Something swimming in garlic, oddly (3)
I believe the answer is:
cod
'something swimming' is the definition.
(cod is a kind of fish)
'in garlic oddly' is the wordplay.
'in' indicates a hidden word.
'COD' is hidden within 'garlic oddly'.
(Other definitions for cod that I've seen before include "A foolish sort of a fish" , "to be paid for when it arrives" , "A joke of a fish?" , "Fish noted for liver oil" , "A white fish" .)