Hydra in aquarium: what they are and how to remove them

Hydra are tiny freshwater animals related to jellyfish — small translucent stalks with a ring of stinging tentacles. They hitchhike into tanks on live plants, decor, or new livestock and attach to glass, plants, or substrate. They catch tiny prey with their tentacles and can reproduce quickly by budding.

For adult fish, hydra are usually harmless; the stings are too weak to penetrate skin. The real risk is to fry and very small shrimp, which can be stung and killed. If you’re raising fry or keeping dwarf shrimp with babies, hydra can be a problem. In a community tank with only adult fish, many keepers leave them or remove them for aesthetics.

Our full guide to hydra covers removal options (manual removal, Fenbendazole, No Planaria, reducing food), the snail warning with Fenbendazole, and prevention with plant dips and quarantine. See also mystery snails, quarantine, and overfeeding.