Mostly minor, but there are some specific mosquito fish that the larvae make a sizeable contribution to the diet of and they're an important food source for dragonflies. That overall food would need to be found elsewhere though because they are a huge biomass. Also, as disease vectors they kill off a large number of animals. Without that culling there would be a population explosion at the top of the food chain and many of the middle creatures would go extinct from overpredation before the animals at the top started starving to death.