Mood is probably the wrong word as it implies a human type emotion.
But some types of fish really put on a show. When approaching other fish of their species, when they are in the mating mood. When they are approaching divers or divers are approaching them. When danger is nearby.
Filefish come to mind. Scrawled filefish have irredecent blue stripes they can turn on and off, go from light almost washed out to dark. White spotted filefish are blocks of orange, white and brown but can instantly go to a white spotted background and often flash their spots at divers. A very curious fish that if feeding can be aporoached closely while they change colors and keep a wary eye on you. Both of these species in the two or three pound range. Then the tiny slender filefish that can get up to 4" but more commin size is 1 to 3". Masters of camouflage, most divers never see them unless pointed out. They are solid color and only go from light tan to dark brown, but as they float in amongst a grogonian they blend in so well you can be looking directly at them one moment and loose them the next. If they drift from one color (what looks like a plant but is actually an animal) to the next they can change shades like flicking on a light through a dimmer switch. The transition blends in perfectly from one background to another.
The one really cool thing about staying in the same place for an extended time (vs diving a reef once and leaving) is you really start getting into the fish behavior. The reef in front of our room is as familiar to me as my own ponds. I dive it at least once nearly every day. So I see many of the resident fish over and over. Some species, like some of the puffer family, will get almost sociable with divers. I played hide and seek with one one time while other individuals are standoffish. One resident turtle is so used to divers my wife was able to take macro pictures of its head while feeding with the camera 6" away. It would look up at us once in a while then go back to ripping at something under a coral head with its beak it was intent on eating. I see that turtle probably once a week as it passes through the general area. The reef out front is like my own back yard with the pond.
Treated to a pod of dolphins passing through at breakfast this morning.
Life is good.
