Starts using gum in fish eggs for blusher (5)
I believe the answer is:
rouge
'for blusher' is the definition.
(synonyms)
'starts using gum in fish eggs' is the wordplay.
'starts' suggests taking the first letters.
'in' is an insertion indicator.
'fish eggs' becomes 'roe' (synonyms).
The first letters of 'using gum' is 'ug'.
'ug' inserted within 'roe' is 'ROUGE'.
(Other definitions for rouge that I've seen before include "Face-reddening cosmetic" , "Make-up item" , "Ferric oxide powder" , "Reddish cosmetic for colouring cheeks" , "Powder for the cheeks" .)