Salad of tuna and rice not initially dubious (9)
I believe the answer is:
uncertain
'dubious' is the definition.
('uncertain' can be similar in meaning to 'dubious')
'salad of tuna and rice not initially' is the wordplay.
'salad of' indicates anagramming the letters.
'and' says to put letters next to each other (I've seen this in other clues).
'initially' suggests taking the first letters.
The initial letter of 'not' is 'n'.
'tuna' put after 'rice' is 'ricetuna'.
'ricetuna' is an anagram of 'uncertai'.
'uncertai'+'n'='UNCERTAIN'
(Other definitions for uncertain that I've seen before include "in the lap of the gods" , "Not definitely known" , "Not at all sure or decided" , "up in the air" , "Unsure" .)