All fish with fins and easily removable scales may be eaten. (Leviticus Ch.XI,9).  It is important to note that only cycloid and ctenoid scales meet the Halachic definition of easily removable scales and all other forms of water-life including Eels, Crabs and Shellfish are treifeh.  

Minced fish should only be brought from kosher fish shops or should be minced at home.  See “Fish in the directory”.