Black dots

[Rick147]

I noticed most of my rainbows have a black spot.
I’m not sure if this is part of their colours or not?

 

[itiwhetu]

Just part of who they are.

 

[Colin_T]

Just normal colouration for juvenile fish

The only 2 health issues that produce black dots in fish.
One is black patches that are caused by chemical burns (chlorine/ chloramine, overdosed medication or fertiliser.

And two is a parasitic worm that is occasionally found in some wild caught fish and they might have 1-10 small black dots about 1mm in diameter. These parasites can occur anywhere on the body but are usually found in the rear half and rarely on the head. There's no treatment for this and the worms spend their entire life in one section of the fish and don't change.