Gold fish eat newt eggs and larvae, koi eat newt eggs, larvae, and adults, and they often destroy the plants that newts lay their eggs on. Newts leave the water in the winter and go into piles of leaves, under rocks, and under logs where the temperatures are slightly warmer than their surroundings, though not much. They hibernate on land until spring comes, when they go back to the ponds. If you've had newt success, with fish in your pond this year I don't see why it won't happen next year, but usually newts never come to ponds with fish in the first place.