Caution should be used when deciding if you want to keep a poisonous fish. Some species not only have the ability to inflict a venomous sting that kills other animals, but many can cause toxic poisoning in an aquarium which can result in the death of the other tank inhabitants, not to mention themselves.
While Boxfish and Cowfish cannot sting you, they can exude a toxin from their skin which can poison an entire saltwater aquarium in just a few seconds.
Female Spotted Boxfish (Ostracion Meleagris)
ifish/Getty ImagesThe White Spotted Boxfish (ostraction meleagris) (also known as the speckled boxfish or freckled boxfish) has a hard, rectangular shaped body, thus giving it its name "Box" Fish. It uses a small dorsal and anal fin to propel itself through the water, at which time it curls up its tail on one side or other of the body. The mouth region protrudes from the front of the body, looking similar to a snout with a small mouth at the end.
The female has a brown body with white spots and is pretty plain compared to the males whose body is basically brown with bright blue sides marked with golden spots and white spots on the top. The females will turn into males like a lot of fish species do to propagate their species. They are common on shallow reefs and reach 6 inches in length.
Male Spotted Boxfish (Ostracion Meleagris)
ifish/Getty ImagesHere is a male Spotted Boxfish (Ostracion meleagris) which is common on shallow reefs and reaches 6 inches in length. Males are dark blue with orange markings and black above with large white spots. The Hawaiian form has fewer orange spots than those elsewhere.
The Box Fish is shy and quiet fish. It likes to live around rocks and corals as a bottom dweller, a lot of times around sandy bottoms. It is generally slow moving, but have you ever tried to catch one in your aquarium without sending it into a toxic emitting frenzy?
Female Whitley's Boxfish (Ostracion Whitleyi)
Keoki StenderA Female Whitley's Boxfish (Ostracion whitleyi). Brown and white females are fairly common. Sky-blue striped males are extremely rare and generally found in deep water. It attains a length of 6 inches but is usually smaller. This species may not sustain a breeding population locally.
Male Whitley's Boxfish (Ostracion Whitleyi)
Timothy Ewing/Getty ImagesA Male Whitley's Boxfish (Ostracion whitleyi). Brown and white females are fairly common. Sky-blue striped males are extremely rare and generally found in deep water. It attains a length of 6 inches but is usually smaller. This species may not sustain a breeding population locally.
Longhorn Cowfish (Lactoria Cornuta)
Raimundo Fernandez Diez/Getty ImagesThe Longhorn Cowfish (Lactoria cornuta) inhabits the reefs of the Indo-Pacific, usually in the calmer waters as it is not a strong swimmer. The body is tan to yellow and covered with white and blue dots, and is occasionally referred to as the Yellow Boxfish; however, the Longhorn is not to be confused with Ostracion cubicus, commonly called the Yellow or Polka Dot Boxfish. In the wild, it is not uncommon to see a 20" specimen, while in the aquarium the Longhorn Cowfish tends to be dramatically smaller-16" or less.
Longhorn Cowfish (Lactoria Cornuta)
Daniel Rocal - Photography/Getty ImagesSimilar to other boxfish. the Longhorn Cowfish's skin is poisonous and, when threatened, it will release a toxin which is lethal to other tank members, including itself and other Longhorns.
Spiny Cowfish (Lactoria Diaphana)
Izuzuki/Wikimedia Commons/CC BY-SA 3.0The Spiny Cowfish (Lactoria diaphana) is rarely seen on deep rubble reefs in Hawaii but is fairly common in the waters of Japan. It has a convex belly and short spines and attains a length of 10 inches. It has been recorded from scattered locations throughout the Indo-Pacific.
Thornback Cowfish (Lactoria Fornasini)
Tony Shih/Flickr/CC BY-ND 2.0The Thornback Cowfish (Lactoria fornasini) is uncommon and well-hidden among sandy rubble and seaweed. It is usually less than 3.5 inches long. This fish has two prominent spines above the eyes and bright blue lines may be present. The Thornback Cowfish is common in Japan.
Smooth Trunkfish (Lactophrys Triqueter)
Humberto Ramirez/Getty ImagesThe Smooth Trunkfish (Lactophrys triqueter) is fairly common on sandy reefs. Juveniles are black with large white dots. This fish attains a length of about 12 inches. It is found in the western Atlantic Ocean from Massachusetts to Brazil & in the Gulf of Mexico.