Activity Rhythm of Juvenile Walleye Pollock

Materials and methods

Using an indoor tank, we measured the behavior of pollock fry (average total length: 9 cm) using infrared sensors under the conditions shown in Table 1. LD in the table indicates light (6:00-18:00, 100 lx) and dark (18:00-06:00, 0 lx) conditions, LL indicates constant light (100 lx), and DD indicates constant dark (0 lx) conditions.

The following three figures show the number of counts (activity index) by the sensor at each time of day for three days under LD: light/dark, D: dark, and L: light conditions. In the LD condition, activity gradually slows down from 18:00 when the lights go out and becomes more active around 06:00 when the lights turn on. On the other hand, in D, the rhythmic change is rather evident on the first day, but no clear change is observed after that time. In L, no diurnal changes in activity were observed. When endogenous rhythms have a strong influence on activity, it is often the case that a specific activity cycle is maintained under homeostatic conditions, and the phase shifts gradually with respect to time (free run). However, these results do not show such a tendency.



These results suggest that light acts as a tuning factor for activity in juvenile walleye pollock and that endogenous rhythms do not play a major role in the activity cycle.

Excerpted from Yasuzumi Fujimori, Daisuke Shiode, Noriko Baba, Susumu Shimizu, and Teisuke Miura, Behavior of Juvenile Walleye Pollock Theragra chalcogramma in Relation to Time and Illuminance, Nippon Suisan Gakkaishi, 65(1), 26-32 (1999)