like is said already, you NEED to take them back, or get one hell of a large tank/pond within a couple months.
take it from me, and i know a good amount about pacu, a 55g is is no way shape or form even 1/10 of what pacu need. once they hit 6-8 inches (which will be within a couple months) they hit a growth spurt where they go from that small 6-8" to 16-18+ within a whole 2 months, maybe 3 at most.
to put it easily, a pacu will be 1/2 as long as that tank, and close to twice the width within a year. so no, a 55g is not suitable.
take it from me, and i know a good amount about pacu, a 55g is is no way shape or form even 1/10 of what pacu need. once they hit 6-8 inches (which will be within a couple months) they hit a growth spurt where they go from that small 6-8" to 16-18+ within a whole 2 months, maybe 3 at most.
to put it easily, a pacu will be 1/2 as long as that tank, and close to twice the width within a year. so no, a 55g is not suitable.