Yes it is possible. Glo fish Is just a zebra danio with some jellyfish DNA. They don't really get pregnant however. The females can get plump with eggs. Danios can also have dropsy which is retaining water for any number of bad reasons. Dropsy is a symptom not a disease and is often fatal. Basically if the fish is eating and swimming like normal and engaging in the typical chasing and playing that danios often do, then it may be a gravid female. If it seems unhealthy and hides or doesn't move around much and hasn't been eating then it is probably dropsy and could be treated in a hospital tank (often not successful) with a broad spectrum antibiotic like maracyn plus. It seems that recently sold glo fish are given hyperbaric treatment to render them sterile. This makes it more likely that you might be seeing dropsy.