水槽内におけるイセエビの動きの追跡観測

抄録

The nighttime activity of a Japanese spiny lobster is considerably suppressed when the brightness is higher than a threshold value of about 1.8 × 10^-4 lx. This brightness value is low enough that nothing is visible by human eyes, and we need special automatic devices to trace lobster movements and to investigate lobster behaviors in dark nighttime. We designed two types of recording systems which are appreciable for our experimental tanks. Lobster cages in our experimental tank are hung by three wires or supported by three pointed vertical bars.
In a simpler devices, we used a rectangular cage of 0.4 m length, of 0.3 m width and of 0.3 m depth. The tension of one of three wires, the lower end of which is connected to the center of one shorter rim, is measured. The strain averaged for 9 sec are recorded every 15 sec. We define a measure of the lobster activity by counting the number of occurrence of strain change larger than 2 gw between successive data pair per unit time. The value of 2 gw is selected empirically for convenience sake, and corresponds to a movement of the 250 gw lobster over 3.2 cm distance in the longitudinal direction. This measure appears to be useful to describe gross natures of the diurnal variation pattern of lobster activities.
In the other devices, we use a cylindrical cage of 0.8 m diameter, and of 0.4 m depth. The upper part of the cage is supported by a triangle frame made of aluminum angles. A pointed supporting bar is set downward from each corner of the triangle frame, and is placed on an electronic balance. The weight measured by each balance is automatically fed to a personal computer, and the position in two dimensional plane is calculated and the results are recorded and kept in a floppy disk. The position of the lobster is determined in the interval of 2.7 sec, and the accuracy of the position determination is less than 0.9 cm. This recording system appears good enough to detect the detailed movement of the lobster in two dimensional plane.
The usefulness of these recording systems will be introduced with several typical experimental results.