 Nursehounds have nocturnal habits and generally hide inside small holes during the day , often associating with other members of its species . A benthic predator , it feeds on a range of bony fishes , smaller sharks , crustaceans , and cephalopods . Like other catsharks , the nursehound is oviparous in reproduction . Females deposit large , thick @-@ walled egg cases , two at a time , from March to October , securing them to bunches of seaweed . The eggs take 7 – 12 months to hatch . Nursehounds are marketed as food in several European countries under various names , including " flake " , " catfish " , " rock eel " , and " rock salmon " . It was once also valued for its rough skin ( called " rubskin " ) , which was used as an abrasive . The International Union for Conservation of Nature ( IUCN ) has assessed the nursehound as Near Threatened , as its population in the Mediterranean Sea seems to have declined substantially from overfishing . 
