We have had a couple of bumblebees for a while now. We experimented with different foods, but found that while they would hit the flakes and pellets, they would spit it out.
What ended up working very nicely for all the fish in the tank is frozen brine shrimp. My fish are all small, including the gobies, so I slice the cube up with a razor blade. THis makes nice goby/guyppy/danio sized tidbits. I defrost it in some warm water in a cup and pour it into the tank in waves. This gets the attention of the gobies who seem to be a little slower then the other fish figuring out whats going on. As long as I just pour a little of the shrimp "soup" in the tank at a time, hardly any of the chunks reach the bottom. It also lets us more easily gauge when the fish are "done" although our catfish seem ready willing and able to deal with left overs.
We only do a shrimp feeding every couple of days. Before we found the shrimp the gobies were doing ok, we suspect eating the fry of the constantly spawning danios. However, since feeding the tank sliced brine shrimp they seem to be doing better.
Thats my experience, anyway. From what I have ready different gobies have different degrees of tolerance for flake food.
Regards,
Artuk
PS- Our tank is freshwater, and they have been doing fine.