Dataset for: Inherent instability leads to high costs of hovering in near-neutrally buoyant fishes

Hovering, the ability to maintain a stationary position in fluid, is
essential for many fish species during prey capture, habitat exploration,
and mating. While traditionally assumed to be energetically inexpensive
for fishes with a swim bladder, the metabolic costs and morphological
factors influencing postural stability during hovering remain poorly
understood. Hovering requires fishes to counteract small instabilities in
position and orientation, often through continuous adjustments using their
fins and body. To examine the energetic consequences of this active
stabilization, we measured body posture, fin kinematics, and metabolic
rates in 13 near-neutrally buoyant fish species during both hovering and
resting. Our results show that hovering nearly doubles metabolic rates
compared to resting, and species with greater separation between the
center of mass and center of buoyancy and increased caudal fin activity
exhibit higher energetic costs. In contrast, species with more posteriorly
positioned pectoral fins and lower length-to-depth ratios show reduced
hovering costs. Our findings demonstrate that, despite morphological
traits that promote instability, fishes maintain posture and position
through fine-scale fin control—at a significant energetic expense. This
study suggests that hovering is a costly behavior that likely plays a key
role in shaping the evolution of fish morphology and locomotor strategies.