Fish responses to flow velocity and turbulence in relation to size, sex and parasite load

Abstract

Riverine fish are subjected to heterogeneous flow velocities and turbulence and may use this to their advantage by selecting regions that balance energy expenditure for station holding while maximizing energy gain through feeding opportunities. This study investigated microhabitat selection by guppies Poecilia reticulata in terms of flow characteristics generated by hemisphere boulders in an open channel flume. Velocity and turbulence influenced the variation in swimming behaviour with respect to size, sex and parasite intensity. With increasing body length, fish swam further and more frequently between boulder regions. Larger guppies spent more time in the areas of high-velocity and low-turbulence regions beside the boulders, whereas smaller guppies frequented the low-velocity and high-turbulence regions directly behind the boulders. Male guppies selected the regions of low velocity, indicating possible reduced swimming ability owing to hydrodynamic drag imposed by their fins. With increasing Gyrodactylus turnbulli burden, fish spent more time in regions with moderate velocity and lowest turbulent kinetic energy which were the most spatially and temporally homogeneous in terms of velocity and turbulence. These findings highlight the importance of heterogeneous flow conditions in river channel design owing to the behavioural variability within a species in response to velocity and turbulence.

Are fancy guppies (<em>Poeciliareticulata</em> Peters, 1859) invasive?

“…Karino et al (2006), in addition to showing that the guppies with longer tails exhibiting poorer swimming performances, have also shown that these long-tailed guppies are restricted into low water flow velocity microhabitats in streams. The investigation of Hockley et al (2014) also support the above findings of Karino et al (2006). All these findings suggest an interesting ecological phenomenon of 'habitat partitioning' (Hutchinson 1959) among the wild, yellow and black guppies if they were allowed to co-occur in streams.…”

“…For example, the yellow guppies had higher standard length than that of the black guppies. Hockley et al (2014) showed that guppies with increased standard length were more active and spent more time in areas of both high velocity and low velocity water flow. Although longer fins serve as secondary sex characteristics in guppies, the larger fins increased the hydrodynamic drag compared to smaller fins.…”

“…Kolluru et al (2006Kolluru et al ( , 2007 also showed that the fin regeneration in guppies is possible even in the presence of natural stressors such as predators and infectious agents, and they regrew more fin tissues when the food level was raised. Hockley et al (2014) have shown that the swimming speed of guppies is affected by the hydrodynamic drag imposed by their fins. Therefore, swimming speed is an important parameter to assess the fitness of the fish where the critical swimming speed helps to find out the maximum velocity that a fish can tolerate.…”

Efficiency Index Diagram for Wake Region Evaluation of Artificial Reefs Facilitated for Marine Forest Creation

“…Wake region of an AR is formed by the interaction of the reef with prevailing currents or water flows (Wolanski and Hammer, 1988). Wake regions have a high probability of recruiting seaweed spores or attracting marine species because they facilitate energy saving zones for marine species (Liao et al, 2003;Beal et al, 2006;Hockley et al, 2013) and deposition of sediments, nutrients, and bio-deposits (Sawaragi, 1995;Miller et al, 2002;Falcão et al, 2007;Prairie et al, 2012). In general, the wake region of an AR is defined as the space consisting of the recirculating water flow immediately behind the AR (Sheng, 2000;Oh et al, 2011).…”

“…Second, a certain reef function should be established to increase living marine resources and biomass, otherwise the initial goal cannot be partially or even completely achieved. This function is categorized into several elements such as gathering or attracting marine species, providing a rest, spawning, and energysaving region (Hockley et al, 2013), protecting the species from predators, and finally increasing biomass and diversity. Quantification of these elements in terms of physical measures has been carried out (Kim et al, 2016b), for example efficiency, tranquility, and stability indices of an AR wake region.…”