We didn't see any Mozzies during our 8 days in Fiji
There are mosquitoes, having a repellent ointment handy is recommended. Also there is a souvenir shop inside the hotel that sells insect repellent creams.
We were fine we just made sure before going out to all our repellent on in case
I didn't feel much but that's cuz with kids I am always carrying my repellent ... I always had repellent on the kids and myself and had no mosquitoe bites the entire two weeks in Fiji
Get an answer from Fiji Gateway Hotel staff and past guests.