Cram leek roughly into fish (8)
I believe the answer is:
mackerel
'fish' is the definition.
(mackerel is a kind of fish)
'cram leek roughly' is the wordplay.
'roughly' indicates an anagram.
'cram'+'leek'='cramleek'
'cramleek' with letters rearranged gives 'MACKEREL'.
'into' is the link.
(Other definitions for mackerel that I've seen before include "Sea fish" , "Sea-fish" , "Food fish related to tuna" , "Small stripped fish, very tasty" , "Important food fish" .)