Black and sticky but I've heard a second helping goes well with fish. (3)
I believe the answer is:
tar
'black' is the definition.
(I've seen this in other clues)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for tar that I've seen before include "Sticky substance used in road construction" , "Informal sailor, the rat" , "Product of coal" , "Black substance in cigarettes" , "Crewman" .)