Small  or huge (some are 300kg!)….. I saw once a cod potatoe so huge that at first I thought it was a shark! The groupers are usually solitary, they hide day time in hole of the reef and in the evening they are “top” predators of fishes. Most are hermaphrodite they born female and became male later on. They are so many kinds (59 kinds in red sea)  …. here some exemples of type and colors….
Cernia maculata, Mérou loutre, Arabian grouper

Cernia a punte nere, Mérou pointe noire, Blacktip gouper

Cernia corallina, Mérou rouge, Coral grouper

Cernia celeste, Vielle cuisinière mérou, Peacock hind