Fry

Fry are the earliest free-swimming juvenile fish, spanning from complete yolk-sac absorption (when the fish must begin exogenous feeding) up to roughly 2–3 cm or a few grams, before they graduate to the fingerling stage. This is the most mortality-prone phase of the entire production cycle: larvae transition from endogenous yolk to capturing live prey, their gills and digestive tract are still differentiating, and their immune system is functionally naive, so typical survival from first feeding to fry is only 30–70% even in professional hatcheries. First-feeding diets are decisive — marine larvae generally require live prey such as rotifers (for 5–15 days) followed by Artemia nauplii, while freshwater species like tilapia and carp can often be started directly on fine crumble — and water quality must be held tight (temperature ±0.5°C, ammonia near zero, gentle hydrodynamics). Fry are counted volumetrically or by sample weighing and stocked into nursery tanks at densities that fall daily as they grow. For the hatchery operator, fry-stage management — feeding regime, grading, and sanitation — determines how many healthy fingerlings a facility can sell; losses here cannot be recovered later. Fry connects hatchery, larviculture, live-feed, and fingerling into the sequential early rearing chain.