Circadian locomotor activity in Japanese sea catfish Plotosus lineatus

Abstract

To find out whether or not the locomotor activity of the Japanese sea catfish, Plotosus lineatus, shows a circadian rhythmicity, the locomotor activity of this catfish was recorded in a laboratory. All of the catfish recorded (n = 20) showed a nocturnal locomotor activity rhythm under a light-dark (LD) cycle (LD 12:12). The locomotor activity started after the light was turned off, and declined during the period of darkness. In five of the six catfish we examined, locomotor activity shifted gradually over the course of 3-4 days in order to synchronize to the LD cycle after it was advanced by 6 h. Locomotor activity persisted within a constant darkness (DD) in all eight of the catfish. The average free-running period of locomotor activity under DD lasted for 24.2 ± 0.4 h (mean ± SD). Thus, the present results demonstrate that the Japanese sea catfish has an endogenous circadian oscillator entrained by an LD cycle.

Feeding activity rhythm in Japanese sea catfish Plotosus japonicus

“…Feeding activity, measured as the number of entries into a feed box, was significantly correlated with the number of food pellets consumed, thereby demonstrating that feeding activity measured in the present experiment accurately reflects feeding behavior rather than locomotor activity. Previously, locomotor activity in P. japonicus was not observed during light periods under LD and LL conditions [6]; here, however, feeding activity was observed during the light periods under RF, and LD and LL conditions (Figs. 4b, 5a).…”

“…In contrast, a close correlation between food intake and movement patterns has been reported in Atlantic salmon, Salmo salar [14], and brown trout, Salmo trutta [15]. The Japanese sea catfish has been reported to have a nocturnal locomotor activity rhythm that is entrained by an LD cycle, and their activity typically begins at the onset of darkness and ends before the onset of light [6]. Their peak locomotor activity levels occur immediately after the onset of darkness and declines during the remaining period of darkness.…”

“…During experiments, each fish was held in a separate observation aquarium (30 9 90 9 60 cm), which served as activity recording chambers ( Fig. 1), modified from our previous paper [6] by the addition of a plastic box (7 9 11 9 10 cm) which was used to contain feed. The top of the feed box was open and allowed the fish unrestricted access the food.…”

“…The Japanese sea catfish Plotosus japonicus [5] has an endogenous locomotor activity rhythm that is entrained by light [6]; however, there are multiple behavioral components within that general locomotor activity rhythm, such as feeding, reproduction, and territoriality, which may be connected to different oscillator systems and which may be entrained by different synchronizers. In fish, as well as in mammals, the circadian system may contain two independent oscillators, one entrained by a FEO and the other by a light-entrainable oscillator (LEO) [7][8][9][10].…”

“…Adult catfish prefer to forage in groups by day for rest and scatter by night for searching foods [12]. Solitary P. japonicus is reported to show a nocturnal locomotor activity rhythm under laboratory conditions, the free-running period of locomotor activity in each fish being contained within a narrow range [6]. Such a locomotor rhythm may reflect their natural behavior in the wild and may be related to group formation.…”