Otters eat mostly small, slow-moving fish. North American river otters target species in the 4- to 6-inch range, including carp, mud minnows, sticklebacks, and suckers. But the full picture depends on the type of otter and where it lives, because the 13 otter species around the world have adapted to very different waterways and prey.
North American River Otters
River otters in North America are opportunistic feeders, but the bulk of their diet is non-game fish. They prefer slow-moving species they can easily catch in shallow water: carp, suckers, mud minnows, and sticklebacks. These are not the trout and bass that anglers worry about. Studies consistently show that river otters rarely make a dent in sport fish populations, despite their reputation.
The major exception is salmon. River otters actively seek out spawning runs and will travel significant distances to reach them. When salmon are packing into rivers to spawn, otters take full advantage of the concentrated, energy-rich prey. Outside of spawning season, though, they stick to whatever small, abundant fish are easiest to catch.
River otters eat 15% to 20% of their body weight every day. For a typical 20-pound otter, that’s 3 to 4 pounds of food daily, most of it fish. Their high metabolic rate, which helps them stay warm in cold water, drives this constant need to eat.
European Otters
Eurasian otters show a remarkably similar pattern to their North American cousins. Research across multiple European habitat types found that over 80% of the fish otters consumed weighed less than 100 grams (about 3.5 ounces). They overwhelmingly target what biologists call eurytopic fish, species that tolerate a wide range of environmental conditions and tend to be common and widespread.
Habitat shapes which fish end up on the menu. Otters living along rivers eat more fast-water species, while otters near ponds and marshes eat more still-water fish. Across all habitats, though, the preference leans toward slower, more abundant species. Invasive and non-native fish also made up a significant portion of the diet in studies across the Pannonian region of central Europe.
European otters do take economically important fish when available. In two Norwegian rivers, researchers tracked radio-tagged Atlantic salmon and found that otters killed 32% of adult salmon in one river and 95% in another. The difference came down to habitat: the river with more deep holding pools gave salmon places to hide, which dramatically reduced predation. Notably, the otters didn’t pick and choose. They showed no preference for larger fish, males over females, or weaker individuals. They simply caught whatever salmon they could.
Asian Small-Clawed Otters
The world’s smallest otter species breaks the pattern. Asian small-clawed otters are primarily invertebrate eaters, with crabs making up about 41% of their diet and snails another 22%. Fish account for only about 19% of what they eat.
When they do eat fish, they favor species that live in shallow, weedy water. In peat swamp forests of southern Thailand, the most common fish in their diet were three-spot gouramis (about 49% of fish consumed) and climbing perch (about 22%). Both are tough, air-breathing fish that live in slow or stagnant water, exactly the kind of shallow habitat where small-clawed otters forage with their sensitive, dexterous paws. Walking catfish, swamp eels, and snakeheads round out the list, all of them bottom-dwelling or slow-water species.
Their fish preferences also shift with the seasons. During the wet season, climbing perch dominated at about 35% of fish eaten. In the dry season, three-spot gouramis surged to 65%, likely because shrinking water levels concentrated these fish into smaller pools where they were easier to catch.
Sea Otters
Sea otters are the outlier in the otter world. They live entirely in marine environments along the Pacific coast and eat very little fish compared to their freshwater relatives. Their diet centers on sea urchins, crabs, clams, mussels, and abalone. When they do eat fish, it’s typically slow-moving bottom species rather than open-water swimmers. Sea otters need even more food than river otters, consuming 25% to 30% of their body weight daily to compensate for heat loss in cold ocean water.
Why Otters Prefer Small, Slow Fish
A clear pattern runs through every otter species: they eat the fish that are easiest to catch. Small body size, slow swimming speed, and life in shallow or still water all make a fish more likely to end up as otter prey. This isn’t laziness. It’s energy economics. Chasing a fast trout through open water burns calories that a 4-inch sucker caught in the shallows does not.
This preference means otters naturally gravitate toward the most common, least prized fish in any waterway. The species they eat most heavily tend to be abundant, fast-reproducing, and ecologically resilient. In many cases, otters actually help control populations of invasive or overabundant small fish, which can benefit the broader ecosystem. The fear that otters decimate sport fish populations is largely unsupported by dietary studies, with the notable exception of salmon during spawning runs, when the fish are concentrated, exhausted, and unusually vulnerable.