Some fish, like sharks, don’t posses an air bladder to help keep them afloat and must either swim continually or rest on the bottom.  

Fish have a specialized sense organ called the lateral line which works much like radar and helps them navigate in dark or murky water.

February 24, 2012 | Categories: From the Gremlin

Fish have a specialized sense organ called the lateral line which works much like radar and helps them navigate in dark or murky water.