My fish wont eat. what do i do?

i got a japanese betta fish a few days ago and since i got it it havent been eating at all. its so weard i got a special betta food and the betta pellets and it wont eat. i thought maybe since i had it in a bowl it wouldnt eat so i brought a big tank where its really roomy with a filter(he seems pretty happy) but he still wont eat. what do i do? do i need another fish in the tank to keep him company? he seems pretty bored. his name is gills.