DOI: 10.5061/dryad.9cnp5hqw7
title: Dataset for: Inherent instability leads to high costs of hovering in near-neutrally buoyant fishes

description: 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.
description: # Dataset for: Inherent instability leads to high costs of hovering in
 near-neutrally buoyant fishes Dataset DOI:
 [10.5061/dryad.9cnp5hqw7](10.5061/dryad.9cnp5hqw7) ## Description of the
 data and file structure This dataset supports the manuscript
 "Inherent instability leads to high costs of hovering in
 near-neutrally buoyant fishes," by Di Santo et al., which
 investigates the energetic and biomechanical costs of hovering across 13
 species of near-neutrally buoyant fishes. Experimental Overview: Data were
 collected using a combination of respirometry, high-speed video, and
 morphometric analysis. Fish were placed in flow tanks where their oxygen
 consumption was measured during rest and while hovering. Simultaneously,
 body posture and fin movements were recorded and analyzed with high-speed
 cameras. Morphological measurements were used to estimate the spatial
 relationship between the center of mass (COM) and the center of buoyancy
 (COB), as well as to calculate fin positions and body shape parameters.
 ### Files and variables \- MO2 hovering.txt: Individual-level oxygen
 consumption measurements (resting, hovering, net metabolic rate), and MO₂
 hover/rest ratios. \- hovering morphology.txt: Morphological data
 including COM–COB separation, body shape ratios, mass, and size metrics.
 \- hovering body posture.txt: Body angle, roll, pitch, and curvature
 metrics during hovering trials. \- hovering fin position.txt: Normalized
 pectoral and caudal fin positions along the body axis. \- hovering
 kinematics.txt: distance traveled by fins during hovering. **Column
 headers explanation:**  ### **MO2_hovering.txt:** * species: Species'
 scientific name. * common name: Common name of the species. * Fish ID:
 Identifier for each individual fish tested. * Mass (Kg): Mass of the fish
 in kilograms. * MO2 value: Oxygen consumption (MO₂) rate measured in mg
 O₂/kg/h. * MO2 type: Type of oxygen consumption measurement (hovering,
 resting, net [=hovering-rest], or hovering/resting ratio). ###
 **hovering_morphology.txt:** * Species: Species' scientific name. *
 COM-COB ant/post: Anterior/posterior distance (negative values indicate
 COM anterior to COB; positive values indicate COM posterior to COB).
 Values as proportion of body length. * COM-COB dorsal/ventral:
 Dorsal/ventral distance (negative values indicate COM dorsal to COB;
 positive values indicate COM ventral to COB). Values as proportion of body
 depth. * TL-Width Ratio: Ratio of total length to body width. * fineness
 ratio (tl-width): Hydrodynamic shape ratio calculated as total length
 divided by body width. * TL: Total length of the fish (cm). * Width:
 Maximum width of the fish (cm). * depth: Maximum depth (height) of the
 fish (cm). * fineness ratio depth: Hydrodynamic shape ratio calculated as
 total length divided by body depth. * mass: Body mass of the fish (g). *
 Kj per 10 min: Energy expenditure in kilojoules per 10 minutes during
 hovering. ### **hovering_body_posture.txt:** * Species: Species'
 scientific name. * Fish: Individual fish identifier. * BODY angle: Body
 angle relative to horizontal (degrees). * Roll angle: Degree of lateral
 rotation about the body axis (degrees). * Pitch angle: Degree of vertical
 rotation about the lateral axis (degrees). * curvature: Degree of
 curvature of the fish’s body during hovering. ###
 **hovering_fin_position.txt:** * common name: Common name of the species.
 * Species: Species' scientific name. * pectoral_start /BL: Starting
 position of the pectoral fin normalized by body length (BL). *
 caudal_start /BL: Starting position of the caudal fin normalized by body
 length (BL). ### **hovering_kinematics.txt:** * Species: Species'
 scientific name. * Filename: Original data file for high-speed video
 tracking. * Number of frames: Total number of video frames analyzed. * TL:
 Total length of fish (cm). * Pectoral fin base: Distance traveled by the
 base of pectoral fin (cm). * Pectoral fin tip: Distance traveled by the
 tip of pectoral fin (cm). * Pectoral fin tip offset: Lateral offset
 movement of pectoral fin tip (cm). * Snout, Eye, Dorsal, Anal, Pelvic L,
 Pelvic R, Peduncle, Caudal: Distance traveled by respective anatomical
 landmarks (cm). * Caudal offset: Lateral offset movement of caudal fin
 (cm). * Lat: Side (L or R) predominantly active or tracked. * Bin: Binary
 indicator used for data categorization (e.g., 0 or 1). * Blank cell: N/A
 ## Code/software n/a