 Of the major groups of teleosts , the <unk> , <unk> and <unk> ( perches , tunas and many others ) all have a worldwide distribution and are mainly marine ; the Ostariophysi and <unk> are worldwide but mainly freshwater , the latter mainly in the tropics ; the <unk> ( guppies , etc . ) have a worldwide distribution , both fresh and salt , but are surface @-@ dwellers . In contrast , the <unk> ( pikes ) are limited to freshwater in the Northern Hemisphere , while the <unk> ( salmon , trout ) are found in both Northern and Southern temperate zones in freshwater , some species migrating to and from the sea . The <unk> ( <unk> , etc . ) are Northern hemisphere fish , with both salt and freshwater species . 
