Really fat danio.

my zebra danio has developed a rather large belly, i am quite alarmed because it seems to be getting bigger. Is it because it always steals the others food?

Maybe its pregnant?

wow, i hope so, but alas, i have no fry food or another tank to keep them in. They will get eaten alive!

Get a tank (maybe like 5 Gallons) at petco or petsmart, buy a small heater and filter, and search for some websites to help you.

Female danios can develop eggs quite readily in an aquarium. Unfortunately if they don't breed and get rid of the eggs, they become egg bound and remain fat for the rest of their lives. They also become unable to breed. This is one of the reason they should be kept in groups.

When danios breed the males chase the females and nudge or headbut the females belly region. This is to induce the female to lay. Then the pair will swim thru some plants and scatter eggs & sperm.
The eggs sink to the bottom and hatch after a few days. The fry hang on the glass for a couple more days before becoming free swimming.

I've seen chickens and ducks become eggbound, but fish?

http://www.tetra-fish.com/forums/showthread.php?p=36085

http://www.fishchannel.com/fish-health/freshwater-conditions/weddings-and-funerals.aspx?cm_sp=InternalClicks-_-RelatedArticles-_-fish-health/freshwater-conditions/weddings-and-funerals

I don't know.

Yep danios are renowned for it. They normally occur in cool water, (not cold just cool, mid to high teens Celcius) and as soon as it warms up the females develop eggs and they start breeding. Unfortunately when they are kept in tropical tanks all the time, the females develop eggs and the lack of temperature variation stops the males from coming into breeding condition. The females have eggs but the males aren't interested. So the females become eggs bound because no-one will spawn with them.
High calcium levels in the water can also cause it but is much less of an issue than constant warm water.

Birds usually become egg bound due to lack of calcium and exercise. It happens a lot in caged birds that don't have a properly balanced diet and get limited exercise. When the same birds are kept in an aviary and given plenty of cuttlefish bone or shell to peck at, the problem normally goes away.

I'm pretty sure the danios can't really die from it, right?

danios don't normally die from being egg bound. They just get fat and stay fat. They swim around and feed like normal and they can live for a few years. But mainly they just end up looking like fat danios.

LOL then nothing's wrong, right?

as long as the fish is still swimming around and eating well you have nothing to worry about except a fat little danio She will be fine, she just won't become a supermodel.