Piece of bread, possibly to follow the fish (5)

I believe the answer is:

slice

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'piece of bread' is the definition.
(I've seen this in another clue)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for slice that I've seen before include "Piece (of cake?)" , "Piece cut from a larger portion" , "Spin" , "Portion of pizza" , "Cut into portions" .)

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