Practical fish-health skills
How a koi skin-mucus scrape is taken
A skin scrape collects a small mucus sample for a fresh microscope examination. It is not a viral test, and it should not remove scales.
1. Prepare before catching the fish
Have a trained keeper or fish-health professional demonstrate handling first. Set out a clean slide, coverslip, microscope, fish-safe sampling edge and suitable wet handling equipment. Work beside a secure bowl so a struggling fish cannot fall. Do not start with a fish in breathing distress; call for help.
2. Collect mucus gently
With the fish safely supported and kept wet, the trained sampler makes a light pass along the skin from head towards tail using the edge of a coverslip or suitable sampling tool. The aim is a small amount of mucus, not a wound. Avoid eyes, gills, the lateral line and damaged tissue. Stop if the fish struggles or tissue is injured.
3. Make a fresh wet mount
Place the mucus on a clean slide with a small drop of suitable system water, then lower a coverslip gently. Keep the sample thin enough to examine. Label the fish and sample location. Return the fish safely to suitable water promptly, then examine the fresh sample without delay.
4. Examine systematically
Begin at low power to find the sample, then increase magnification as needed. Scan in an orderly pattern rather than staring at one spot. Record the objective and eyepiece used, sample site and what was seen. Ask an experienced examiner to confirm unfamiliar organisms.
5. Know when the scrape is not enough
No parasites seen means none were seen in that sample. Persistent symptoms may require better samples, a gill assessment, culture or viral testing. Gill clips, sedation and invasive sampling belong with appropriately trained professionals; this guide does not teach those procedures.
Sources & further reading
Original WakeyKoi wording, informed by the references below. Linked clinical resources explain the evidence and their scope; they have not reviewed or endorsed this website.
Related guides
Educational guidance cannot diagnose an individual fish. Breathing distress, severe injury or unexplained losses need prompt professional assessment.