What structures are used by filter feeding fish in gathering food?

Answer 1

This is done in 2 stages:
1) Sucking in water: Done either by swimming through (baleen whales, krill, etc.) or by using tongue like piston (ducks, flamingoes, etc.)
2) Filtering mechanism: Baleen whales have huge baleen plates, which act like filter. Once the water is in, the tongue pushes water outside, and the food is strained while water is expelled. Birds and other filter feeding fishes have filter like projections as their mouth which allow them to push water alone outside while retaining the nourishment inside the mouth.