Abstract
To determine the role of geotaxis in the control of the distribution and the vertical migration of sole larvae and juveniles during development, sets of experiments using visual observations with an IR converter in total darkness were carried out in transparent vertical tank, horizontal white light beam coming through the tank. Observations clearly demonstrate geotactic reactions and geotaxis changes during development. Under artificial light intensities of diurnal values, between 1000 and 10 μw. cm‐1, the very young larvae (stage I) exhibit geopositive reactions; then, from about four days post hatching to metamorphosis, the number of geonegative reactions increases progressively. At and after metamorphosis, sole only exhibit geonegative reactions at artificial irradiances corresponding to nocturnal values (below 1 μw. cm‐2). The possible effects of geotaxis in each developmental stage, are discussed with respect of photokinesis changes during ontogenesis.
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