title: Unsteady flow affects swimming energetics in a labriform fish (Cymatogaster aggregata).
abstract: Unsteady water flows are common in nature, yet the swimming performance of fishes is typically evaluated at constant, steady speeds in the laboratory. We examined how cyclic changes in water flow velocity affect the swimming performance and energetics of a labriform swimmer, the shiner surfperch, Cymatogaster aggregata, during station holding. Using intermittent-flow respirometry, we measured critical swimming speed (Ucrit), oxygen consumption rates (O2) and pectoral fin use in steady flow versus unsteady flows with either low- [0.5 body lengths (BL) s(-1)] or high-amplitude (1.0 BL s(-1)) velocity fluctuations, with a 5 s period. Individuals in low-amplitude unsteady flow performed as well as fish in steady flow. However, swimming costs in high-amplitude unsteady flow were on average 25.3% higher than in steady flow and 14.2% higher than estimated values obtained from simulations based on the non-linear relationship between swimming speed and oxygen consumption rate in steady flow. Time-averaged pectoral fin use (fin-beat frequency measured over 300 s) was similar among treatments. However, measures of instantaneous fin use (fin-beat period) and body movement in high-amplitude unsteady flow indicate that individuals with greater variation in the duration of their fin beats were better at holding station and consumed less oxygen than fish with low variation in fin-beat period. These results suggest that the costs of swimming in unsteady flows are context dependent in labriform swimmers, and may be influenced by individual differences in the ability of fishes to adjust their fin beats to the flow environment.
authors.affiliation: Australian Research Council Centre of Excellence for Coral Reef Studies, Research School of Biology, Australian National University, 116 Daley Road, Canberra, ACT 0200, Australia.
authors.forename: D G
authors.initials: DG
authors.lastname: Roche
authors.forename: M K
authors.initials: MK
authors.lastname: Taylor
authors.forename: S A
authors.initials: SA
authors.lastname: Binning
authors.forename: J L
authors.initials: JL
authors.lastname: Johansen
authors.forename: P
authors.initials: P
authors.lastname: Domenici
authors.forename: J F
authors.initials: JF
authors.lastname: Steffensen
mesh_terms: D058500:Animal Fins / Q000502:physiology; D000818:Animals; D001696:Biomechanical Phenomena; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D010473:Perciformes / Q000502:physiology*; D013550:Swimming
chemical_list: D010100:Oxygen
keywords: Complex flow; Critical swimming speed; Fin-beat frequency; Oxygen consumption rate; Pectoral fin swimming; Respirometry