Diagnosis: Microscopic Examination (Part 3)

In In part 2, we stated that pond fish, and cyprinids in particular, thrive best at a stable pH between 7 and 8. Pond fish do not tolerate pH that is too low, too high, or fluctuating significantly.

Speed

Examine your specimen within five to ten minutes of collecting the mucous membrane, gill fragment, or fresh feces. Parasites quickly become less active once removed from the host and die off quickly. Therefore, work efficiently but certainly not hastily. For example, don't catch and scrape three fish before starting the microscopic examination; instead, perform all steps for each fish in sequence.

Magnification

Place the slide on the microscope stage and set the microscope to 100x magnification (10x eyepiece and 10x objective). Some hobbyists prefer to start with 40x magnification for a quick initial scan. After examining the slide at 100x, rotate the turret to 20x objective and examine your slide again at 200x magnification. This allows you to see even the tiniest, recognizable parasites.

Research method

Make sure the objective lens is set approximately to the center of your slide. Turn the coarse focus screw until you have a reasonable image. Then, turn the cross-stage adjustment screws and locate a corner of your coverslip. This is the starting point of your examination. Adjust the focus with the fine focus screw. Now use the cross-stage adjustment screws to systematically examine your slide.

Make a zigzagging motion over the specimen, paying particular attention to the transition between the mucous membrane and the surrounding water. Use the fine-focusing screw to focus your image each time you move over the specimen. This is necessary because you're looking at a three-dimensional mucous membrane, so the focus point will always be slightly different. Any movement you see is suspicious (potential parasite)!

Important !

Focus primarily on smaller parasites like Costia. These are often missed, especially when other parasites are also present. You might think you've found the problem, but you're missing part of it.

Author: Joop van Tol (www.koitoday.nl)