A monumental study of fish in the Barents Sea has revealed a fascinating truth: most of them don’t eat much. Scientists from Norway and Russia studied stomach contents from 27,000 fish, covering 70 different species.
The pattern was striking. One third of the fish had empty stomachs, many had just a little food, and only a handful were truly full.
“Fish eat what they need to balance their energy, and usually that means a small daily ration,” says marine researcher Hein Rune Skjoldal. “They also have to weigh the risk of being eaten themselves. Once their needs are met, more food is not a priority.”
A Few Exceptions
There are exceptions to the broader ocean. In tropical seas lives the black swallower, a deep-sea fish famous for gulping down prey ten times its own body weight.
But in the Barents Sea, the rule is moderation. On average, fish stomachs weighed only 2 per cent of body mass. The record was 34 per cent, but such cases were rare.
Who Eats Less, Who Eats More?
The researchers found unmistakable differences between species. Greenland halibut and long rough dab had the highest share of empty stomachs—72 per cent and 58 per cent, respectively.
Cod and haddock were at the other end, with only 22 and 24 per cent empty. The cause may be linked to growth speed and digestion. Cod, for example, grows fast and needs more regular meals.
The study also showed more plankton than bottom-living prey in the fish stomachs. That suggests that fast-growing, plankton-eating fish need more regular feeding. At the same time, slow-growing species that feed on worms or shellfish can go longer between meals.
A Window Into Climate Change
The project is part of a long-running Norwegian–Russian collaboration. Most of the samples came from the “Year of the Stomach” expeditions in 2015.
By studying what fish eat, scientists get insight into the whole ecosystem. If future surveys show changes in diet, it could signal broader shifts.
“The northern Barents Sea is moving from an Arctic to an Atlantic climate,” Skjoldal explains. “Some species will thrive, others will struggle. Stomach data helps us see these changes early.”