Sailor catches large fish (7)
I believe the answer is:
bloater
'fish' is the definition.
(bloater is a kind of fish)
'sailor catches large' is the wordplay.
I cannot quite understand how this works, but
'large' could be 'l' (eg in clothes sizes) and 'l' is found in the answer.
'sailor' could be 'boater' (synonyms) and 'boater' is located in the remaining letters.
No letters remain.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for bloater that I've seen before include "Fish" , "Something fishy" , "Herring salted and smoked" , "Cured herring" , "that will more than fill one up" .)