Stands while stuffing fish (6)
I believe the answer is:
easels
'stands' is the definition.
(I know this)
'while stuffing fish' is the wordplay.
'while' becomes 'as' (eg 'while I walked' means 'as I walked').
'stuffing' means one lot of letters goes inside another.
'fish' becomes 'eels' (eel is a type of fish).
'as' inserted inside 'eels' is 'EASELS'.
(Other definitions for easels that I've seen before include "Artists' tripods" , "Supports for paintings" , "Leases them out to artists" , "Painters' stands" , "Stands for artists' canvases" .)