Terrestrial friction-reducing properties of mucus and scale anisotropy in the amphibious Northern Snakehead (Channa argus).

Abstract

The mucus coating around a fish's body is essential to its survival. It contains antimicrobial properties, aids in drag reduction, and protects against physical damage. It is versatile in the aquatic environment but little is known about the role of mucus in amphibious fishes. The Northern Snakehead (Channa argus) is a species of amphibious fish that is not only invasive to the Chesapeake Bay but is renowned for its ability to crawl on land. However, the role of their slippery mucus in terrestrial behaviors is currently unknown. This project aims to investigate how snakehead mucus affects friction during terrestrial locomotion, assess if snakehead mucus is adapted to facilitate terrestrial movements compared to the mucus of fully-aquatic fish (i.e., Common Carp, Cyprinus carpio), and determine how snakehead scales influence frictional anisotropy compared to scale-less fish (i.e., Blue Catfish, Ictalurus furcatus). This was tested by towing freshly euthanized fish along two different substrates in the forward and backward directions using a force meter to determine the force needed to overcome static friction. The same fish was tested with its mucus coat intact and again with it wiped off to allow for paired comparisons. Snakehead mucus significantly reduced terrestrial friction, and did so significantly more than carp mucus. Additionally, fish with scales exhibited frictional anisotropy, with less friction in the forward direction and more in the backward direction, similar to how snake scale anisotropy promotes forward movement. Amphibious fishes like snakeheads may have evolved particularly slippery mucus to aid in terrestrial locomotion by reducing friction and energy required to move overland, potentially facilitating overland movement between bodies of water. This study may also provide insight to the development of artificial fish mucus for amphibious robots and other applications.