, B.C. V9S 4M9

250-585-2006 or 1-800-663-2282

ver. 110719

DIN: 02118114


Net Contents 208.2 Litres [55 (U.S.) GALLONS], 1000 Litres [263.8 (U.S.) GALLONS]

CPN: 1244007.1

#9&10, 4131 MOSTAR ROAD, NANAIMO, BC, V9T 6A6
Telephone:   250-585-2006
Technical Service:   250-585-2006
Order Desk:   800-663-2282
Toll-Free:   800-663-2282
Fax:   250-585-5300
Every effort has been made to ensure the accuracy of the Parasite-S information published above. However, it remains the responsibility of the readers to familiarize themselves with the product information contained on the Canadian product label or package insert.

Copyright © 2021 Animalytix LLC. Updated: 2020-12-31