I need to know why a 6 year old red parrot fish would suddenly turn black around his mouth & dorsal fin?

Question

There are three red parrots in the tank, well established as I got these guys as babies and they have passed the 6 year mark. Presently only one of them has the black markings on him.
I am thinking maybe stress?
I have many tanks and can consider separating them, but that may be stressful to them also as they have never been apart. Any suggestions from experienced aquarists?
Thanks

Answer 1

I'll agree with Catxcatxx on the ammonia part. Black is a sign of healing, though, so it sounds as though there might have been an ammonia spike (major water change or cleaning lately?). This could also be caused by some fighting between the fish that is now healing.

Look at the info for "black patches" in the link below (tuberculosis is also listed as "Piscine tuberculosis"):

http://www.fish-disease.net/diseases.htm

Answer 2

black often indicates burn type marks, what are the ammonia readings in your tank? that's what i'd check first, anything more than 0 would be the culprit. what size tank are they in? blood parrots need quite large tanks as they grow deceptively large (about 8" or so).

does it look like its under the scales, the scales themselves or something else? no other symptoms such as lethargy, losing weight, bloatedness?

the reason i ask is sometimes black marks, specifically in cichlids (a blood parrot is a cichlid) can indicate fish tuberculosis, which is a nasty disease, sometimes even symptomless, and is usually fatal. have a look at the link below.