Automatic recording systems for lobster movements in an experimental tank
Abstract:The nighttime activity of a Japanese spiny lobster, Panulirus japonicus, is considerably suppressed when the underwater brightness is higher than a threshold value of about 1.8 × 10−4 lux. This light level is below the visual threshold for the human eye, so that special automatic devices are required. We designed two types of recording systems and used them to determine diurnal movements of lobsters held in tanks in the laboratory. For the simpler of the two devices, we used a rectangular cage of 40 cm length, 30 cm width and 30 cm depth. The tension was measured in one of three wires, the lower end of which was connected to the center of the shorter edge of the cages. We defined a measure of the lobster activity as the number of occurrences of strain change larger than a prescribed strain value per unit time. The value of 2 g was usually selected for our experiments. This measure was proved to be useful for describing gross variations in the diurnal pattern of lobster movements. In the two-dimensional device, we used a cylindrical cage of 80 cm diameter, and 40 cm depth. The upper part of the cage was supported by a triangular frame made of angle aluminum. A supporting bar with a pointed tip was inclined downward from each corner of the triangular frame and placed on an electronic balance. The weight measured by the balance was automatically fed to a computer, the position in the two dimensional plane calculated, and the results recorded and stored on a computer disk. The accuracy of the position determination was < 0.9 cm. This recording system appears good enough to detect the details of the movement of the lobster in a two dimensional plane.
Document Type: Research Article
Publication date: 1997-07-01
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