The provided diagram vividly illustrates the complex life cycle of the salmon, detailing its progression from an embryonic stage to full maturity. Overall, this biological process encompasses six distinct developmental phases and sees the salmon inhabit three primary environments: the freshwater river, the brackish estuary, and the vast ocean.
The cycle commences in the upper reaches of a river, where adult salmon deposit their eggs amongst the riverbed gravel. Following an incubation period, these eggs hatch into tiny alevins, which remain concealed within the gravel, sustained by their yolk sacs. Subsequently, these alevins develop into fry, emerging from their hiding places to feed and grow in the river’s freshwater environment.
The next critical stage involves the transformation of the fry into smolts, which then undertake a downstream migration from the river towards the estuary. Here, these young salmon undergo a vital adaptation to the changing salinity levels before eventually venturing out into the open ocean. They spend several years in the ocean, feeding and maturing into fully grown adults. Finally, driven by an innate instinct, these mature salmon embark on an arduous upstream journey back to their original freshwater spawning grounds in the river to reproduce, thereby completing the cycle and initiating a new generation.