Amphibious adaptations in a newly recognized amphibious fish: Terrestrial locomotion and the influences of body size and temperature KIT MAGELLAN* Department of Ichthyology and Fisheries Sciences, Rhodes University, Grahamstown, South Africa (Email: kit8x@hotmail.com; kitmagellan@gmail.com) Abstract Amphibious animals are adapted for both aquatic and terrestrial habitats. The conflicting requirements for dual habitats are perhaps most pronounced in the air-breathing fishes, which represent an intermediate stage between the totally aquatic habitat and terrestrial colonization. A key requirement for amphibious fishes is terrestrial locomotion. The different densities and compositions of air and water impose constraints for efficient terrestrial locomotion that differ from those required for aquatic locomotion. I investigated terrestrial locomotion in a small South African fish, Galaxias ‘nebula’, by exposing 60 individual fish to air in specially designed raceways and quantifying movement type and occurrence as a function of availability of water, fish size and environmental temperature. Nebula showed a sustained undulating form of terrestrial locomotion characteristic of amphibious fishes and also a transient ballistic locomotion (jumps) typical of fully aquatic species. Terrestrial movement was influenced by fish size, with medium- sized fish undertaking more jumps towards water, and fewer jumps away from water, than their smaller or larger conspecifics. In contrast, axial undulation was mainly influenced by temperature. However, there was no consistent pattern in temperature effects presumably because temperature is just one of a suit of environmental factors that may affect terrestrial locomotion. Nebula’s amphibious adaptations allow it to cope with the unpredictability inherent in its natural environment. Key words: air-breathing fish, amphibious adaptations, body size, environmental factors, Galaxias ‘nebula’, temperature, terrestrial locomotion. INTRODUCTION Amphibious animals are adapted for both aquatic and terrestrial habitats and divide their lives periodically (e.g. Yeomans 1995; Dall’Antonia & Sinsch 2001) or ontogenetically (e.g. Martin et al. 2004; Blob et al. 2007) between water and land (Sayer & Davenport 1991; Sayer 2005). The use of terrestrial environments imposes a range of environmental and physiological conditions that are not encountered in water, and am- phibious species undergo selection for a variety of mor- phological, physiological and behavioural adaptations to accommodate these requirements (Sayer & Davenport 1991; Sayer 2005; Gibb et al. 2013). However, in all cases, water is crucial for survival (Sayer & Davenport 1991; Sayer 2005; Pace & Gibb 2014); major require- ments for all amphibious species are avoidance of dehydration and maintenance of thermal balance (Yeomans 1995; Dall’Antonia & Sinsch 2001; Sayer 2005). Terrestrial environments are thus inherently risky for animals that rely on water, and multiple adap- tations are likely to be required for successful navigation around terrestrial environments. The conflicting requirements for aquatic and terres- trial life are perhaps most pronounced in air-breathing fishes (Sayer & Davenport 1991; Graham 1997; Sayer 2005). Not all air-breathing fishes are amphibious. Aquatic air breathers periodically break the water surface to gulp air but never leave water (Gonzales et al. 2006). Amphibious fishes, on the other hand, are those that spend periods of time out of water as a normal part of their life history (Sayer & Davenport 1991; Graham 1997; Sayer 2005). These fishes utilize atmospheric oxy- gen during periods of air exposure and may be capable of surviving considerable periods without surface water (Graham 1997; Sayer 2005; Taylor et al. 2008). In gen- eral, more amphibious fishes spend a greater proportion of their time out of water and are better adapted for the terrestrial environment; fish that only briefly leave water tend to retain mainly aquatic attributes, while others that are well adapted for prolonged periods of aerial exposure may be considered as semi-terrestrial (Graham et al. 1985; Yoshiyama et al. 1995; Sayer 2005). Like other amphibious species, fishes may leave water to avoid predation, competition, or unfavourable aquatic condi- tions, or for terrestrial activities such as feeding or reproduction (reviewed in Sayer & Davenport 1991). However, amphibious fishes are commonly closely asso- ciated with water and in many cases are better adapted for aquatic living (Sayer & Davenport 1991; Sayer 2005; *Corresponding author. Accepted for publication September 2015. Austral Ecology (2016) ••, ••–•• © 2016 Ecological Society of Australia doi:10.1111/aec.12332