In a wide, shallow bowl, beat together the egg and pineapple juice. Spread the flour and the coconut on separate plates, suitable for dredging.
Add 2-3 T vegetable oil to a saute pan set over medium heat.
Dry the fish fillets off as much as possible. Dredge first in the flour, then dip in egg and coat fish in coconut.
Working with 2-3 fillets at a time, add the fish to the pan. When coconut starts to brown, carefully turn over. When fish is cooked, remove from pan. Add more oil to pan if necessary and repeat with the remaining fish.