How american eels Anguilla rostrata construct and respire in burrows

Abstract

We investigated the burrowing behaviour of growth-phase (yellow) American eel Anguilla rostrata, a nocturnal fish that occupies the substrate during daylight hours and during winter. Eels formed burrows by forcing the head, then the body, into the substrate with rapid body undulations. Eels excavated from mud showed highly variable postures. In 10 of 15 experiments, the eel’s mouth was at or slightly above the surface. In the remaining experiments, the eel’s mouth was a mean of 3.5 cm below the surface, and an inhalation shaft ran from the surface to the mouth. Eels probably advance through mud by alternately pushing and anchoring the anterior and posterior parts of the body. Eel burrows observed in the lab and the field had up to 5 openings. Craters or mounds formed around some winter burrow openings due to head or tail movements or sediment erosion. Flat openings and openings in which the eel plugged the burrow entrance were found in both summer and winter. Dye trace experiments indicated that eels in mud and pebble burrows draw water from the water column into the mouth and exhale it through the gill openings. Because eels in burrows use water from the water column for respiration, the spread of anthro-pogenically induced anoxia and hypoxia in coastal waters poses an increasing conservation threat.