In the spawing season, sound production of captive walleye pollock Theragra chalcogramma (Pallas) was examined by the grunt call projection method. The pollock emitted four patterns of grunt calls, namely threatening call, aggressive-attacking call, courting call, and mating call. The sound frequency of these grunt calls is less than 800 Hz. The characteristics of walleye pollock behaviour matching each grunt call are as follows:
(1) Only one threatening grunt call was emitted by the superior male to threaten other males encountered.
(2) Aggressive-attacking grunt calls were emitted from two to five times in order to drive out other males from the male's occupied space. Behaviour included chasing, dorsal mounting and lateral mounting.
(3) Courting calls were emitted from six to twelve times in order to court other males and females which are characterized by swimming faster than usual. The behaviour included chasing, dorsal mounting and lateral mounting.
(4) Mating grunt calls were made more than thirteen times in order to mate with mature females. Behaviour included chasing, and dorsal, lateral and ventral mounting.