First observations of the burrows of Anguilla japonica

The burrow morphology of the Japanese eel Anguilla japonica was studied using in situ resincasting in a mud bottomed tidal drainage channel adjacent to the Fukui River in Tokushima, Japan. Two eels (62.5 and 56.3 cm total length) were initially fished from the burrows to verify that they were being used by A. japonica. Casts were made of 10 burrows that were found to have from one to three openings and main tunnels that were parallel to the axis of water flow in the channel. The maximum depths of the tunnels in the mud were 17.8-30.0 cm. The diameters of main tunnels ranged from 1.2 to 7.9 cm, were almost always wider than the bodies of the Japanese eels examined, and were more variable in the horizontal axis than in the vertical axis. There were no other animals capable of constructing a long and thin burrow in this channel, so these observations indicate that anguillids are able to construct their own burrows in soft mud sediments that may be used for extended periods or time. (c) 2005 The Fisheries Society of the British Isles.