Yes, many fish species eat jellyfish, and they do so far more often than scientists once believed. For decades, jellyfish were dismissed as nutritional dead ends in the ocean food web, too watery and low in calories to be worth eating. But newer methods like DNA analysis of gut contents and underwater cameras have revealed that a surprisingly wide range of fish, from salmon to deep-sea wolffish, regularly feed on jellyfish as part of their diet.
Which Fish Eat Jellyfish
The list of confirmed jellyfish-eating fish is longer than most people expect. Ocean sunfish are the most famous example, but chum salmon, grey triggerfish, greater silver smelt, and northern wolffish all consume significant amounts of jellyfish. Chum salmon stand out among their relatives. While most salmon species ignore jellyfish, chums actively move toward swarms of them and feed. Their diet can shift from primarily small crustaceans to primarily gelatinous prey depending on what’s available.
In deeper waters off Greenland, researchers found that northern wolffish stomachs contained enormous quantities of a deep-sea jellyfish called Atolla, with jellyfish DNA making up over half of all prey detected. Greater silver smelt showed the highest frequency of jellyfish in their stomachs among all deep-sea species studied, feeding heavily on a type of colonial jellyfish relative called a siphonophore. These aren’t occasional snacks. For some species, jellyfish form a core part of the diet.
The Ocean Sunfish Myth
Ocean sunfish have a reputation as dedicated jellyfish specialists, but the reality is more nuanced. A DNA barcoding study of sunfish diets found that jellyfish made up only about 16% of their overall prey. Small sunfish (under about 16 inches) ate mostly crustaceans and other fish, with jellyfish accounting for just 7% of their diet. As sunfish grow larger, though, jellyfish become increasingly important. The biggest sunfish studied, over about 32 inches, had diets where jellyfish-related prey made up roughly 57% of consumed items. So the stereotype is partially right, but only for larger, more mature sunfish. Younger ones eat a far more varied diet.
Why Fish Eat Something That’s 95% Water
Jellyfish are roughly 95% water by weight, which makes them seem like a terrible meal. But on a dry weight basis, they’re actually 20% to 54% protein and rich in minerals. Fat content is negligible, and calorie density is low (1 to 5 calories per gram of dry weight). About half of their protein is collagen. So while a fish has to eat a large volume of jellyfish to get meaningful nutrition, what’s there isn’t empty.
Several factors make jellyfish worth the effort despite their watery composition. They’re easy to catch compared to fast-swimming prey. They often appear in massive, dense blooms that concentrate food in one place. They digest rapidly in a predator’s stomach, meaning a fish can eat them continuously without feeling full for long. And perhaps most importantly, fish don’t eat jellyfish indiscriminately.
Fish Target the Best Parts
Research on a small Mediterranean fish called the bogue revealed that fish can be remarkably selective about which parts of a jellyfish they eat. During spring and summer, bogues specifically targeted the reproductive organs (gonads) of jellyfish, which contain six times more energy than the watery body tissue due to higher concentrations of fat and protein. They even showed a preference for female jellyfish, whose gonads had significantly more energy than male gonads because of their higher fat content.
During the rest of the year, when jellyfish gonads were less developed, the fish switched to less-selective feeding on whatever jellyfish tissue was available. This kind of strategic feeding means the caloric return from eating jellyfish is much higher than you’d estimate by looking at the nutritional content of the whole animal. Predators are cherry-picking the nutrient-dense parts.
Juvenile Fish Living Inside Their Food
One of the stranger relationships between fish and jellyfish involves young fish that actually shelter beneath jellyfish bells, hiding among the tentacles for protection from predators. Many of these juvenile fish don’t just use jellyfish as a hiding spot. They eat them too. Young Atlantic bumper, a small fish found in the Atlantic Ocean, feed directly on their jellyfish hosts, and stable isotope analysis has shown that jellyfish can make up 100% of their diet during this life stage.
Scientists have described this arrangement as a “gingerbread house hypothesis,” a reference to the fairy tale where a house is made of food. The juvenile fish get both shelter and a meal from the same organism. They may also feed on tiny crustaceans that parasitize the jellyfish, or on zooplankton swept up by the jellyfish’s swimming pulses. This dual benefit of protection and nutrition likely gives these young fish a significant survival advantage during their most vulnerable life stage.
Jellyfish Are Not Dead Ends
The old view that jellyfish are “trophic dead ends,” organisms that absorb energy from the food web but don’t pass it back up to larger predators, is now considered outdated. Advances in DNA metabarcoding (analyzing DNA fragments in stomach contents and fecal samples) have shown that jellyfish are consumed by a far wider range of animals than direct observation suggested. Fish, seabirds like fulmars and albatross, sea turtles, penguins, eels, octopus, crabs, and sea cucumbers all feed on them.
The reason earlier studies underestimated jellyfish predation is straightforward: jellyfish dissolve quickly in a predator’s stomach. Traditional methods of identifying prey by looking at stomach contents under a microscope missed jellyfish because they’d already been digested beyond recognition. DNA-based methods can detect jellyfish remains even after they’ve broken down into an unrecognizable slurry. With these tools, the picture has shifted dramatically. Jellyfish blooms represent a massive, seasonally available food source, and marine predators from the surface to depths of over a mile are taking advantage of it.