Effects of caudal fin size on tail-flip jump performance

Fishes are generally considered to be fully aquatic, but some voluntarily strand themselves on land to escape poor water conditions, predators, or to exploit terrestrial niches. The tail-flip jump is a method of terrestrial locomotion performed by small fishes without apparent morphological specialization, but few studies have investigated the role the caudal fin has on the tail-flip jump. We hypothesized that fish with larger caudal fins would perform shorter individual tail-flip jumps and not be able to sustain jumping in extended terrestrial excursions. Zebrafish (Danio rerio) are an excellent model to investigate this because these fish perform the tail-flip jump and some strains have been selectively bred in the pet trade industry for larger fins. In this study, wildtype and longfin zebrafish were compared because of the larger caudal fins of the longfin zebrafish. Individuals of each strain performed three consecutive jump trials with 48 h between each trial: kinematic, voluntary, and exhaustion. The kinematic trial used a high-speed camera to measure kinematic variables of individual jumps. The voluntary trial recorded each fish's voluntary response to stranding for three minutes. The exhaustion trial recorded the fish's response to be constantly elicited to jump until exhaustion was reached. Despite differences in caudal fin area, there were no differences in the kinematic characteristics of individual jump performances, including jump distance. However, wildtype zebrafish performed more jumps, jumped more than they flopped, and moved a greater total distance in both voluntary and exhaustion trials despite moving for similar durations and reaching exhaustion at similar times. These findings imply that larger fins do not affect a fish's ability to perform individual tail-flip jumps but does cause fish to employ different behavioral strategies when stranded for longer durations on land.

Terrestrial capabilities of invasive fishes and their management implications

Amphibious fishes have many adaptations that make them successful in a wide variety of conditions, including air-breathing, terrestrial locomotor capabilities, and extreme tolerance of poor water quality. However, the traits that make them highly adaptable may allow these fishes to successfully establish themselves outside of their native regions. In particular, the terrestrial capabilities of invasive amphibious fishes allow them to disperse overland, unlike fully aquatic invasive fishes, making their management more complicated. Despite numerous amphibious fish introductions around the world, ecological risk assessments and management plans often fail to adequately account for their terrestrial behaviors. In this review, I discuss the diversity of invasive amphibious fishes and what we currently know about why they emerge onto land, how they move around terrestrial environments, and how they orient while on land. In doing so, I use case studies of the performance and motivations of nonnative amphibious fishes in terrestrial environments to propose management solutions that factor in their complete natural history. Because of their terrestrial capabilities, we may need to manage amphibious fishes more like amphibians than fully aquatic fishes, but to do so, we need to learn more about how these species perform in a wide range of terrestrial environments and conditions.

Patterns and processes in amphibious fish: biomechanics and neural control of fish terrestrial locomotion

Amphibiousness in fishes spans the actinopterygian tree from the earliest to the most recently derived species. The land environment requires locomotor force production different from that in water, and a diversity of locomotor modes have evolved across the actinopterygian tree. To compare locomotor mode between species, we mapped biomechanical traits on an established amphibious fish phylogeny. Although the diversity of fish that can move over land is large, we noted several patterns, including the rarity of morphological and locomotor specialization, correlations between body shape and locomotor mode, and an overall tendency for amphibious fish to be small. We suggest two idealized empirical metrics to consider when gauging terrestrial 'success' in fishes and discuss patterns of terrestriality in fishes considering biomechanical scaling, physical consequences of shape, and tissue plasticity. Finally, we suggest four ways in which neural control could change in response to a novel environment, highlighting the importance and challenges of deciphering when these control mechanisms are used. We aim to provide an overview of the diversity of successful amphibious locomotion strategies and suggest several frameworks that can guide the study of amphibious fish and their locomotion.

Extreme Anatomy: The Lottery Winners, Specialists, and Extreme Adaptations That Are No More

This special issue of The Anatomical Record explores extravagant adaptions that vertebrates have evolved from their base groups to survive in the most challenging environments. It stems from a symposium entitled "Extreme Anatomy: Living beyond the edge," which was held April 23, 2017, at the annual meeting of the American Association for Anatomy, in Chicago, IL. In Part 1 of this issue, we examined extreme morphologies that allow exploration of new niches. In this issue, we return to the evolution of terrestriality by digging deeply into the fossil history of the piscine antecedent of tetrapods. These were truly "lottery winners" among vertebrates. This issue also bears on extreme specialists that once thrived but are now long extinct and some extant species that thrive in the hottest terrestrial niches. Herein, several contributions discuss developmental strategies that facilitate later demanding locomotor regimens and feeding strategies for accessing nutrients from less than ideal food sources. From mole-rats to short-faced breeds of domestic dogs, we encounter another host of the most unusual of earth's creatures, who have much to teach us about our world. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:214-217, 2020. © 2019 American Association for Anatomy.

Emersion and Terrestrial Locomotion of the Northern Snakehead (Channa argus) on Multiple Substrates

Most 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.

Amphibious fish 'get a jump' on terrestrial locomotor performance after exercise training on land

Many amphibious fishes rely on terrestrial locomotion to accomplish essential daily tasks, but it is unknown whether terrestrial exercise improves the locomotor performance of fishes on land. Thus, we tested the hypothesis that terrestrial exercise improves locomotion in amphibious fishes out of water as a result of skeletal muscle remodeling. We compared the jumping performance of Kryptolebias marmoratus before and after an exercise training regimen, and assessed the muscle phenotype of control and exercise-trained fish. We found that exercise-trained fish jumped 41% farther and 48% more times before reaching exhaustion. Furthermore, exercise training resulted in the hypertrophy of red muscle fibers, and an increase in red muscle capillarity and aerobic capacity. Lactate accumulation after jumping indicates that white muscle is also important in powering terrestrial jumps. Overall, skeletal muscle in K. marmoratus is highly responsive to terrestrial exercise, and muscle plasticity may assist in the effective exploitation of terrestrial habitats by amphibious fishes.