Crayfish in sea - no glut, unfortunately (9)
I believe the answer is:
'crayfish' is the definition.
('langouste' can be a synonym of 'crayfish')
'sea no glut unfortunately' is the wordplay.
'unfortunately' indicates anagramming the letters.
'seanoglut' anagrammed gives 'LANGOUSTE'.
'in' acts as a link.
(Other definitions for langouste that I've seen before include "Shellfish" , "something to eat" , "One in the sea" , "It may be eaten roasted" , "Crayfish" .)