Parasites, How do you know if your fish has them

By James P. Reilly

Parasites on fish are like fleas on a dog. And when your dog has fleas what does he do? He scratches! And so do your koi! Only with no paws it requires greater imagination! In the hobby we call it flashing. A koi will look around for a ‘handy surface’, move over to it and then in a flash, dash its body along the protruding surface. In a mud pond, flashing in the mud can dislodge an annoying parasite with little or no harm. But in our ponds, this flashing action can do secondary damage to a koi if the object is a rock, an air dome bottom drain or return pipe edge/opening. In fact, the whole dynamic of aeromonas bacterial infection is begun when the protective slime coat and the natural immune agents it contains, is breached and the bare epidermis is exposed to opportunistic bacteria. Flashing is one mechanical activity that damages skin and allows for infection. For this reason, serious koi show hobbyists design their pond very carefully so that no angles, stone edges or protrusions of any kind exist in their ponds.
\r\nStill, koi will do what they do and flashing is a normal groom activity in health koi.

So what is a hobbyist to do?
\r\nWell, one of the most enjoyable parts of the hobby is watching your fish! And this is the ideal time to monitor your fish’s general health. It is during this time that you might begin to see the flashing behavior. Take note of who flashes and how often you see this behavior. Is it one fish or all the fish? Is it casual or is it frantic and obsessive? Are the koi ‘chewing’ yet you have not fed them? Are they shaking their heads ? Are they jumping out of the water and crashing on the surface ( another technique like flashing to dislodge offending parasites).
\r\nWhat action should a hobbyist take?
\r\nWell first of all, Don’t panic! First test your water. You want to make sure there is no ammonia and that your pH has not shifted. Has it rained recently? Rain will change pH. Has anyone sprayed yard chemicals ? Have you recently done a water change? Do you use a carbon or resin filter on your tap water outlet? ( it’s a good idea). If these tests all read normal and no rain or roof run off or sprays are a possibility then move to step 2-

Step 2: you need to net some of the fish that are flashing and have a fellow koi club member help you take a sample of the fish’s slime coat to examine under a microscope. Its really very easy once you do it a time or two. You will need :
\r\n* a microscope ( nothing fancy just a basic microscope)
\r\n* a box of microscope glass slides
\r\n* a box of plastic lens covers.

Parasites tend to congregate on certain areas on the body based on the species. Universal areas for all parasites tend to be along the side of the body, on and along the shoulder, in the pec areas, top of the head and the tail tube area. So you want to run the plastic cover slip edge or the glass slide itself ( edge) over the fish’s body as if you were ‘shaving’ the fish. You want to ‘shave’ an inch or so of surface. This will collect a thin layer of slime coat and trap the parasites within that mucous sample.
\r\nNow take the cover slip or slide and transfer/spread the slime sample across the glass slide. Add a drop of water and a new cover slip and you are ready to examine the slide under the scope.
\r\nAfter placing the slide on the stage of the microscope, adjust the light so that you can see the details of the sample. DO NOT have the light too bright as the parasites are thin walled creatures and the bright light will burn right though the transparent protozoa and make then invisible to your eyes. After a short while you will get good at this. It’s not a bad idea to order a few premount slides of micro organisms when you order your slides from the mail order company ( Carolina biological supply is a good one) . This way you can get some practice before you try the real thing.
\r\nOf all the parasites in the world, you will only really be interested in identifying about six species. They are skin and gill flukes, Ich, Costia, Chilodonella and Trichodina. The other two common offenders are actually visible without the need for the microscope and they are , lernaea or anchor worms and Argulus or fish lice. There are others, both microscopic and macro, but in the vast majority of cases, you will be dealing with just the six ‘minies’ I mentioned. I’d recommend the reader get a copy of Dr Nicholas Saint-Erne DVM’s book Advanced Ki Care for Veterinarians and Professional Koi Keepers , for better identification of these parasites.