I have about 10 fish (protomelas virgatus if you like being technical) in a tank. how exciting. anyway, whenever i go to bed, and i turn all the lights off, i hear massive splashes at the top, as they go crazy as soon as the lights gone, trying to jump out. 2 have died like this, and another has jumped out that i frantically picked up and put back in. but now i have all escape routes blocked off decently well. they have always done this. why ?