Many fish species have larvae that live in the plankton for some time, including bottom dwelling fish species such as flatfish. Often the larva looks completely different from the adult fish. In the beginning, flatfish larvae look like an ordinary fish, with eyes on both sides of the body. Only later one eye moves to the other side of the body.
Fish often produce enormous amounts of eggs that are discharged into the open water, or attached to the bottom like in herring. Fish larvae still live on nutrients in the yolk sac at the beginning of their lives, but when they run out of them they start looking for food themselves, usually this is zooplankton.
Fish larvae such as horse mackerel and whiting often hang around jellyfish as protection against predators.