Small fish of the herring family (5)
I believe the answer is:
sprat
'small fish' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for sprat that I've seen before include "Type of herring - small person or thing" , "chap on a fat-free diet" , "Parts of a very small fish" , "Young herring" , "Small sea fish" .)