Stands when covered in fish (6)
I believe the answer is:
easels
'stands' is the definition.
(artists' stands)
'when covered in fish' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'covered in' means one lot of letters goes inside another.
'fish' becomes 'eels' (eel is a type of fish).
'as' placed inside 'eels' is 'EASELS'.
(Other definitions for easels that I've seen before include "Supports for paintings" , "Artists' tripods" , "Stands for blackboards, artists' paintings etc" , "Supports in the studio" , "Stands for artists' canvases" .)