Dries an alternative fish (7)
I believe the answer is:
sardine
'fish' is the definition.
(sardine is a type of fish)
'dries an alternative' is the wordplay.
'alternative' is an anagram indicator (an alternative ordering of the letters).
'dries'+'an'='driesan'
'driesan' with letters rearranged gives 'SARDINE'.
(Other definitions for sardine that I've seen before include "(Cramped?) fish" , "Swimmer" , "A diner's small fish" , "Fish in tin?" , "Fish (often tinned)" .)