[Delphinus]

What does your overflow look like. Can you add an extra layer of eggcrate maybe?

I found when setting up my 72g, I was absolutely paranoid of fish getting into my overflow. I siliconed in a piece of plastic over the extra cut-out (I can have my sump return in one of two positions), and I cut a piece of eggrate to fit the curve of the curved wall (it's a curved overflow). But eggcrate alone will not stop slender bodied fish such as gobies, jawfish, firefish (who are all notorious jumpers, too), so .. I sewed some fiberglass window screening onto the eggcrate.

Doesn't really matter what drives them to do it ... what matters is what happens when they try. Maybe he's being chased, maybe he's looking for food, maybe it's just fun like a waterslide. Who knows.

I remember I once had a fish that Big Al's called "The World's Greatest Algae Eater" (which, incidentally, I thought was The World's Dumbest Sounding Fish Name Ever, and also indicentally, ironically, whatever, was WRONG ... unless .. maybe I just somehow ended up with The World's Worst, The World's Greatest Algae Eater ... anyways I digress. Although he never touched algae, he had a really hilarious personality). Imagine a fish that looks a little like a shark (only about 2" long). He can blink his eyes which I thought was neat. Anyways when he thought I wasn't looking, he'd sometimes swim back and forth through the bubble wall in the back of the tank. I could swear he was doing it for fun. I couln't really see any other reason why he might have done that. Probably like running though a sprinkler or something. Anyways I guess all my point is, I don't know for sure, but it wouldn't surprise me that fish sometimes do some certain things, because it beats doing other certain things (i.e., maybe it's more enjoyable than bumping into the glass or something). Anyways it's just my thoughts ... I'm for sure no fish psychologist so I could just be way off base...