Bumblebee Gobies come in 2 different species (that I know of).
There is the Brachygobius Xanthona and the Brachygobius Nunus.
Brachygobius Xanthona has perfect unbroken black stripes. They are best suited for Brackish, but will "tolerate" freshwater.
Brachygobius Nunus has less perfect stripes (sometimes even broken stripes or black spots). This one MUST have Brackish water.
When it is said that a Brackish fish can tolerate freshwater conditions, it should be noted that "tolerate" generally means "live with random illness".
You should be keeping either of the Bumblebee species in Brackish water.
That said, I have mine in 1.010sg, which is usually considered a little high. - other fish live in the tank.
BBGobies are very territorial, and will not school with other fish. When kept in numbers, they tend to wage small battles with each other, establishing the borders of their territory. As long as they are not overstocked, this generally doesn't lead to any damage, and can be quite entertaining to watch.
BBGs tend to fin-nip, as they are ambush predators and will jump at just about anything that happens by.
There has been much success keeping them with various brackish puffers (on the smaller side). While it is usually not recommended to keep anything with puffers, they tend to leave the BBGs alone. I've found that this makes feeding easier -- BBGs can be difficult to feed because of their size and "ambush" tendencies. Puffers are notoriously messy eaters, and the falling food debris attracts the attention of the BBGs. Mine just sits below the puffer during feeding time.
If puffers aren't your thing (they have their own care issues), several BBGs in the same tank will afford you endless entertainment.
I've also had success keeping them with Black Mollies or Sailfin Mollies in Brackish conditions. You will, however, notice some minor fin-nipping with the Sailfins, and fry won't last long.
Hope this helps!
