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Link to original content: http://pubmed.ncbi.nlm.nih.gov/32843970/
Bidirectional cyclical flows increase energetic costs of station holding for a labriform swimming fish, Cymatogaster aggregata - PubMed Skip to main page content
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. 2020 Aug 19;8(1):coaa077.
doi: 10.1093/conphys/coaa077. eCollection 2020.

Bidirectional cyclical flows increase energetic costs of station holding for a labriform swimming fish, Cymatogaster aggregata

Sarah M Luongo  1 , Andreas Ruth  2 , Connor R Gervais  3 , Keith E Korsmeyer  4 , Jacob L Johansen  5 , Paolo Domenici  6 , John F Steffensen  2
Affiliations

Bidirectional cyclical flows increase energetic costs of station holding for a labriform swimming fish, Cymatogaster aggregata

Sarah M Luongo et al. Conserv Physiol. .

Abstract

Wave-induced surge conditions are found in shallow marine ecosystems worldwide; yet, few studies have quantified how cyclical surges may affect free swimming animals. Here, we used a recently adapted respirometry technique to compare the energetic costs of a temperate fish species (Cymatogaster aggregata) swimming against a steady flow versus cyclical unidirectional and bidirectional surges in which unsteady swimming (such as accelerating, decelerating and turning) occurs. Using oxygen uptake (ṀO2) as an estimate of energetic costs, our results reveal that fish swimming in an unsteady (i.e. cyclical) unidirectional flow showed no clear increase in costs when compared to a steady flow of the same average speed, suggesting that costs and savings from cyclical acceleration and coasting are near equal. Conversely, swimming in a bidirectional cyclical flow incurred significantly higher energetic costs relative to a steady, constant flow, likely due to the added cost of turning around to face the changing flow direction. On average, we observed a 50% increase in ṀO2 of fish station holding within the bidirectional flow (227.8 mg O2 kg-1 h-1) compared to a steady, constant flow (136.1 mg O2 kg-1 h-1) of the same mean velocity. Given wave-driven surge zones are prime fish habitats in the wild, we suggest the additional costs fish incur by station holding in a bidirectional cyclical flow must be offset by favourable conditions for foraging and reproduction. With current and future increases in abiotic stressors associated with climate change, we highlight the importance of incorporating additional costs associated with swimming in cyclical water flow in the construction of energy budgets for species living in dynamic, coastal habitats.

Keywords: Cyclical flow; oxygen uptake; respirometry; station holding; swim tunnel.

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Figures

Figure 1
Figure 1
Unidirectional (solid black line) and bidirectional (solid red line) flow and predicted oxygen uptake rates (ṀO2,P2) (wave period = 5 s). The unidirectional flow is described as y = |0.73sin(2π0.2 t)| + 1.41 and the bidirectional flow is described as y = 2.18sin(2π0.2 t). Predicted oxygen uptake rates are presented over the cyclical changes in velocity for both uni- (ṀO2,P2-UNI; dashed blue line) and bidirectional (ṀO2,P2-BI; dashed gold line) flows. Predicted values were calculated by integrating the sinusoidal equation [Equation (3)] and the modified sinusoidal equation [Equation (4)] into the power function for ṀO2 and constant swimming speed [U; Equation (2)], thus producing Equations (7) and (8), respectively. Mean ṀO2,P2-UNI and mean ṀO2,P2-BI were used for comparison to the uni- and bidirectional ṀO2 measurements (Table 2)
Figure 2
Figure 2
Oxygen uptake rate (ṀO2; mg O2 kg−1 h−1) in relation to swimming speed for Cymatogaster aggregata (n = 7) in constant flow (mean ± s.d.), fit to a power function: ṀO2 = 120.27 ± 7.12 + 6.92 ± 4.70 U2.31 ± 0.59, r2 = 0.75. Black dashed lines represent individual power functions for each of the seven fish (Table 2) and black circles represent the mean ṀO2 of each fish at the corresponding speed. ṀO2,P1-UNI (blue triangle; mean ± s.d., 148.4 ± 13.2 mg O2 kg−1 h−1), and ṀO2,P1-BI (gold triangle; mean ± s.d., 136.1 ± 13.7 mg O2 kg−1 h−1) are the mean ṀO2 values at the same absolute mean swimming speed for uni- and bidirectional cyclical flow treatments, 1.87 and 1.39 BL s−1, respectively. The r-squared value for the power function was calculated by subtracting the sum of squares of the data from the sum of squares of the residuals and subtracting it from one
Figure 3
Figure 3
Oxygen uptake rate (ṀO2; mg O2 kg−1 h−1) for unidirectional and bidirectional cyclic flow treatments (n = 11) compared to the two predicted values for each treatment (n = 7). Boxes represent the first- and third quartiles; bold lines indicate median values. Whiskers denote variability outside of the quartiles and open circles represent outliers. Black circles represent individual values for each fish. ṀO2,P1 values for each flow regime are generated from the assumption that fish in a cyclical flow would have the same ṀO2 at the same absolute mean swimming speed as in a stepwise constant flow [Equations (5) to (6), respectively]. Mean ṀO2,P2 values for each flow regime are derived from integrating the modified sinusoidal wave function in the hydrodynamic power function for ṀO2 [Equation (7) to (8), respectively ]. There was no significant difference between ṀO2 of the unidirectional flow compared to either predicted value; however, there was a significant difference between ṀO2 of the bidirectional flow compared to both predicted values (P < 0.001)
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