Fish can swim much better than we thought

Posted on March 10, 2014

A fish’s swimming performance has a strong influence on its ability to forage, to escape from predators, and to move through high-velocity habitats. Many researchers have measured the swimming abilities of different species to compare their physiological capacities and to design effective fishways. However, recent results suggest that previous studies have dramatically underestimated fish swimming performance because they’ve typically been carried out in enclosed swim chambers or respirometers. In the new experiments, 11-19 cm-long brook trout and brown trout were placed in a low-velocity staging area from where they could move upstream at will into a long (20 m) open-channel flume. Trials were carried out at flow velocities of 1.6 and 2.5 m/s. Electronic (PIT) tags implanted into the test fish allowed the collection of data on distance of ascent, swimming speed and time to fatigue in the flume. Both species swam at speeds of 10-30 body lengths / sec: much higher rates than those recorded in previous trout studies (<10 body lengths / sec). The faster swimming speeds recorded in this study might be explained by a combination of several factors, including the possibility that the use of an unrestricted swim chamber allowed fish to take advantage of different muscle groups and the complex hydraulics of open-channel flow. For both trout species, over 80% of the variation in flume ascent distance could be explained by an equation based on flow velocity and free-choice swimming speed. The authors emphasise that fish motivation, physiological capacity and behavioural performance must all be considered when trying to understand swimming performance.

Reference: Castro-Santos, T., Sanz-Ronda, F.J. & Ruiz-Legazpi, J. 2013. Breaking the speed limit — comparative sprinting performance of brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta). Canadian Journal of Fisheries and Aquatic Sciences 70, 280–293.