Probably not the best idea. Watchmen gobies, especially the yellow's can be very territorial and aggressive. I had a mated pair of YWG until one day the male decided he wasn't in love anymore and killed the female. He's a terribly aggressive fish to my Sleeper Banded Bullet Goby(aka Dragon Goby) and he also recently killed my spotted mandarin. This all occurred in a 155G, I wouldn't risk it.