FORMALIN AND ITS USE IN AQUACULTURE

Rob McCormack

 

Formalin the active ingredient in Formaldehyde 37/7 is a very common chemical used in the aquaculture industry.  Just recently I had the need to advise a Government Department all I knew on formalin and thought many people might be interested in how I use it or actually write back and let me know the right or better way of using formalin.

I started using formalin some 35 years ago as a preservative.  Formalin is a clear liquid far superior to metholated spirits I was previously using as metho tended to evaporate and discolour.  Glass bottles filled with weird fish, crabs, crayfish, etc and formalin still litter abandoned corners of sheds today.

After bottled specimens, I took the next step up to preserved specimens.  Mostly crustaceans.  This is extremely simple with quite spectacular results.  It is best to use live or freshly killed animals for preserving.  Fill a syringe with formaldehyde and inject it into the joints of the crustacean and into the body.  Not a lot is required for example a 1kg mud crab would take approx 10ml of formalin to preserve the animal.  After injection use a foam box lid to set the crab.  Rest it on the lid, set its legs and claws in the action positions you desire, pins can be used to ensure they stay in place or legs etc can be stabbed into the foam.  Pieces of wood can be used to hold claws up in the air in a threatening position.

Place the lid with the crab on it in a cool dark corner of a unpopulated area and leave for 3 weeks.  Ensure that animals or children do not mess with it.  It will not smell as such, the formaldehyde will dry up and preserve the internals of the animal and set it solidly in your prearranged position.  However, the Formaldehyde it self has a strong odor and is extremely dangerous.  Extreme care must be taken in its use.  For starters ensure you wear cloves to avoid contact with your skin.  Use the chemical outside when there is a breeze to ensure you do not breath it in and make sure you wear goggles.  When you inject yabbies and lobsters, etc. you are forcing this chemical under pressure into your specimen, it is not uncommon for you to remove the syringe and a fountain of chemical to squirt back out.

After 3 weeks or so the specimen is ready for the final touch.  Just use a can of spray varnish to coat and seal the specimen and it is ready for display.  Keep it out of sun light and it will retain its color for a considerable period, but eventually it will fade.  They you need someone with painting skills to touch it up.

My next use of formalin was on crayfish.  Both yabbies and giant spinies and I would use a formalin bath to remove commonsals.  These are small leach like animals (temnocephalans) that crawl over the outside of the crayfish.  In a holding tank approx 6ml of formalin per 100 litres will remove all active commonsals in approx 1 hour.  However it will not remove the eggs usually found on the underside of the crayfish.  I do not use formalin for this anymore, instead approx 20 gram of pool salt per litre for 15-30 minutes does the same job.

My next use of formalin was on my fish.  As a commercial fish hatchery we produce quite a number of fish fingerlings and ectoparasites can be a major problem from time to time.  Ultimately prevention is the best bet.  We heavily lime pond bottoms between crops.  We use hydrated lime at a rate of 500kgs/ha.  This is quite low compared to some recommendations which are up to 3 times this amount but for us we are happy as it does sterilize the pond and kill any leftover parasites from the last crop.

Parasites multiply in poor water quality, so good pond maintenance and regular monitoring help, but even with the best of care parasites can multiply and impact on the health and growth of your fish.

Regular sampling and monitoring of ectoparasite numbers on the fish can be valuable as well as taking the time to observe your fish.  We like to hand feed our fish so we have a intimate relationship with them and can recognize changes in behavior.  We feed half the feed ration into a pond and half to the next and next, etc.  Then back to the first for the second half and then the next, etc.  We can see how our fish are feeding and behaving.  Some typical signs of parasite problems are fish not feeding vigorously or flashing around sides of ponds.  A really bad sign is lethargic fish swimming in the shallows or close to the surface, and the worst is dead fish belly up.

Parasites may not always be the problem so always check oxygen, ph and ammonia first then get a fish under the microscope and check for parasites.

Formalin is one of the chemicals used most commonly around the world for treatment of these typical ectoparasites.  It can be used as a prophylactic treatment to prevent parasite outbreaks or to treat a specific problem.  Most people use formalin as it is relatively cheap, only small amounts are needed, readily available and very effective. 

Currently formalin though widely used in aquaculture in NSW is not registered for use in aquaculture, so is illegal to do so unless under  registered Veterinary prescription, or via a Minor Users Permit (MUP) from the National Registration Authority (NRA) usually taken out by associations to help their members.  In NSW both the NSWAA and SPGA have applied for MUP with the NRA for finfish.  With the formation of Safe Food NSW the use of chemicals in aquaculture is becoming an area of concern for all aquaculturalists.  At this stage AFFA has a verbal confirmation of funding from FRDC to investigate the mechanisms for registration of the common chemicals currently used in aquaculture.  AFFA has their proposal ready for submission now and if successful they will employ a person to investigate the mechanisms and formulate a framework for registration of chemicals for use in aquaculture in Australia.  Formalin is one of these chemicals to be investigated.  Unfortunately this project will take at least a year and then if successful another 12 months before registration for use in aquaculture may occur. 

Formaldehyde Solution 37/7 is a common chemical available from most chemical and aquaculture supply companies and used for a vast variety of applications.  The aquaculture industry uses formalin the active ingredient of formaldehyde to treat a variety of diseases/problems that affect finfish in NSW.

Ectoparasites such as:   C. cyprini

                                      Chilodonella hexasticha

                                      Costia necatrix

                                      Trichodina spp.

                                      Ichthyobodo necator

                                      Ichthyophthirius multifiliis

                                      Tetrahymena sp.

These parasites can all cause serious economic damage to commercial aquaculture facilities if not treated.  The application of 25mg/litre of water will readily and rapidly control outbreaks of these parasites.  It is an economical and effective chemical to utilize.

Fungal diseases such as:  Saprolegnia spp.

                                         Achlya spp.

                                         Aphanomyces piscicida

These fungal diseases also respond to the use of formalin and applications at a rate of 25gm/L are a common treatment, but generally not as effective as some other chemicals. 

Formalin is used in both outside ponds and internal tanks.  Generally the amount required for treatment is diluted at a rate of at least 10:1 and sprayed evenly over the surface of the pond or tank being treated.  It is essential to ensure all aeration devises are fully functional at time of application as deoxygenation of the water can occur.  It is also important to mechanically mix the formalin through the water column.   This can be accomplished by use of paddle wheel aerators or even outboard motors on outside ponds, or just by stirring in internal tanks.

Formaldehyde is a suspected carcinogenic so caution needs to be taken in its application and handling.  Avoid contact with skin and eyes.  Wear protective gloves and goggles.  Avoid fumes, use only in well ventilated areas.  Also be warned that many people are allergic to chemicals and this one is quite common on sensitive peoples list of chemicals to avoid.

Formaldehyde also has the annoying habit of going off.  It should be stored in a safe cool place and used within 24 months of purchase.  When fresh and viable formaldehyde is a clear liquid.  However, when it goes off it becomes milky white and is no longer suitable for use in aquaculture.  In most cases white formaldehyde (Paraformaldehyde) will prove fatal to finfish.  I have heard that you can filter it to remove the white substance but I have never bothered and just thrown it out.  Old chemicals need to be disposed of in a environmentally friendly manner.  Please check with your local council for your nearest chemical disposal depot.

Calculating the amount of formalin needed to treat a pond is always a hassle for me so I have done some base calculations and use those to estimate the amount I need.  Mostly when you see treatment rates of chemicals it is parts per million (ppm) or milligram per litre (mg/L).  1ppm = 1mg/L  and  1gram = 1 ml.

The amount of chemical required = volume of water x dosage rate

For example in a 100 Litre tank treated at 25mg/L

100L x 25mg = 2500mg

2500mg = 2.5gram

2.5g = 2.5ml

Just use an accurate measuring container made from plastic or glass.  I always wear disposable latex gloves as they are cheap and readily available, just buy a box of 100 at any large supermarket.

Calculations become easy after the first time,

500L = 2.5 x 5 = 12.5ml

1000L = 2.5 x 10 = 25ml

A outside pond 50mtr x 20 mtr x 1mtr deep = 50 x20 x1 = 1000 cubic metres.

1cubic metre = 1000 litres

therefore 1,000,000 litres or 1 mega litre would need

1,000,000 L x 25 mg = 25,000,000 mg

25,000,000 mg = 25, 000 gram

25,000gram = 25,000ml    ( 1000ml = 1 Litre)

25,000ml = 25 Litres

For every mega litre of water add 25 litres of formalin.

We have a 380 litre tank which we add 25 litres of formalin too.  We then use a small 1 inch petrol pump to fill the tank with water and mix it with the formalin.  Then use the 1 inch pump to pump out the tank and spray it over and into the pond.  If it is a 3 mega litre pond we just do 3 tanks full.

Well that is it, just food for thought, let me know if you have a better use for formalin or alternative substances to use.

Happy Aquaculture

Robert B McCormack