三文鱼的生命周期Life cycle of a fish called the salmon

The diagrams illustrate the life cycle of the salmon, a large fish species that undergoes three major stages of development in distinct aquatic environments, namely: river, estuary, and open ocean. Overall, salmon progress from eggs laid in slow-moving upper-river streams to mature adults living in the ocean before eventually returning to their place of origin to reproduce, and the whole process takes approximately 9 years. The cycle is characterised by changes in size, habitat and behaviour. As the diagram suggests, the lifecycle of salmon begins in the upper reaches of rivers, where eggs are deposited among small stones and reeds. After roughly five to six months, the eggs hatch into fry, which are small fish of approximately 3 to 8 centimetres in length. At this stage, they gradually migrate downstream, where the current is fast-flowing. As the fry grow into smolt, typically reaching a size of 12 to 15 centimetres, they move into the estuary. This transitional environment allows them to adapt to saltwater conditions. They spend a period of maturation here before entering the open sea. In the ocean, salmon reach full adulthood, growing significantly larger, often around 70 to 76 centimetres. They remain in this habitat for approximately 5 years, feeding and developing the energy reserves needed for their return journey. Eventually, the mature adults swim back upstream to the calm freshwater environment where they originally hatched, completing the cycle by laying eggs and restarting the process.