Fish I snared, all at sea (7)
I believe the answer is:
sardine
'fish' is the definition.
(sardine is a type of fish)
'i snared all at sea' is the wordplay.
'all at sea' indicates anagramming the letters.
'i'+'snared'='isnared'
'isnared' anagrammed gives 'SARDINE'.
(Other definitions for sardine that I've seen before include "Rinsed a (anag) - fish" , "Stonefish OR? Stone" , "A diner's small fish" , "Small pilchard" , "(Cramped?) fish" .)