Boxfish, Trunkfish, and Cowfish (Family Ostraciidae)
With their rigid bodies propelled “helicopter fashion” by tiny, rapidly moving fins, these fish are an amusing sight as they motor about the aquarium. Their appeal is heightened by an “alert” face, and, in many species, horn-like projections at the head and rear of the body (see color insert for photo).
Although immune from attack by most large predators due to their hard covering of bony plates, box-and cowfish are slow moving and their rapidly undulating fins seem to draw attacks from smaller fish. The skin over the rigid plates is, strangely, quite sensitive and also suffers from the attentions of aggressive tank mates.
A brilliant yellow body highlighted with blue spots and set off by “horns” at the head and rear renders this droll fish instantly recognizable. Slow feeding and peaceful, they do best with similar species and are one of the few fish that will coexist with seahorses. They are quite entertaining as they cruise about, hovering as they examine their homes for their favorite foods, algae and crustaceans.
Many species of cow-, box-, and trunkfish are, despite their apparent calmness, quite excitable. Frightened fish will release a chemical into the water that is toxic to most other fish. Establish them in the aquarium before you add other fish, and in a dark room, turn room lights on before switching on the aquarium lights.
This species' mode of swimming truly fits its name, with only the fins fluttering, propeller-like, to move the rigid body along. They are extremely inquisitive, seeming to notice and examine all happenings in, and even outside of, their aquarium. Growing to only 4 inches in length, hovercrafts do best when kept with nonaggressive fish. Because they are often slow to feed, their condition should be monitored closely — thin animals rapidly develop a sunken stomach area.