 Nursehounds are generally harmless to humans . However , 19th @-@ century British naturalist Jonathan Couch noted that " although not so formidable with its teeth as many other sharks , this fish is well able to defend itself from an enemy . When seized it throws its body round the arm that holds it , and by a contractile and reversed action of its body grates over the surface of its enemy with the rugged spines of its skin , like a rasp . There are few animals that can bear so severe an infliction , by which their surface is torn with lacerated wounds . " This shark is displayed by many public aquariums and has been bred in captivity . 
