Experimental rearing and growth of planktonic Octopus vulgaris from hatching to settlement

The common octopus, Octopus vulgaris, weighing 1.4 mg at hatching and reared in the laboratory (mean 21.2 degrees C), doubled their weight roughly every 8.5 days to a mean of 173.2 mg after 60 days when they became benthic. Changes in paralarval allometry during development were strongly marked in the case of arm length: suckers were added and the arms grew concomitantly from day 10 and growth rate accelerated from day 20. Neither cannibalism nor schooling behaviour occurred during the planktonic stage. Survival rate to settlement was 8.9%. The paralarvae of O. vulgaris exhibited presettlement reflexes from day 36 and settled between days 47 and 54, suggesting considerable potential for dispersal. Comparison of these results with previous studies suggests that paralarvae settle when they reach a critical size irrespective of age, and that the duration of the planktonic period is probably temperature dependent. After settlement, octopuses still bore Koelliker organs, lacked papillae on the body surface, were capable of feeding on inert prey, and exhibited negative phototaxis and reclusive behaviour like adults. The main period of settlement under natural conditions in the northwestern Mediterranean Sea is probably September-October.