well assuming the synos are larger than the BGK, they will be fine...i would find it hard to believe that a BGK (even full grown) could fit a large syno in its mouth...if they are still small, i would be weary, but they do grow pretty fast (syno eupertus grew from 1" to 4" in 7 months) ....but i hope someone will chime in if they know of the contrary!