why doesent my gerbil ride his wheel?

from what i saw of your you-tube video 'is my gerbil pregnant' i would say that that wheel is much to small for them. they probably don't use it because they don't fit.

also the wire rung wheels like the one you have, are considered dangerous to small pets due to the number of cases of animals getting their legs and tails trapping and suffering injury.

maybe try a bigger wheel with a solid running surface?

hope this helps

Myn is all plastic with no gaps and myn runs in it like mad! I wounder if your advice worked??