Rethinking swimming performance tests for bottom-dwelling fish: the case of European glass eel (Anguilla anguilla)
Paolo Vezza, F. Libardoni, Costantino Manes, Tatsuo Tsuzaki, Walter Bertoldi, Paul S. Kemp
Abstract
Abstract Systematic experiments on European eel ( Anguilla anguilla ) in their juvenile, early life stage (glass eel), were conducted to provide new insights on the fish swimming performance and propose a framework of analysis to design swimming-performance experiments for bottom-dwelling fish. In particular, we coupled experimental and computational fluid dynamics techniques to: (i) accommodate glass eel burst-and-coast swimming mode and estimate the active swimming time (t ac ), not considering coast and drift periods, (ii) estimate near-bottom velocities (U b ) experienced by the fish, rather than using bulk averages (U), (iii) investigate water temperature (T) influence on swimming ability, and (iv) identify a functional relation between U b , t ac and T. Results showed that burst-and-coast swimming mode was increasingly adopted by glass eel, especially when U was higher than 0.3 ms -1 . Using U rather than U b led to an overestimation of the fish swimming performance from 18 to 32%, on average. Under the range of temperatures analyzed (from 8 to 18 °C), t ac was strongly influenced and positively related to T. As a final result, we propose a general formula to link near-bottom velocity, water temperature and active swimming time which can be useful in ecological engineering applications and reads as $${\rm{U}}_{\rm{b}}=0.174\cdot \left({{\rm{t}}_{\rm{ac}}}^{-0.36}\cdot {\rm{T}}^{0.77}\right)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>U</mml:mi> <mml:mi>b</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.174</mml:mn> <mml:mo>·</mml:mo> <mml:mfenced> <mml:msup> <mml:mrow> <mml:msub> <mml:mi>t</mml:mi> <mml:mi>ac</mml:mi> </mml:msub> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>0.36</mml:mn> </mml:mrow> </mml:msup> <mml:mo>·</mml:mo> <mml:msup> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.77</mml:mn> </mml:mrow> </mml:msup> </mml:mfenced> </mml:mrow> </mml:math> .