Fisheries Research Institute, Tokushima Agriculture, Forestry and Fisheries Technology Support Center, Dounoura, Seto-cho, Naruto, Tokushima 771-0361, Japan
Daggertooth pike conger Muraenesox cinereus of 191 to 757 g in body mass caught off Tokushima Prefecture in the Kii Channel were used for these experiments. These fish were individually reared in 200 L aquaria under running water with bottom sediments of sand (1.79 mm, 1.02, 0.48 in mean grain size), muddy sand (0.162 mm), and sandy mud (0.073 mm), and the burrowing behavior in captivity and influence on burrowing behavior by the grain size of bottom sediment were examined from June 2008 and June 2009. In aquaria with sandy mud bottom sediment and muddy sand bottom sediment, Muraenesox cinereus burrowed head-first, repeatedly advancing forward and moving backward using its sharp head in the mud, but this behavior was not observed in sand bottom sediments. These laboratory experiment results show that for burrowing the sediment needs to contain mud and in the field Muraenesox cinereus is distributed in muddy sediment areas. Casts of burrows showed the following common structural features: a U-shaped tunnel of 6.8 to 15.7 cm depth with two openings; the center of the burrow was curved horizontally and the floor was flat. Many Muraenesox cinereus made burrows one after another without staying in a fixed burrow.