How much energy do fish expend when floating "effortlessly" in the water column?

[SorellaLaBefana]

Turns out to be twice their requirement at rest

Fish make hanging motionless in the water column look effortless, and scientists had long assumed that this meant it was a type of rest. Now, a new study reveals that fish use nearly twice as much energy when hovering in place compared to resting...

...In particular, the scientists measured the physical separation between the fish's center of mass, which is determined by weight distribution, and its center of buoyancy, which is related to the shape and location of its swim bladder. All these measurements provided a way to quantify how stable or unstable each fish was...

"Hovering is a bit like trying to balance on a bicycle that's not moving," said Di Santo...

https://www.sciencedaily.com/releases/2025/07/250708045658.htm

The image used in the Science Daily article is of the Garibaldi Fish. This is the largest of the damselfish, and lives in Kelp Forests off the California coast. As divers know, such forests slow, but do not eliminate, currents so the fish pictured are likely also slowly swimming into the current besides hovering—as well as keeping an eye on the photographer!

The Monterey Bay Aquarium has a nice family-friendly discussion of the fish:
https://www.montereybayaquarium.org/animals/animals-a-to-z/garibaldi