i had to train the flagtail
he has only ever sucked on one ray when she was preg as soon as she had pups he stopped it was like the movement of the unborn pups attracted the flagtail
when he started to suck i used to tap on the tank glass then i chased him around with a stick if he sucked
after about 2 weeks the flagtail knew if he sucked something bad would happen to him
that was years ago i have had the flagtail for 6 year+