In this article and video we will explain and demonstrate how to take a skin scrape from a small aquarium fish, because sometimes it is necessary to look for microscopic parasites on the skin of fish. Depending on the size and species of fish, the procedure is slightly different. For small aquarium fish, we can do a skin scraping with a cover glass or scalpel to create a slide for microscopic examination.
What you need
To perform a skin scrape, we need the following tools and objects:
- A container with a lid to hold the fish temporarily
- Fish net
- Standard sized microscope slides
- Cover glasses
- A pipette or syringe
- Paper tissues
- A well-lit workstation
Let’s look at the steps we need to follow:
1. Rinse the container with aquarium water and fill it with enough water to cover the fish.
2. Catch the fish with the net and place it inside the container. Put a cover on top to prevent the fish from accidentally jumping out.
3. Most fish will be agitated at first, but calm down quickly. Sometimes it may be necessary to use a light sedative.
4. Place the slide on a tissue or towel to prevent water from getting in between the glass and the table.
There are several different ways and various tools we can use to do the skin scraping. For this small sized fish I prefer to use a cover glass, but for larger fish we use a slide.
5. Carefully remove the fish from the container. This can also be done with a net.
6. Hold the fish, so that it can be scraped from head to tail, depending on whether you are left- or right-handed.
7. Hold the cover glass, or other tool, at a 45-degree angle. Now gently, without pressing hard, move the slide along the body of the fish from head to tail.
TIP: If you use the same pressure as when writing with a pencil, you will not hurt the fish. A sample of slime and perhaps a few scales will be left on the glass.
8. Release the fish back into the container and put a cover on it.
9. Use a pipette to put a drop of aquarium water onto the middle of the slide. Use the cover glass to mix the mucus and the water on the slide.
10. Then place the cover glass on the slide. If you get many air bubbles, use a needle or tweezers to carefully release the cover glass.
11. Pressing gently with the tweezers, distribute the smear between the cover glass and the slide.
12. The specimen is now ready for microscopic examination.
It is important to examine this specimen within five minutes after the scraping because we will be looking for moving parasites under the microscope and some parasites will stop moving after about 5 minutes. The main parasites you can find with a skin scrape are skin and gill flukes, Costia or Ichthyobodo necatrix, Trichodina, Ichthyophthirius, Tetrahymena, Chilodonella, Oodinium and Flavobacterium columnaris.
Good luck! If you have any questions, don’t hesitate to contact us.