What is wrong with my fish? Has anyone experienced this before?

[HarryDk]

I have him 8 months ago at 3", he is now 6.6", eating well, active, bossy and getting redder.
However, for the last few weeks, his left side develop some weird discolour curvy pattern under his fin as marked in the photos. I do big water change twice weekly 80%+ each and nitrate stay below 10. Please tell me this isn't something serious :huh:
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[jmf3460]

Harry this appears to be just the coloration of the fish and nothing disease related.

[HarryDk]

THanks, just the pattern become clearer time to time that concern me, well, will just keep my eyes on him

[donnacona]

At 8 months I think that maybe it could color changes due to preparations for breeding

[HarryDk]

At 8 months I think that maybe it could color changes due to preparations for breeding

he has been fertilizing eggs for a while now, but only start change color recently .. hmmm