I Want BumbleBee Babies!

-bump-

Here's some links that may help (if you haven't gotten an answer already...)

http://www.aquarticles.com/articles/breeding/Bridges_Bumblebee_Goby.html
http://www.aquaticcommunity.com/gobyfish/bumblebee.php

I believe you would need to acclimate your gobies to brackish conditions in order for them to spawn. There are several goby species commonly referred to as bumblebee. A couple of them are true freshwater species while several of the others are brackish that can only tolerate freshwater. You most likely have one that prefers brackish conditions, as the true freshwater species don't seem to be commonly sold for most people.