The role of substrate holding in achieving critical swimming speeds: a case study using the invasive round goby (Neogobius melanostomus)

Abstract

The swimming performance of fishes has generally been assessed using a stepped velocity test where the speed at fatigue is considered the critical swimming performance (Ucrit). Although this test was designed for fishes that swim in the water column, it has been applied to fishes that adhere to the substrate. Here we examined the extent to which substrate holding, slipping and swimming contributed to reaching Ucrit in an example substrate holding fish, the invasive round goby. A linear model indicated that each behavior contributed significantly to Ucrit, but that substrate holding was by far the biggest contributor (65.8 ± 3.9 % vs. 5.8 ± 0.9 and 28.4 ± 3.4 % slipping and swimming). We also used our behavioural analysis to determine the critical substrate holding speed (Uhold: 28.6 ± 1.1 cm s−1). We conclude that the Ucrit test can be applied to substrate holding fish but that it is not just an indication of critical swimming speed as is often considered and must be interpreted with caution.