Damsel damaged fins Turing black

[Fishology]

Not my tank or fish but I have a friend with a damsel she just bought a couple days ago, she said when she added him tor he tank he was fine but a little later the find where damaged and started trying black, I have never heard of this in fish or seen it. I think it my be rotting the the fin is dying off. But I don’t know much about fish illnesses any help?

 

[Jay Hemdal Verified Community Expert]

Not my tank or fish but I have a friend with a damsel she just bought a couple days ago, she said when she added him tor he tank he was fine but a little later the find where damaged and started trying black, I have never heard of this in fish or seen it. I think it my be rotting the the fin is dying off. But I don’t know much about fish illnesses any help?

Hi, I just saw your message (I manage the fish disease forum, but this was in a different area)

Most fin damage is caused by tankmate aggression. In order for us to try and figure it out, we would need pictures, as well as more background about the tank, what fish are in the tank, etc. This post explains all that:

https://www.reef2reef.com/threads/s...sease-treatment-and-diagnosis-section.775547/
Jay