Fish and clam reek terribly (8)
I believe the answer is:
mackerel
'fish' is the definition.
(mackerel is a kind of fish)
'clam reek terribly' is the wordplay.
'terribly' indicates an anagram.
'clam'+'reek'='clamreek'
'clamreek' is an anagram of 'MACKEREL'.
'and' is the link.
(Other definitions for mackerel that I've seen before include "Commonly-eaten fish" , "Banded food fish" , "Common striped fish, very tasty" , "Food fish with a blue-green back" , "Marine food fish" .)