ALBERT

Description: The larvae of the Japanese commercial octopod, Octopus (Octopus) vulgare CUVIER, were successfully reared from the swimming larvae just after hatching to the benthic young octopus in 33 to 40 days on a diet of the zoea larvae of the shrimp, Palaemon serrifer. The rearing experiments were carried out at the Hyogo Prefectural Fisheries Experimantal Station from June to September, 1962. At a start of experiments 200 individuals of the octopus larvae were kept in a glass vessel containing about 8 litre of sea-water. During the early 20 days period the sea-water of each vessel was aerated and renewed every 3rd or 4th day, and after this period the method was changed for the use of running water. The results obtained are summarized as follows: 1) From just after hatching, the larvae of the octopus were fed on the larvae of Paleamon of 2 to 4mm body-length. (See table 1) After transforming into benthic stage, they were given a small piece of ovaries, tests and hepatic glands of the crab, Charybdis japoniea. Three or four days after transforming, they were fed on small shripms and young crabs, Gaetice depressus (DE HAAN) of 5 to 7mm carapace-width. It was observed that the young octopus of 30mm total-length ate 4 or 5 young crabs in a day. 2) The survival rate of the octopus larvae was found as low as 9 percent through the free-swimming stage. However, it would be conceivably possible to raise this survival rate much higher if sufficient food supply is secured during the rearing experiments. 3) The growth of the octopus larvae in 90 days after hatching at water temperature 24.7°C (23.0~26.7°C) can be seen in Table 4 and Fig. 1. It was found that the larvae settled on the bottom 33 to 40 days after hatching, when they attained a size ranging 10~15mm in total-length (3.8~5.7mm in body-length). Once the swimming larvae transformed into the benthic young octopus, they bcame nocternal and fed on foods mainly at night. A considerable mortality occured among the young octopus, which was caused by cannibalism and creeping out of the rearing water. 4) The numbers of suckers found on each arm were 3 at the hatching, 5 (4~6) at 10 days, 9 (6~12) at 20 days, 19 (16~22) at 30 days, 24 (21~27) at 40 days and 22~23 when a majority of octopus larvae grew to the benthic stage.

Description: Les Cephalopodes qui font l'objet de cette petite note furent recueillis au cours de la Campagne de la Calypso dans le golfe de Guinee, pendant les mois de mai a juillet 1956. Les recoltes proviennent de dragages, de chalutages et de peches planctoniques au large du continent africain, du Senegal au Gabon, et de dragages, de plongees et de peches a pied autour des iles S. Tome, Principe et Annobon. Le but principal de la campagne etait l'etude de la faune littorale des iles, et les conditions de travail dans cette region expliquent que les Cephalopodes captures soient peu nombreux. Je me fais un devoir de remercier M. le Professeur L. FAGE et M. J. FoREST d'avoir bien voulu me confier l'etude de ce materiel.