Sandier sort of fish (7)
I believe the answer is:
sardine
'fish' is the definition.
(sardine is a type of fish)
'sandier sort' is the wordplay.
'sort' indicates anagramming the letters.
'sandier' with letters rearranged gives 'SARDINE'.
'of' is the link.
(Other definitions for sardine that I've seen before include "FRENCH FISH" , "Small fish, usually canned" , "Fish (often tinned)" , "Stonefish OR? Stone" , "Small pilchard" .)