Note glue fixed to a whale (6)
I believe the answer is:
beluga
'whale' is the definition.
(I know that beluga is a type of dolphin)
'note glue fixed to a' is the wordplay.
'note' becomes 'b' (musical note).
'fixed' indicates an anagram.
'to' says to put letters next to each other.
'glue' with letters rearranged gives 'elug'.
'b'+'elug'+'a'='BELUGA'
(Other definitions for beluga that I've seen before include "Large Russian sturgeon" , "'Russian sturgeon, source of caviar (6)'" , "Species of sturgeon" , "Small white whale; type of caviar" , "fish" .)