Many have mentioned the lionfish seems too small... keep in mind that real life aquarium fish can be purchased in all sizes. All fish, even the huge ones, start out small. Juveniles are often more colorful than the adults, and are more likely to acclimate to captivity. Also, when you buy your fish young, you get to keep them longer (many have short life spans).
Jim has apparently decided to create all juvenile fish for this screen saver. This creates a nice balanced tank. In real life an adult lionfish would have snapped up all the others in his huge mouth.
Jim, for your next project you might consider creating a new aquarium that focuses on large agressive fish, such as an adult lionfish, moray eel, cat shark, stingray, etc. Of course you'd have to scale everything down to fit, but the idea would be to model a 200-500 gallon tank. Just a thought...though you probably don't want to talk to much about the next project when you're recovering from all the long hours put in on this one
Also a comment on the lionfish side fin movement...I've noticed the most realistic movement is on my laptop at 25 fps. On my desktop at 70 fps the fin movement is more rigid. Jim has already posted why this happens. I believe Jim plans to tune this further...perhaps link it to the system clock instead of frame rate...though I'm not a programmer...
This version is looking very nice on all my machines...makes me want to go diving