Source : Webster's Revised Unabridged Dictionary (1913)

Soapfish \Soap"fish`\, n. (Zo["o]l.)
   Any serranoid fish of the genus {Rhypticus}; -- so called
   from the soapy feeling of its skin.

Source : WordNet®

soapfish
     n : fishes with slimy mucus-covered skin; found in the warm
         Atlantic coastal waters of America