The function of these bones is the same as in our species. It offers support to the body and sometimes protection for the organs (although this latter point varies considerably between fish species). They have no need to be as rigid and 'strong' as ours because the water they live in offers them support and a 'weightless' environment (as a scuba diver can experience). Bones can have bizarre uses in some species though, such as Pleurodeles waltl, the spanish ribbed newt, which forces it's ribs through its skin as a defence mechanism.