Biopsy of Koi, goldfish and pond fish

Knowing how to use a microscope is one thing, but having the specimens to look at is equally important. More importantly, having “good” or viable specimens is paramount. So let’s look at the “How To” of biopsy collection from Koi, goldfish and pond fish.

The equipment needed is relatively easy. A box of ‘slides’ <graphic> represents an investment of about seven dollars depending upon where you get them. I mentioned several resources and will again in the “Further Resources” section of this book. A box of coverslips is also affordable and there are about a hundred slips in a box. Plastic coverslips are infinitely preferable because they do not break under stress.

You would simply use a coverslip and gently scrape up a bit of mucus. The mucus drop should adhere to the coverslip. You would place a drop of uncontaminated aquarium water on the slide and then place the coverslip <graphic> with its drop of mucus onto the drop of water. A seal will form between the coverslip and the slide.

This is your “specimen” or preparation. The appearance of ‘normal’ mucus and the usual bubbles is depicted in the section on using the microscope.

Let’s consider the clinical relevance of the parasites you discover under the microscope. Here are some basic points to start with. Your experience will eventually be your guide.

Any parasite you see is a potential threat to the Koi, goldfish and pond fish.

When you see a lot of parasites under the microscope (ten or more per low power field) and you’re seeing ‘sick’ fish, you should infer a clinical relationship and design a treatment protocol to eliminate the parasite.

On the other hand, sometimes you find a parasite when you are doing a routine biopsy on a Koi, goldfish and pond fish and there are no clinically affected fish. You should pause and ask yourself if ‘right now’ is the best time to treat, (sometimes it isn’t) and choose a treatment that will not make otherwise healthy fish unhealthy.

Sometimes you find something which is not in the classic textbooks of fish disease. Chances are, it’s a stray, non-pathogenic organism. Strive to learn the “big names” in the parasite business (the real killers) and when you encounter something unfamiliar or uncommon, try and relax.

Clinically relevant points worth mentioning include the advice to keep your specimens fresh. I mentioned in the section on Chilodonella that this parasite is extremely fragile under biopsy conditions and will die very shortly after collection. Costia is another parasite that perishes relatively quickly. Costia is so small that its diagnosis is almost dependent upon seeing their motion at lower powers.