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Do hydra have any impact on nano fish's health?


Schuyler
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Most places that talk about hydra will say that they only ever kill tiny fry or shrimplets (and even that seems to be slightly debated).

But I imagine getting stung by them often could have add a level of stress.

Do they have any impact on the fish or is that just me projecting?

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I have never noticed an impact. I don’t mind them and they are a natural part of an ecosystem. I keep things as small as Least killifish and Celestial pearl danios. I hatch CPD eggs in fry tanks with hydra. They all grow strong and healthy. The fry never hide and are very bold. If they were incredibly stressed they would hide. 
That being said I would not want a tank where every square centimeter is covered. 
All of my tanks including the fry tanks also have neocaridina. If hydra cause shrimplette loss it is not noticeable to me. I give dozens of shrimp away and feed them to other fish because they overpopulate regularly. 
Hope that helps answer your question. 

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On 12/9/2022 at 10:43 AM, Schuyler said:

Most places that talk about hydra will say that they only ever kill tiny fry or shrimplets (and even that seems to be slightly debated).

But I imagine getting stung by them often could have add a level of stress.

Do they have any impact on the fish or is that just me projecting?

If it were to happen, I imagine it would be an extremely rare situation where maybe a small fry was already injured or ill, and not mobile. Generally, it is not an issue, and some fish even eat them. 

Here is an article on our website about them: https://www.aquariumcoop.com/blogs/aquarium/hydra

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I have seen large patches of cell death occur on the body and kill many fish up the 3 or 4 inches long in circular tanks where the fish continually pass by a patch of thick, pink colored hydra and get stung over and over, probably hundreds of times a day. So it's possible but something that extreme would not likely happen in a typical aquarium. I have seen a small green colored hydra kill a newly hatched fry in an aquarium. But I've only seen that happen once. Fry usually seem smart enough to stay away from hydra.

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