How to use a microscope
The use of microscopes with koi keeping is becoming more and more accepted as a necessity, and not a luxury, either by owning a microscope yourself or being a member of a club, whereas someone has the knowledge and use of one.
It is not necessary to buy a really expensive microscope to identify each parasite, but in either case it is always a good investment.
1. Lenses - these are the main parts of the microscope, which actually magnify. The eyepiece is the removable top lens, which has a selectable range. The bottom lenses are normally fixed to the microscope, and each one is selected by turning the fixed lens selector. These are fixed to the microscope by threaded ends.
2. Slide fixture - A vernier or spring clips; these actually hold the slide in place under the lens. A vernier holds the slide in place and has an intricate movement control of the slide. The spring clips hold the slide in place once a particular location has been found on the slide, the movement in this case is by hand and requires practise, but once experience has been gained can be quicker than using a vernier.
3. Focus - this is done turning the focus knob, the larger one being for course control, and the smaller one for a fine adjustment. These work by zooming in and out, from the mucus on the slide. This will vary, depending on the lenses used.
4. Light source - this is either a mirror or a light fixed to the microscope. The mirror is tilted and aimed at another light source. A fixed light to a microscope can be mains or battery powered. Either way there is a further control of light via another lens which intensifies the light being passed through the mucus towards the magnification lenses
It is always a good idea to experiment with different small objects placed onto a slide before you attempt a mucus scrape from a koi, following the steps below.
In the top eyepiece you need to put a 5x, and turn the lens selector to a low magnification, around 10x. With these two lenses being used, the magnification will then be 50x, more than enough to overview the slide on first inspection.
Place the slide onto the platform and secure with the spring clamps, or in the vernier arms. Ensure in each case the mucus and cover slip are over the light/lens in a central position.
Look through the eye lens and adjust the lighting first. With low magnification try not to get the light source too bright, this gives a shadow across the mucus sample and is difficult to read for signs of parasites. If you are using a mirror then do not aim the mirror directly at the sun, this can cause damage to the eye. If there is still too much light then adjusting the iris by closing it will cut down the light source. If you have a light on your microscope then again this will help at this stage.
Then use the course-focusing knob to move the lenses closer to the slide until the mucus becomes in focus. The fine adjustment knob will then give you more control in and out to get a better focus.
Further focus and clarity can be gained by moving the light source closer or further away to the slide from the underneath. You will see the balance of light is very important with lower magnification.
Once you are satisfied with the focusing level then I always scan the edge of the mucus first, by going around the outer edge you normally pick up parasites straight away if there is a concern. Once you have scanned the outer edge I scan the slide starting from the top by moving side to side, then by moving down each time until you reach the bottom.
At this magnification most parasites are large enough to be seen, if with your first scan you don't find anything that moves, then do another scan more slowly, by zooming in and out with the fine adjustment- focus. This allows you to look through the layers of mucus, for that final check, to see if any parasites are present trapped in the mucus. If a parasite is found then you can select a higher magnification either by inserting a higher eyepiece lens or by turning the fixed lens selector.
Where koi are related, microscopes cannot identify bacteria, so very high magnification is not needed. Although with these microscopes bacteria can be viewed, it is not possible to determine which bacteria is which like you can with parasites.
If you acquire a microscope kit, which contains Emersion oils and fluids, such as Nigrosin Aqueoues, 1% methylene Blue, these are for further studies and will 'High light' parasites within the mucus, giving colour to the mucus. They are not necessary but can help from time to time.