Alevin

Juvenile fish go through various stages between birth and adulthood. They start as eggs which hatch into larvae. The larvae are not able to feed themselves, and carry a yolk-sac which provides their nutrition. Before the yolk-sac completely disappears, the tiny fish must become capable of feeding themselves. When they have developed to the point where they are capable of feeding themselves, the fish are called fry. When, in addition, they have developed scales and working fins, the transition to a juvenile fish is complete and it is called a fingerling. Fingerlings are typically about the size of fingers. The juvenile stage lasts until the fish is fully grown, sexually mature and interacting with other adult fish.

Ichthyoplankton (planktonic or drifting fish) are the eggs and larvae of fish. They are usually found in the sunlit zone of the water column, less than 200 metres deep, sometimes called the epipelagic or photic zone. Ichthyoplankton are planktonic, meaning they cannot swim effectively under their own power, but must drift with ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into juveniles. Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals.

According to Kendall et al. 1984 there are three main developmental stages of fish:

This article is about the juvenile stage.

Fry and fingerling are terms that can be applied to juvenile fish of most species. But some groups of fishes have juvenile development stages particular to the group. This section details the stages and the particular names used for juvenile salmon.

Salmon eggs. The growing larvae can be seen through the transparent egg envelope. The black spots are the eyes.

Salmon egg hatching into a sac fry. In a few days, the sac fry will absorb the yolk sac and become a salmon fry

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