Threat level: Moderate
Hydra are anemones that can be found in freshwater aquariums. They are tubular in shape with long tentacles that contain small, bumpy areas called cnidocytes (nye-do-sites) which are stinging cells that inject neurotoxins into their prey. The green coloration of hydra stems from its ability to have a symbiotic relationship with a small dinoflagellate algae known as Chlorella. It swallows the algae and becomes its host. From there, it harnesses the algae’s ability to photosynthesize in order to make nutrients.
However, hydras are also carnivorous. They can capture tiny crustaceans, aquatic worms, shrimp, and even small fish and fry. If food is in abundance, they can be a general nuisance to any aquarium hobbyist who wants to breed shrimp and fish.
For more information or general methods of controlling hydra, watch my latest video and I will show you how I combated these amazing, but annoying, pests in my own aquariums.