The 30 plus species of cowfish and boxfish are unmistakable. Members of the family Ostracionidae lack pelvic fins and slowly cruise over the reef grazing upon algae and other encrusting organisms. In captivity, put them a well established aquarium with lots of algae and frequently feed them Romaine lettuce and mysis. They are not too competitive and are essentially defenseless, so place them into an aquarium with other slow feeding species. 

Acclimate them slowly and insure that there are no intakes for filters that are too rapid or equipment placed too close the glass as they may get stuck and become injured or die. Remove any stressed or dead specimens quickly, as they can exude a toxic compound that may kill other fish ( although this extremely rare and only documented in the Blue Boxfish from Hawaii). 

They are prone to Lymphocystis ( a usually harmless viral infection that looks like small warts, common on the fins), so keep the water clean to minimize chances of an outbreak. Despite all of the difficulties they are quite hardy as their slow movement make them easy to capture and hence they arrive in the fish store in good shape.

 Three genera are common to the hobby.

Lactoria The 4 horned cowfish is so named for the four conspicuous horns protruding from its trunk shaped body. Look closely at the horns and insure that they are fully sheathed and free from infection ( the horns are prime site for Lymphocystis). Their box shaped body hides the fact that their belly may be empty. If the eyes are shrunken or sullen, or if the fecal material is white and stringy, try to boost their diet with some blanched Romaine lettuce and lots of mysis (let them eat their fill). 

Ostracion  These are often called cubicus boxfish for they lack any prominent spines and are very "cuboidal" in shape. These species are very finicky and are among the species most likely to extrude ostracitoxin; a possible poison for other tank inhabitants. These delicate specimens are best kept in a non competitive reef aquarium. 

Lactophrys These cowfish resemble a composite of the above two. They are roughly cube shaped with small reduced horns and a prominent ridge running along their back. They are quite hardy, and share similar care to 4 horned cowfish to which they are closely related.