Ectoparasites refers to all parasites that infest fish from the outside. The symptoms may be similar (rubbing, film on the skin, etc.), even though the pathogens are completely different. If ectoparasites are suspected, further distinction is very helpful. However, this requires a good magnifying glass or even a microscope. With a magnification of only 100 – 200 times, most ectoparasites can be identified quickly, even with little experience.