Hi everyone. Please help. Someone eating the tail

[Ligita]

Please help! I was given a fish and don't know what it is and how to look after it. Since I got it, fish changed colour and her tail looks like someone has eaten it. What to do?

 

[fluttermoth]

We really need to know what kind of fish it is to properly help you; can you try and get a picture of it?

Is the fish in a tank with a filter and a heater?

The first thing to do is change some of the water; good, clean water is the best 'first aid' for fish, but you do need to make sure any new water is warmed and dechlorinated, so I hope you've got something to make the water safe.

 

[Ligita]

There are filter, heather and oxygen ( I'm not sure if I called it correctly). I have this aquarium for almost 10 year and never had this situation before. I could not take clear picture of my fish, so I found it on internet. This fish behave very strange, swims like crazy

 

[Jake3030]

That would be a cory catfish or corydora. I agree the best thing you can do is a water change. What are the water parameters and is there other fish in the tank. It would also help to see the tail that has been "eaten".