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bluegill coloring

About 2 weeks ago, I got a dozen 4-6 inch bluegill from a friends 1000 gallon tank and moved them into my 60 gallon tank. They all had a dark color to them originally, but after being introduced to my tank now, I would say about 50% of them are now very lightly colored. Any ideas what this means? I couldn't seem to find much on this in the bluegill/centrarchidae literature.

Other than size of tank, much of the parameters were matched. Both tanks at 70-73 degF, same pH. I did have about a 6 day spike in nitrite up to 1ppm, but I gather centrarchidae are fairly tolerant of that. They didn't eat for about 12 days after the move, but are eating fine now and active, and look healthy.

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Permalink Reply by chuck on January 29, 2012 at 10:42am

my firt guess will be the amount of light that gets in the tank is less than your friends, they will loose some color if kept in dark. stress will do that too for a while. i moved a few small tilapia that were pale to a friends fish tank and there color came right back, but he ffeds them nice flakes from the pet store, ????

Permalink Reply by Chi Ma on January 29, 2012 at 10:44am

If you give them some cover they will color up. They get pale when there is no cover or if they are are over crowded.

Permalink Reply by Claudio J Tracchia on January 29, 2012 at 3:13pm

It may be like tilapias they change accordingly to the color of the tank my tank has white lining and the fish change from dark to light grey. Am also getting blue gill in a few weeks keep in touch, CJ

Permalink Reply by TCLynx on January 31, 2012 at 1:25pm

Well when I had Blue Tilapia the coloration of the fish seemed to be linked to stress, the tank color, and/or mating. They would get dark when stressed or when the female was getting ready to release fry. They would lighten up and get red tones when feeling frisky. Etc.

My bluegill have been mostly in dark tanks and they seem to stay dark but the ones moved into the IBC tank seem kinda pale so maybe it is also trying to match their background.

Permalink Reply by Glenn Davis on October 25, 2012 at 8:53pm

I was told today by a biologist at my local fish hatchery, that when the bluegill are a lighter color they are healthy and not stressed, when they darken up they are less healthy and are a bit stressed. I don't know personally about this, and this might be for the specific hybrid bluegill he raises.

Permalink Reply by TCLynx on October 26, 2012 at 7:58am

Yes and no. It is really quite common for dark coloration of many types of fish to indicate stress. I know it can hold true of tilapia as well. But that is not the only thing that might cause fish to exhibit dark coloration. Environment will likely tend to affect coloration as well. Fish will try to blend in as well so I wouldn't assume that a dark bluegill in a black tank is necessarily stressed out. I expect the coloration could also vary with season and mating behavior. I know it does in tilapia.