Salmon are migratory fish that undergo remarkable transformations throughout their lives, a journey that profoundly influences their dietary needs and feeding behaviors. Their diet adapts considerably as they mature and move between freshwater and marine environments, or when raised in aquaculture settings. Understanding these dietary differences provides insight into their biology and the characteristics of the salmon consumed by humans.
Wild Salmon: Freshwater Diet
Young wild salmon begin their lives in freshwater rivers, streams, and lakes, where their diet consists of smaller, readily available prey. These juvenile salmon, known as fry and parr, become active hunters. Their primary food sources include a variety of aquatic invertebrates. This often includes microscopic animals like zooplankton, small shrimp-like crustaceans such as amphipods, and the larvae of various insects like caddisflies, blackflies, mayflies, and stoneflies.
Wild Salmon: Oceanic Diet
Upon reaching the smolt stage, salmon migrate to the ocean, where their diet shifts dramatically. Wild salmon transition to consuming larger and more diverse prey. Their diet in the ocean commonly includes smaller fish species like capelin, herring, sand lance, barracudina, lanternfish, blue whiting, and sandeel. They also feed on various crustaceans, such as euphausiids (krill) and amphipods, along with cephalopods like squid and octopus. This abundant and varied diet in the ocean supports their rapid growth and maturation.
Farmed Salmon: Controlled Nutrition
Farmed salmon receive a highly controlled diet delivered through specially formulated pellets. These pellets are designed to meet the salmon’s precise nutritional requirements at each life stage. The main ingredients typically include marine raw materials such as fish meal and fish oil. Plant-based ingredients, including proteins from soy, corn, rapeseed, wheat, broad beans, and sunflowers, constitute a significant portion, sometimes up to 70 percent of the feed. The pellets also contain essential vitamins, minerals, and pigments to support the salmon’s health and appearance.
Why Salmon’s Diet Matters
The diet of salmon, whether wild or farmed, significantly influences their growth, physical characteristics, and nutritional composition. The distinctive pink or orange color of salmon flesh comes from carotenoids, particularly astaxanthin. Wild salmon acquire astaxanthin naturally by consuming crustaceans like krill, while farmed salmon receive it as an additive in their feed. This pigment functions as an antioxidant and is important for the salmon’s metabolism, muscle function, and immune system.
Dietary composition also impacts the fat content and muscle development of salmon. Farmed salmon tend to have a higher fat content in their muscle tissue compared to wild salmon. This can lead to differences in taste and texture, with farmed salmon generally having a milder flavor and softer texture, while wild salmon may have a bolder, more pronounced taste and leaner flesh. Both wild and farmed salmon are valuable sources of omega-3 fatty acids, essential vitamins like B vitamins and vitamin D, and minerals such as selenium and phosphorus.