Abstract
Oxygen uptake (MO2; mgO2 fish-1h-1) of fish groups was measured at temperatures between 10–19°C in an intermittent-flow respirometer to quantify the metabolic costs of spontaneous swimming patterns in the small clupeid Sprattus sprattus. Movements of individual fish within the school were tracked automatically during respirometry. Oxygen uptake was then related to mean swimming speeds and the number of sharp turns (>90°), which are common behavioural elements of spontaneous swimming in clupeid fish. Different possible model formulations for describing the relationship between respiration and swimming patterns were compared via the AIC. The final model revealed that costs for sharp turns at a frequency of 1 s-1 doubled the metabolic costs compared to those with zero turns but with likewise a moderate swimming speed of 0.28 body length -1. The cost for swimming doubled if the swimming speed was doubled from 0.28 to 0.56 BLs-1 but increased by a factor of 4.5 if tripled to 0.84 BLs-1. Costs for transport were minimal at a speed of 0.4 body lengths s-1 at all temperatures. New basic input parameters to estimate energy losses during spontaneous movements, which occur typically during foraging in this small pelagic fish, are provided.
Highlights
Fish swimming costs in bioenergetic models are often estimated from empirical relationships between oxygen uptake (MO2) and forced swimming speeds
We modelled the relationship between swimming speed (U) and oxygen uptake as a power function [36,37,38], which is based on hydrodynamic principles and allows for species comparisons when standard metabolic rate (SMR) is different [39,40]
Mean swimming speeds and the number of turns >90 ̊ per interval varied over time and resulted in variable oxygen uptake rates (Fig 2)
Summary
Fish swimming costs in bioenergetic models are often estimated from empirical relationships between oxygen uptake (MO2) and forced swimming speeds. Activity costs during spontaneous movements, may be larger and more variable than those of steady swimming [4,5,6] and variables other than average swimming speed can be important descriptors for estimating MO2 during spontaneous activity. For small pelagics, such as Sprattus sprattus (Linnaeus, 1758) or juvenile Clupea harengus (Linnaeus, 1758), spontaneous movements represent common behaviours during active feeding [7,8], searching for food or escaping from predators [9]. Planktivorous fishes may spend most of their time feeding continuously
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