'pineapple trigger' is a catch-all name. There are three triggerfish sold as such: Pseudobalistes flavimarginatus, Balistoides viridescens and (rarely though) Abalistes stellatus.
In any case you most likely have a fish that will grow to over a foot in length (with teeth to match) given enough time. If it is the P.flavimarginatus (pic 1 - sub-adult) , it will be unsociable but never aggressive. If it is B. viridescens (pic 2 sub-adult), it will be more like a 'fear-biter' if you are familiar with dogs at all
- only biting if cornered, otherwise passive - until adulthood at which time it will turn ravenous. A. stellatus (pic 3 - juvenile) is new to the hobby, so I cannot comment on behavior.
I suspect your tang knows this fish is a threat - and is trying to get him out of his territory! How big is your aquarium??
Hi, I got a Pineapple Trigger juve about 4 days ago and when I introduced him into the tank my yellow Tang started picking on him and has not let up since. The trigger is bigger than the Tang, but all he does is hide. When the Trigger did come out to eat the Tang attacked him yet again. I tried takeing out the Tang and leaving him out for about 20 mins and then put him back. As soon as the Tang seen the Trigger he attacked him again. Now, my Trigger will not eat or swim. All he does is hide with his face burried in the rock. He was trying to eat yesterday, but now he won't eat at all. Please help me figure out what to do because I really do not want to see this beautiful Pineapple Trigger die. 
