They weigh small pieces of fish (6)
I believe the answer is:
scales
'pieces of fish' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
I also know that 'fish' relates to this answer.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for scales that I've seen before include "Justice should hold them evenly" , "Measuring instrument for weighing" , "Set of musical notes - balanced on a fish?" , "Weighing devices, sign of Libra" , "7 [SIGN OF THE ZODIAC] representative" .)