Salmon are anadromous fish, known for their lengthy migrations between freshwater and marine environments. Minnows are small, common freshwater fish that inhabit the same rivers and lakes where salmon begin and end their lives. While the salmon’s diet changes drastically throughout its life, they do consume minnows, but only under specific circumstances related to their age and location. This consumption is primarily seen in freshwater habitats.
Minnows as an Opportunistic Food Source
The consumption of minnows by salmon is primarily an opportunistic event that occurs in freshwater. Juvenile salmon, known as parr, will feed on small fish like minnows and sticklebacks once they reach a size that allows them to successfully hunt this type of prey. Fish become an increasingly important part of the diet for young salmon once they grow to about 12 inches in length.
For landlocked salmon populations, which complete their entire life cycle without migrating to the ocean, minnows and other small forage fish are a regular component of their adult diet. These salmon rely heavily on available baitfish in the lakes they inhabit, although their preferred and most common forage species is often the rainbow smelt. Minnows are consumed when they are abundant and easily captured, providing a quick source of energy.
If a minnow or similar small fish is present and represents an easy meal, the salmon will take it. Anglers frequently use minnows as bait or use lures that resemble them, confirming that salmon readily strike small fish in their freshwater habitat.
Diet Shifts Across Life Stages
The salmon’s life cycle involves a profound shift in diet as they transition from their natal freshwater streams to the vast open ocean. In their earliest stages, known as fry and parr, salmon predominantly feed on tiny aquatic organisms, including zooplankton, insect larvae, and smaller crustaceans like amphipods. This invertebrate-heavy diet sustains them during the first one to three years they spend in the river environment.
Once the salmon transform into smolts and migrate to the ocean, their diet changes to reflect the available marine prey. The calorie-rich ocean environment allows them to grow rapidly by consuming pelagic schooling fish, such as herring, sand lance, and capelin. They also eat larger crustaceans, notably krill, and cephalopods like squid.
The shift to the ocean means the consumption of minnows ceases, as minnows are strictly freshwater species. The larger, more energy-dense marine prey items are necessary to fuel the salmon’s massive growth phase. Upon returning to their natal river to spawn, most salmon stop feeding entirely, relying instead on stored fat reserves for the final migration.
General Foraging Behavior
Salmon are highly effective predators whose hunting strategy is largely visual, positioning them as sight-feeders. They use their keen eyesight to target moving prey, which is why bright, flashing lures that mimic small baitfish are often successful. Their hunting is most aggressive when they are actively building up energy stores, such as during their time in the ocean or in the spring when landlocked populations are feeding.
The overall strategy is governed by prey selectivity, where the salmon choose meals that offer the greatest energy return for the least effort. This means they will often select for easy-to-catch, energy-rich prey. For example, some Pacific salmon species show a preference for larger fish with higher lipid content, such as Chinook salmon.
When a salmon encounters a minnow in a river, the decision to consume it fits this high-reward strategy. The minnow is a relatively large, protein-dense meal compared to an insect larva. However, the salmon’s instinctual drive to strike a small, moving object can sometimes be mistaken for active feeding, particularly among spawning adults who are physiologically programmed to fast but may still strike at a passing minnow out of territoriality or reflex.