I love jacks... I wish my 9 inch monster at home did not have a torn dorsal...I was at the lfs today, picking up bio-spira to get my 30 cube ready for the flowerhorn... and i couldnt help looking at the JDs... I found one that was just inrecredible, i couldnt leave without getting him.. he is one inch and was terrorizing every other fish in the tank. He already has prodiment red on his fins and i might have to keep this guy for the long hall being that he is such a good specimen. When picking out dempseys i believe its best to go with ones who are not displaying dark body tones but whole have dark spotting. The dark spotting indicates good health, and the light body shows that he is not stressed at all.. this guy though he was just a little bad ass, and is fearless of anything... all the others were dark. He has been attacking his reflection ( i got a cool ass picture) and my finger all afternoon!
Based on my observations of my own little Dempsey, who I got at 1.5" and has since gone to 3.5" over the 3 months ive had him, dark coloration is the coloration used when in Aggressive mode, and light coloration indicates fright and stress.
He is the undisputed dominant fish in my 55g cichlid tank, and when cruising about he is constantly dark. When I do water changes and remove all the decorations from the aquarium, robbing him of his desired hiding places (he never purposely shows himself when he knows I or any other person is near the tank, always hides and won't come out for 10 minutes or so till he thinks everyone has left) he is a very light color.
Well they do tend to blend with their surroundings too... I used to have a dark green plant and my bigger guy would match it when he was little... but now he is a pinkish color with baby blue scales... Im trying to get my hands on a EBJD breeder. The ones that a half Electric Blues and Half JDs are the most valuable dempseys... really cool looking too