Quick Answer Trichodina and Costia are both protozoan parasites too small to see with the naked eye, and both are confirmed the same way — a skin or gill scrape examined under a microscope. Trichodina is round, spins like a flying saucer, and is visible at 100x magnification; Costia is far smaller, comma-shaped, and needs

Quick Answer Koi ich (white spot disease) is caused by Ichthyophthirius multifiliis, a protozoan parasite that shows up as tiny white spots — like grains of salt — scattered across the body, fins, and gills. Unlike anchor worm or fish lice, these spots don’t move and aren’t attached structures; they’re the parasite itself embedded in

Quick Answer Koi flukes are microscopic flatworms — Gyrodactylus (skin fluke) and Dactylogyrus (gill fluke) — that are invisible to the naked eye, unlike anchor worm or fish lice. You can’t confirm them by looking; you confirm them by behavior (flashing, clamped fins, gasping at the surface, reduced appetite) and by a skin or gill

Quick Answer Anchor worm (Lernaea) looks like a thin, thread-like white or green filament sticking out of your koi’s skin, while fish lice (Argulus) look like flat, translucent brown discs about 4-10mm wide that move freely across the fish’s body. Both are crustacean parasites, not true worms or insects, and both thrive fastest in water