Understood Bill, my observations are that RES are very likely better adapted to low light level conditions than LMB. From what I have researched LMB eyesight is roughly five times more sensitive to light than human beings. Not having eyelids or the ability to adjust their pupils very much means RES likely do not see well enough to chase fast moving prey items during normal daylight. RES do behave very differently when the lights go out v. when the lights are on. When the lights are on they consistently stay as far away from my aquarium light as possible and they mostly stay in the bottom half of the tank. They also very seldom chase FHM when the tank light is on. Once the light goes out they spread out and move up to the top half of the tank and start chasing minnows. The vast majority of FHM eaten by my RES are in very dark conditions in my basement.
So far I have not dropped any snails in the aquarium to see how they react but I can tell you that snails were noticeably absent from my pond last year. Adding snails to the aquarium is not likely to help with foraging when I turn them loose. I can also tell you that despite my best efforts fishing nightcrawlers deep and slow last year I was only able to catch a single 4" RES from my pond in 2013. The bulk of my forage base last year was YOY GSH and I am confident that my larger RES are utilizing them with the absence of snails in my pond.
I have read the study on RES utilizing different sizes of snails and size preference, I found it fascinating. I have observed a similar size preference with them eating FHM. Gape wise an 8" RES can easily inhale a 3" FHM but the tail always protrudes out of their mouth and they usually spit it out. When eating smaller and shorter FHM that they can completely fit in their mouth they will pop their jaw hard three times as they "crush" the FHM down their throat, I see lots' of small FHM scales come out of their gill plates as they are popping their jaw and crushing a FHM. IMO it is not just the gape size that limits RES predation on small fish, but overall length also plays an very important role, a small fish needs to fit completely in their mouth.
Back in college I did senior level term paper on �Perception and Predation in LMB� for one of my Psychology classes. In that paper I hypothesized that the near sighted visual system in LMB is what triggers a
fixed action pattern (FAP) of opening the mouth and inhaling a prey item. My thoughts are that this is the reason my RES do not chase FHM when my aquarium lights are on, bright lights impair their abilty to judge depth and distance. LMB do have a very short and small area several inches in front of their mouth where they are quite capable of binocular vision and depth perception when both eyes are turned forward. IMO it is this small area of binocular depth perception that serves as the trigger of a FAP in capturing prey.
