The diagrams illustrate the life cycle of the salmon, a notable species of large fish, delineating its progression through various developmental stages.
The life cycle encompasses four primary stages: egg, fry, smolt, and adult salmon, with significant transitions occurring both in freshwater environments and in the open sea.
Initially, the salmon eggs are deposited in a gravel bed among stones within the upper reaches of the river, characterized by slow currents. This incubation phase lasts approximately 5 to 6 months, culminating in the emergence of fry, which range in size from 3 to 8 centimeters. At this fry stage, they inhabit the upper river region, accompanied by aquatic vegetation and environmental features like fallen trees and reeds. Subsequently, the fry migrate to the lower river, which is identified as a fast-flowing habitat, where they continue to develop over the course of about one year, growing to lengths of 11 to 15 centimeters, at which point they are classified as smolts.
The smolt stage is a critical transitional period that lasts for approximately one year before these fish embark on their migratory journey to the ocean. Upon arrival in the saline waters, the salmon undergo further growth, reaching substantial sizes of 70 to 76 centimeters within a timeframe of about four years. During this period, they mature into adult salmon, capitalizing on the nutrient-rich marine environment. Following their development, the adult salmon undertake a remarkable upstream migration to return to their natal river, where they engage in spawning, thereby completing their life cycle and initiating the sequence anew.
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