Danio tail bitten off

[Psychotic Cloud]

Hi! I recently got a few danios and added them to an established tank that had a betta in it and I’ve never had a problem with the betta mixing with other fish. Now they have been in the tank for about 2 days and one of the danios had the top half of his tail bitten off and I found him stuck upside down on the gravel at the bottom of the tank unable to swim properly (he will try and as soon as he’s upright he flips over again). Currently I have moved my betta out of the tank but I don’t know what to do for my danio because he’s struggling and can’t really swim at all and will just lie at the bottom of the tank. What do I do? How can I help him?
Side note- only one of the danios was attacked not any of the others and he’s the only one that was a different colour.

 

[Colin_T]

Hi and welcome to the forum

Siamese fighting fish are solitary fish that don't normally do well with other fish. They can get quite aggressive towards intruders in their territory, which usually encompasses the entire tank, but especially the upper half of the tank where danios swim. They also don't like fast moving fishes like danios, or brightly coloured fishes like male guppies.

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If you can post some pictures and a 1 minute video of the sick/ injured danio, it might provide us with some more information. You can upload videos to YouTube, then copy & paste the link here.

If you use a mobile phone to film the fish, hold the phone horizontally so the footage fills the entire screen. It makes it easier to view the fish

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How long has the tank been set up for?
How long have you had the danios for?
How many danios do you have?
What other fish are in the tank?
Have you added anything to the tank in the last 2 weeks, besides the danios?

What is the ammonia, nitrite, nitrate and pH of the aquarium water?
What sort of filter is on the tank?
How often and how do you clean the filter?

How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the tank?