Gars

One gar stocked: the S.A. Mosaic Gar, listed in all three tiers. It is a surface-hugging pursuit predator with a long jaw full of small teeth, which means it hunts by chasing rather than ambushing and needs length of tank more than it needs depth. Buy it for a wide, well-lidded aquarium with open swimming room and calm tankmates too big to fit crossways in that beak.

Two things sink these fish. They spook, and they hit the glass or the lid at speed, so a damaged snout is the injury to watch for; dim the room before the lights come on. They are also stubborn about frozen food at first. If you would rather it be eating before it comes home, start with the quarantined listing.