Abstract
SynopsisMost fishes known for terrestrial locomotion are small and/or elongate. Northern snakeheads (Channa argus) are large, air-breathing piscivores anecdotally known for terrestrial behaviors. Our goals were to determine their environmental motivations for emersion, describe their terrestrial kinematics for fish 3.0–70.0 cm and compare kinematics among four substrates. For emersion experiments, C. argus was individually placed into aquatic containers with ramps extending through the surface of the water, and exposed to 15 ecologically-relevant environmental conditions. For kinematic experiments, fish were filmed moving on moist bench liner, grass, artificial turf, and a flat or tilted rubber boat deck. Videos were digitized for analysis in MATLAB and electromyography was used to measure muscular activity. Only the low pH (4.8), high salinity (30 ppt), and high dCO2 (10% seltzer solution) treatments elicited emersion responses. While extreme, these conditions do occur in some of their native Asian swamps. Northern snakeheads >4.5 cm used a unique form of axial-appendage-based terrestrial locomotion involving cyclic oscillations of the axial body, paired with near-simultaneous movements of both pectoral fins. Individuals ≤3.5 cm used tail-flip jumps to travel on land. Northern snakeheads also moved more quickly on complex, three-dimensional substrates (e.g., grass) than on smooth substrates (e.g., bench liner), and when moving downslope. Release of snakeheads onto land by humans or accidentally by predators may be more common than voluntary emersion, but because northern snakeheads can respire air, it may be necessary to factor in the ability to spread overland into the management of this invasive species.
Highlights
IntroductionA diversity of fishes exhibit a variety of terrestrial behaviors for a range of reasons, such as to escape onto land away from aquatic predators (Walker 1952; Goodyear 1970; Abel et al 1987; Martin et al 2004; Swanson and Gibb 2004; Blob et al 2010; Hsieh 2010; Kawano and Blob 2013; Magellan 2015), to feed on land and access new resources (Mast 1915; Das 1928; Graham 1970; Wright and Raymond 1978; Graham et al 1985; Gordon et al 1985a; Van Wassenbergh et al 2006; Taylor et al 2008; Pronko et al 2013; Van Wassenbergh 2013; Bressman et al 2016, 2018a, 2018b), or to alleviate competition for resources (Huehner et al 1985; Liem 1987)
Welch’s two sample t-tests were used to compare kinematic parameters between forward and backward crawling behaviors, as well as between individuals on turf with and without electrodes implanted. In both the control and hypoxia treatments, northern snakeheads showed no signs of distress, which could have included erratic swimming, inability to remain horizontal in the water column, and rapid ventilation
No northern snakeheads emerged from the water during the control or hypoxia treatments (Table 1), but individuals did emerge when exposed to acidic conditions, high salinity, and high levels of dCO2 (Supplementary Fig. S2)
Summary
A diversity of fishes exhibit a variety of terrestrial behaviors for a range of reasons, such as to escape onto land away from aquatic predators (Walker 1952; Goodyear 1970; Abel et al 1987; Martin et al 2004; Swanson and Gibb 2004; Blob et al 2010; Hsieh 2010; Kawano and Blob 2013; Magellan 2015), to feed on land and access new resources (Mast 1915; Das 1928; Graham 1970; Wright and Raymond 1978; Graham et al 1985; Gordon et al 1985a; Van Wassenbergh et al 2006; Taylor et al 2008; Pronko et al 2013; Van Wassenbergh 2013; Bressman et al 2016, 2018a, 2018b), or to alleviate competition for resources (Huehner et al 1985; Liem 1987). Conditions that cause amphibious fishes to emerge can be species-specific (Ebeling et al 1970; Davenport and Woolmington 1981; Abel et al 1987; Liem 1987; Sayer and Davenport 1991; Wright and Turko 2016). By developing a better understanding of factors that influence emersion, we may be able to improve management of invasive amphibious species, allowing us to predict when terrestrial behaviors and dispersion are most likely for each species
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