Illness or injury? Danio

I noticed this morning some red spots on my danio.
Unsure if it's illness or injury.
What should I do?

Parameters
pH 7.5
Ammonia 0
Nitrate 0
Nitrite 20 all ppm
Temp 25°c

It appears to have dropsy… in my experience api melafix works
Perhaps there is too much nitrates?
Or other fish are biting it as mating

Just a heads up, you've switched your Nitrate with Nitrite.

Your Nitrite should always be 0 --> if it were actually 20ppm everything would be long dead.

With that being said, 20ppm Nitrate is too high. The lower to 0 you can get it, the better. I would recommend doing a water change to reduce that amount.

As far as the Danio goes, I've never seen marks quite like that. It almost reminds me of an ammonia burn, but since you stated our ammonia is 0 that's not possible. I do not believe it's an injury from another fish - the bite marks are too small. Out of curiosity - what are it's tankmates?

I have had good experiences using Melafix to treat odd issues like this and it's typically pretty effective. I would definitely wait to see if someone can positively identify what is going on and if they cannot, Melafix may be a good choice along with frequent water changes.