Alevins are the early life stage of fish, particularly those that hatch from eggs. They are typically very small and still carry a yolk sac, which provides them with nutrients until they are ready to swim and feed on their own. This stage is crucial for their development and survival in aquatic environments. During the alevin stage, fish are vulnerable to predators and environmental changes. They usually remain close to the substrate, where they can find shelter. As they grow and absorb the yolk sac, they transition into the next stage called fry, where they begin to actively swim and search for food.