alevins

An alevin is the larval stage of a fish after it has hatched from an egg, but still carries the yolk sac attached for nutrition. The term is commonly used for salmonids and other species with a similar development pattern. After fertilization, eggs develop in gravel nests or artificial incubators; when they hatch, the young fish remains immobile and relies on the yolk sac for nourishment.

During the alevin stage the animal does not feed externally. It stays relatively stationary, often remaining close to the gravel or substrate while the yolk sac is gradually absorbed. The length of this stage varies by species and environmental conditions, especially temperature. Once the yolk sac is depleted, the fish enters the next life stage, usually called the fry, and begins external feeding and more active swimming.

Alevins require clean, well-oxygenated water and suitable substrate to remain protected and to allow proper development. Environmental stress such as high siltation, low oxygen, or sudden temperature changes can reduce survival during this sensitive period. In hatcheries and aquaculture, alevins are kept in controlled tanks or troughs until the yolk sac is absorbed, after which they are moved to rearing systems for feeding and growth.

Ecologically, alevins represent an early recruitment stage in many fish populations. Their survival influences future populations, and protection of spawning sites, gravels, and early-life habitat is important for sustainable fisheries and conservation efforts. Related terms include embryo (before hatching) and fry (after yolk absorption).