microscopes for koi

A Microscope for Use in the Koi Hobby

[reprinted from our 2004 Catalogue]
You wander outside one warm day to feed your fish. Alarmingly, you notice several fish flashing against the sides of the pond, as if they were scratching an itch. The reality is that they are. Once you eliminate water quality as the source of the problem, you need to ask yourself is the flashing a result of Flukes or perhaps another parasite? The preferred treatment for Flukes, Prazzi pond, does nothing to eradicate Protozoa. Proform-c, great for ridding koi of Protozoa and flukes, does nothing to kill fish lice. Obviously without an accurate diagnosis of the affliction, how do you effectively proceed ? The fact is you can't, not without your trusted microscope

We all used microscopes in high school, likely not realizing then that they could provide invaluable information to us in our future as Koi hobbyists. Daunting to some, the reality of doing scrapes is that it is quite simple and easily mastered. A basic microscope is all that is required, a “high dry” resolving power of 400x will more than suffice. This will allow you to make an accurate assessment of what pests [with the exception of bacteria] are afflicting your Koi. With this information you are able to best decide what treatment regimen to employ to cure your fish


A basic microscope will cost about $200.00 - less than the price of a decent grade koi. A power of 400x is recommended and the microscope should have a light bulb, not a mirror, as its source of illumination. The ocular lens, or eyepiece you look in, will likely have a fixed power of 10x. The rotating subjective lenses will likely be powered at 4x, 10x and 40x. This provides magnification powers of 40x, 100x and 400x

Larger parasites, such as the nasty aforementioned Flukes, are readily visible at 40x. A little practice is required mastering the movement of the mechanical stage if your scope has one. With less expensive scopes, you have to move the slide by hand. A common mistake often made is to over illuminate the slide - so start off at a lower light power and a resolving power of 40x for your initial examination. The best image is one of contrast is what my microbiology teacher told us

The scraping off of a mucous sample from the fish can be a little daunting to some. I personally use the slide but you can also use a popsicle stick if you like. I have seen the cover slip used and frankly I think that is a mistake. Perform your scrape gently but firmly on the suspect fish. Good locations are at the bases of the pectoral fins, the peduncle, below the dorsal fin, the belly etc. Of course, wounds are also good spots. Very little mucous is required. I use the cover slip to arrange the mucous in the middle of the slide. I then add a drop of pond water and put the cover slip over the sample for examination with the scope

It is important to move with a purpose, if the sample contains parasites they may stop moving fairly quickly on the slide making spotting them more difficult. Although I have seen movement 20+ minutes later, you should spend at least 2-3 minutes on 40, 100 and 400x resolving powers. I have the microscope with me, right by the pond, setup and ready to go before I do the scrape. Remember don't quit when you find something, there could be more parasites that may not share the cure

Inspecting the slide is fun and one quickly realizes that there is a whole other miniature world living amongst us. Most of the parasites look like something out of the Aliens movies and I still even cringe at times. Start at 40x and slowly pan around the slide. Experience will allow you to quickly discard air bubbles and moving currents of water as potential pathogens. When I first started using the microscope it took awhile for me to actually find anything. I wasn't sure whether it was my inexperience or that the fish were clean

It is recommended to scrape in at l=least 2 if not 3 scrapes locations on a single fish to determine conclusively if it is clean or not. Scraping several fish is also advisable before a clean bill of health can be given to a given system. When you do discover something wiggling on the slide you will be excited but yet concerned at the same time. How many parasites are too many ? Flukes are very common. If you find only 1-2 on 3 good scrapes, you do not really have a fluke problem in the pond. Healthy fish can deal with these. If you find several on 1 slide, and of different sizes, then a quick treatment response is advisable. When you start finding 4 or more flukes, treatment is advised. A serious infestation would be 20+ flukes on a single field of view at 40x and this is a nasty sight

The reality is that fish will always carry some parasites, it’s when they are weak that a population explosion occurs and the Koi hobbyist has to take quick action. Knowing the enemies lifecycle as it pertains to temperature is also imperative. Most parasites have lifecycles under 30 days in “Summer temperatures”. It took me a long time to get around to buying a microscope. But like many other tools, once you have one, you wonder how you did without. I have also just finished taking a Microbiology course [2004] which has covered both practical and theoretical aspects of maximizing the benefit of this most useful tool. Thank you Anthony Von Leeuwenhoek !