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Hydra: The Tiny Threat in Your Aquarium

Updated: Jul 18, 2023

If you have aquariums, you've likely heard of a variety of little pests that can supposedly wreak havoc on your beloved aquatic paradises.

In this blog, we'll focus on Hydra - a small, freshwater organism belonging to phylum Cnidaria, making Hydra most similar to jellyfish, coral, and anemones. Hydra is an interesting organism, but it can also be a threat to your aquarium and its inhabitants.

Where Does Hydra Come From?

Hydra is found all over the world, in both freshwater and saltwater environments. In aquariums, Hydra can be introduced through live food, live plants, or even on the equipment that you use in your aquarium.Hydra thrives in freshwater environments with stable water conditions, adequate food, and oxygen (the very same conditions we all strive to achieve for our fish!).


Hydra can reproduce quickly under these favorable conditions, with a single Hydra capable of producing up to 25 offspring a day. However, they can also survive under adverse conditions by retracting their tentacles and forming a protective capsule around their body. This makes them quite hardy, allowing them to to wait out unfavorable conditions until water conditions improve.

Potential Negative Effects of Hydra on Aquariums and Inhabitants

Hydra can prey on small fish and invertebrates - meaning those tiny centimeter long pests can quickly eat up colonies of shrimp, as well as fry or smaller fish. Hydra use their tentacles to sting and immobilize adult shrimp. The tentacles of Hydra are covered in small, stinging cells called nematocysts, which can release toxins when triggered. When a shrimp or small fish comes into contact with the tentacles, it can become paralyzed or even killed by the toxins. While not always deadly, Hydra can cause damage to the delicate tissues of shrimp/fish through physical contact, causing irritation and even abrasions on the skin of shrimp, which can lead to infections and other health problems.

How to Get Rid of Hydra

Getting rid of Hydra can be challenging, but it is possible with the right approach. One of the easiest ways to get rid of Hydra is to remove them manually. This can be done by using a fine net, tweezers, or a siphon to scoop them out of your tank.

Another method is to reduce the amount of food available to Hydra by feeding your aquarium inhabitants less. You can also introduce predators, such as certain species of fish, that will eat Hydra. Some of these include Siamese Algae Eater - These fish are excellent at controlling Hydra populations and are known to be effective hunters. They are also peaceful and easy to care for, making them a popular choice for many aquarium owners. Dwarf Chain Loaches, Bristlenose Plecos, Cherry Barbs, and Guppies. It is important to note that while these fish are known to feed on Hydra, they may not completely eliminate the population.

Chemical treatments are also available, but they should be used with caution. Some chemicals can be harmful to your aquarium inhabitants, so it is important to follow the instructions carefully and monitor your aquarium closely. If you decide to use a chemical treatment, be sure to remove any sensitive organisms from your aquarium first.

Overall, while Hydra is certainly an interesting organism, it can also be a threat to your aquarium and its inhabitants. If you notice Hydra in your aquarium, it is important to take action to control their population. By using the right methods and being vigilant, you can keep your aquarium healthy and free from Hydra infestations.

Image Credit to Shrimp Science

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