I have had my 37 gallon tank setup for around 8 months now without any problems. I have 6 Danio Zebras, 3 Cory Catfish, and 6 Neon Headlight fish. 5 of my Zebras have grown to about 2 inches long, but the 6th has not grown at all and is now not looking healthy. He or She has a shrunken stomach and hangs out in the dark corner all by its self. Should I keep it in the tank or get rid of it? I don't want to kill it, but I'm not sure how to help it. Is it just old age? I think the life span is around 2 years for these fish. Maybe some counciling with a dietition?