Ontogeny of phototactic behavior in phyllosoma larvae of the Japanese spiny lobster Panulirus japonicus

The larval sinking phenomenon is a cause of mortality due to injuries to body parts and the occurrence of bacterial disease among swarming larvae at the bottom of a rearing tank during larval culture of the Japanese spiny lobster Panulirus japonicus. As a basis for developing control measures for larval behavior in tanks to improve survival, we investigated phototactic traits of stage I-X phyllosoma larvae under different light intensities (6 levels, 0.0031 μmol m−2 s−1 to 310 μmol m−2 s−1 in 10% increments) and wavelengths (14 levels, 400-660 nm in 20-nm increments) under laboratory conditions. The controls were tested in the dark. Phototactic behavior of phyllosoma larvae changed with growth and differed under the different light intensities and wavelengths. Overall, positive and negative phototaxis were recorded at high light intensities (31 and 310 μmol m−2 s−1) and at low light intensities (0.0031 and 0.031 μmol m−2 s−1), respectively. Early larvae showed positive phototactic behavior over a broad spectrum of 400-620 nm, and in larvae after the middle stage, positive phototaxis was observed at