Water velocity preferences of two benthic fishes, spined loach Cobitis taenia and Northern golden loach Sabanejewia baltica: an experimental approach

Abstract

Bottom-dwelling fishes with low swimming capacity burrow into soft substrates or occupy shelters, such as stones and vegetation, to reduce metabolic costs of holding their position in running waters. As a consequence, under natural conditions it can be difficult to examine the effect of water flow as the limiting factor of benthic fishes. The velocity (0, 10, 20, and 30 cm s⁻¹) preferences of spined loach and Northern golden loach were examined experimentally in an isosceles, cross-shaped acrylic tank with five square chambers (side of 15 cm and 40 cm high). Fish could select freely between a sheltered place without water flow (two side cells) and with flow (three) cells. Fishes were observed for 40 min by taking time-lapse photos every 0.5 min, with the first 7.5 min (= 15 photos) treated as an acclimatization period. Each treatment was repeated 10 times with 65 photos analysed. The disparity between the proportion of fish observed in the active and passive areas of the tank was used as the preference or avoidance of the velocity treatment. Northern golden loach showed a random distribution between cells (no bias from a proportion of 3:2), only at a velocity 0 cm s⁻¹ revealing strong preference for water flow 10 and 20 cm s⁻¹ and avoidance of velocity of 30 cm s⁻¹. Spined loach preferred a velocity of 10 cm s⁻¹ and avoided velocities of 20 and 30 cm s⁻¹. Surprisingly fish were not randomly distributed at a velocity of 0 cm s^−1, at which they were more frequently found in passive cells than active ones. The results confirm that Northern golden loach is a rheophilic fish occurring only in running waters, whereas spined loach is an ubiquitous species distributed in slow-flowing as well as stagnant waters.

Keywords:

• Cobitids
• water velocity
• mobility
• selectivity index

Acknowledgements

Special thanks are extended to C. Smith for English correction and the useful suggestions on an earlier version of this manuscript. The study was performed with ethical permission from the Local Ethics Committee (23/ŁB463/2009) and the General Directorate of Environmental Protection (DO Pozgiz-4200/V.42/105/09/ls) as these loaches are protected in Poland.

Authors’ contributions

T.K., M.P., and D.P. conceived this study. T.K. developed the design. D.P. and M.P. performed the experiments with input from T.K., L.M., and D.P. collected fish in the field. M.P. analysed the data and drafted the manuscript. All authors provided revisions of the final version of the manuscript.

Additional information

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the the Polish Ministry for Science and Higher Education [N N304 365 338].