My male Bristlenose Pleco doesn't seem happy? His side hooks are always out?

Plecos get territorial around other plecos, they hate each other, and have been known to kill each other. 16 gallons is too small for one pleco, 2 plecos in a tank that size would be very stressed. I don't know If the pleco would do better in the 55 gallon tank, it is very poorly stocked. This might be a situation were re-homing the fish to a friend, to someone on craigslist, or to a Pet store would be the most humane thing to do.