Roe source (4)
'roe source' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for shad that I've seen before include "fish that's been caught" , "Herring-like fish" , "Fish related to the herring" , "Fish; dash (anag.)" .)
(Other definitions for smelt that I've seen before include "half a guinea" , "was whiffy" , "18 [EXTRACT] metal" , "Small silvery fish" , "Extract (metal) from ore by heat" .)