Found this bug with the Emperor Red Snapper. When you capture a tropical fish and place it down, it sometimes doesn't show the pattern and looks like just a white fish. Not sure if this matters or is intentional.
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Misode
tryashtar
MC-197328 maybe?
Avoma
I agree with tryashtar. This appears to be a duplicate of MC-197328.
migrated
Are you using a resource pack? I can't seem to be able to reproduce this