Here is a general overview of how fish embryos feed using their yolk sac:
1. The yolk sac is formed from the nutrients stored in the egg during its development. It contains essential nutrients such as proteins, lipids, carbohydrates, and vitamins that are necessary for the growth and development of the embryo.
2. The developing fish embryo is directly connected to the yolk sac through specialised structures called vitelline vessels. These vessels are a network of blood vessels that transport nutrients from the yolk sac to the growing embryo.
3. As the embryo grows and develops, it begins to absorb nutrients from the yolk sac through the vitelline vessels. This absorption occurs via the process of pinocytosis, where small droplets of yolk material are engulfed by the cells of the vitelline vessels and internalised.
4. The nutrients from the yolk sac are then utilised by the embryo for its various metabolic processes, including the synthesis of proteins, the production of energy, and the development of tissues and organs.
5. The yolk sac serves as a temporary source of nutrition for the fish embryo during the early stages of its development. As the embryo matures and develops functional feeding structures, such as a mouth and a digestive system, it gradually transitions to external sources of food.
The utilisation of the yolk sac provides the necessary nourishment for the developing fish embryo before it can independently obtain food from the surrounding environment. Once the yolk sac is depleted, the embryo either hatches out of the egg and begins to feed externally or, in some cases, continues to receive nutrients from an attached yolk sac until it is fully developed.