Fish Parasites 101

August 2005

by Ray Jordan

Fish parasites are fairly common and if detected early and treated successfully they are no bigger deal than fleas or ticks on your dog or cat. Fish parasites can get into your pond by introducing new fish without a proper quarantine period and examination. They can also hitch a ride in on water plants, snails, frogs, and birds. So what would make you suspect your fish might have parasites in the first place? Heavily infested fish will show various signs of stress. They might scrape themselves against the sides or bottom of the pond repeatedly. In serous infestations fish will rub areas on their skin or fins raw and develop skin and fin infections. Sometimes they will just act funny, or suspend at a odd angle in the water. They might even jump out of the water. Sometimes the opposite is true. Fish will lie on the bottom with fins tightly clamped to their bodies. They can either be extra slimy showing a whitish film or almost lacking a slime coat. They can have irritated reddish spots or streaks on their backs, sides, or bellies.

Often for whatever reason one or perhaps just a few of your fish will have the heaviest parasite infestations. However, you still must treat the entire pond. It is just a matter of time until they multiply in large enough numbers to cause infections and affect all your fish. You cannot diagnose which parasite you have by the symptoms. You have to find and identify the type of parasites you have. In some cases there maybe more than one type found. I have seen as many as five types on one microscope slide from a single fish. It is critical to identify that you have fish parasites and treat them specifically and effectively. Shotgun water treatments without knowing what you are treating will delay effective treatment and can also harm your fish and the beneficial bacteria in your filter. In the worse scenario you can kill your fish treating for a parasite you don’t even have.

Let’s start with the most common fish parasites that can be seen without a microscope. Anchor worm and fish lice attach themselves to your fish and by breaking the skin can cause an infection.

Fish lice (Argulus) are actually small crustaceans (see illustration) that will attach themselves to your fish. You will have to look very closely to see fish lice and sometimes what you will notice first are the two black eyespots. Fish lice are about the size of your small fingernail but often are almost clear and blend in with your fishes skin. Place any  fish suspected to have parasites in a plastic bag and look at them very closely. You can use a magnifying glass if you prefer. Look especially closely around the gills and the area just behind and below them. If you see red spots or areas that look irritated look at these areas especially well. You should gently scrape the lice off with your fingernail and then apply a small amount of disinfectant to the area.

Anchor worms (Lernea elegans) attach under a fish scale.(See illustration) When they are quite small you will notice what looks like small red bumps on your fish. If you look closer and perhaps use a magnifying glass you will notice the small worm like projections sticking out of the red bumps. Full size adults are perhaps one half to three fourths of an inch long and are quite easy to see. Just as with fish lice it is best to remove the anchor worms if there are not too numerous. You can use a pair of tweezers to gently pull them off your fish.

The cure for fish lice and anchor worms is easy but the best treatment is hard to obtain. By far the best product is Dimilin. Dimilin is a gyrase inhibitor that is added directly to the pond. It is non toxic to fish and kills fish lice and anchor worms within three to four days. Dimilin is dosed at 1 teaspoon per 1,000 gallons. Dimilin is restricted to commercial aqua cultural use in most areas and just becoming available at retail to hobbyists. Dimilin kills aquatic insects and crustaceans and would be a big problem if it was released into a natural pond environment. It would kill crawfish and other beneficial crustaceans and insects.

Microscopic parasites that are common on koi and goldfish.

FLUKES: The largest common fish parasite requiring a microscope to identify are flukes. These tiny flat worms cannot be seen without a microscope. They are usually easy to find at low power about 40X. In order to see and identify them they much be live motile and swimming around on the slide. Flukes rarely kill fish however they are known to be a major contributor to fish ulcer disease and should be suspected whenever you have an ulcer outbreak.

Flukes are found on the skin of fish as well as around and on their gills. There are two kinds of flukes that affect koi and GF but the same treatments will take care of them all. However one type lays eggs and requires a 2^nd treatment based on water temperature to get rid of all the unhatched flukes. After any parasite treatment you should confirm the absence of parasites with another scraping and microscope exam.

PROTOZOANS: Now we move on to very tiny parasites but despite their size they can be the most deadly to our fish. These tiny parasites will need to be viewed at medium (100X) to high power(400X) with our microscopes. In order to see and identify them they much be live motile and swimming around on the slide. Symptoms in common can include, flashing, jumping, blowing air through gills, hanging out near aeration or siting on bottom with fins clamped to sides. Excess slime to no slime. Red spots or rash and developing ulcers. Eroded irregular gills. Death.  I have placed them in order of the serious threat to the health of your fish.

Ich: Very dangerous parasite and will attack every fish in your pond regardless of health. More common symptoms include sitting on bottom or hovering stationary with fins clamped in head down attitude. It has several life stages and can be difficult to cure. Cannot be treated while embedded in fish tissue. Must be attacked when in free swimming form. Life cycle depends on water treatment and always requires at least three treatments 3 to 6 days apart depending on water temp. Can sometimes see white spots on skin or gills at very advanced stages. Cannot survive in water warmer than 85F.

Costia: Can quickly overwhelm and kill your fish. Costia parasites inject toxins into the gills and skin and starts to digest tissues and allows bacterial infections to begin. Symptoms include excess mucus, resting on bottom, gasping for oxygen, flashing, and heavy mortalities.

Chilodonella: Somewhat less deadly than Ich or Costia. Symptoms include excess mucus, loss of balance, gasping for oxygen, and heavy mortalities. Does not usually result in heavy flashing.

Trichodina: Least deadly of the protozoans. Symptoms are lots of flashing, excess mucus, and bacterial ulcers. Usually found in dirty ponds with high organics.

Treatments: There is no single shotgun treatment for all types of parasites. Because of the different types of parasites you must identify the type or types you have and treat with specific agents. When multiple parasites are present you may need to treat sequentially and with multiple treatments to eradicate them all. After any treatment reexamine fish to be certain all parasites have been eliminated successfully. When multiple parasites are present use treatment that will kill them all if possible or treat most serious first. Then do major water changes and wait 1-2 weeks and treat for less serious parasites until all are eliminated. Read medication labels carefully and carefully calculate and measure all medication used. Be certain of pond volume when treating your pond. Some medications are not safe to run through your filters. Some may be inactivated by carbon or UV sterilizers so discontinue these devices during treatment.

Prevention: Is always the best approach. Quarantine all new fish for a minimum of four weeks at 72-75F. Scrape and examine and if necessary treat all new fish while in quarantine for parasites. Treat all new plants added to you pond with an malachite green/formalin product for at least two weeks before placing in your pond. Design your pond to keep frogs and birds away.

Taking a mucus sample: Use a plastic cover slip to scape some mucus from the koi you are examining. Hold the scraper at a 40 degree angle towards the fishes tail and then gently but firmly scape under the koi’s chin and into the area behind the pec fin towards the tail to obtain a small sample of mucus. It is also important to get a gill scraping by gently holding up the gill cover and scraping some gill tissue and mucus on the slide. Then scrape the mucus onto the glass microscope slide add a drop of pond water and cover with glass cover slip to view under scope. You will not be able to see dead unmoving parasites so you have to have your scope set up pond side and ready to go. Two or three minutes tops and the opportunity to view and identify parasites is over. I suggest scaping each koi in 3 places including the gills and scape at least three koi before you make a determination of what is present.

Using a Microscope: Once the mucus sample is mounted on the slide position it on the scope under the clamps so that the mucus sample is in the viewer. Start with the lowest magnification usually 40X and dim your light source so that you do not “blow out” the sample. While observing the sample form the side lower the objective until it almost touches the cover slip. Look through the eyepiece and use the fine focus adjustment to bring the sample into clear focus. Now we can begin to search the slide for flukes. First look along the cover slip edge where the majority of the mucus sample will be. If it is a gill scraping look closely at the gill fragments as they are prime locations to see flukes. Watch for worm like movements. Cover the entire sample in a grid like fashion looking for flukes. Once you have covered the entire sample at low power switch to medium(100X) power. Now you are looking for protozoans. Start your search again and watch for things swimming around in the mucus on on the gill fragments. You should find areas on the slide where little miniature rivers of water are flowing along. These are perfect places to see parasites being washed out of the mucus. Adjust the lighting as needed to help get the contrast you need to see clearer. After completing the search at medium power switch to high power (400X) and repeat. Once the slide dries out and it will pretty quickly with the hot lamp it is all over. Get another sample. You need to take each sample and then view it with the scope before getting another sample. Believe me the quicker you start viewing the sample the better chance you have of seeing parasites.

Summary & Hints: There are some excellent video clips at this website http://www.fishdoc.co.uk/video/fishmovies.htm and also some terrific protocols for treatment of fish diseases and parasites as well at the main web page which is http://www.fishdoc.co.uk This website is owned by Duncan Griffiths who just published a new book on Step by Step Koi Treatments. The best I have seen so far. There is information on how to order on his website. I strongly urge you to get a copy.

I have purposely spent very little time on treatment in this article. The reason is simple I want you to identify or get someone else to identify the actual parasite or problem with your fish. I have included a fish parasite chart that suggests some treatments. Please consult a expert or a proper fish health book like Duncan’s listed above.

More fish are killed by shotgun treatments for things they don’t have and over dosage than by neglect. If you need assistance in identifying your pond/fish problems please ask someone to help you. If you need specific advise on treating parasite ask a expert.

If you do not have a microscope I suggest you buy one. There are lots of inexpensive used microscopes on ebay or you can buy a used or new one from suppliers like http://www.microscopestore.com/ or call 1-888-255-7267. Good used scopes can be bought for about $100 or a little more.

Most clubs including ours have experienced hobbyists willing and able to help you. TKFGS has two Koi Health Advisors (listed in our newsletters) willing to help you when needed. We have a local fish vet willing to help and you can find his contact information in our newsletter ad section. Also your local pond/fish dealer may be able to provide expert assistance as well.