it is part of the cycle of fish
starts with Alevin (The life stage of a fish when the yolk sac is still present) then moves to fry (May be applied to any small fish, but generally fish are termed fry up to a size of 5-10grams) then to Fingerling (typically between approximately 10 and 40 grams. Often used up to 1 year of age for some species)
after that they are adult fish or just plain fish