マダコの平衡石の相対成長ならびに成長過程

抄録

The relative growth and development processes of the statoliths in Octopus vulgaris were investigated from specimens collected by small beam-trawls and octopus-pots in the northeastern area of the Iyo-Nada of the Seto Inland Sea, Japan, from May, 1995 to June, 1996. Eggs, their mothers were identified as O. vulgaris, were cultured at the Ehime Prefectural Chuyo Fisheries Experimental Station in 1000/ tanks under flowing natural sea water conditions and the hatchlings were collected to obtain their statoliths. The shape of the statolith in adults was like an oblique circular cone and the nucleus was shaped as a dome on the top of the statolith. The statolith of hatchlings was egg-shaped. To calculate the relative growth, 1101 pairs of statoliths and the ventral mantle length from adults were used. The relationship between the statolith length and the ventral mantle length showed a break point at 80.0mm in the ventral mantle length in males and at 70.3mm in females. It is possible that the statoliths of the paralarvae grew concentrically during the planktonic phase because the nuclei in the statoliths of adults, nuclei which are statoliths in paralarvae, were larger than the statoliths in hatchlings (Mann-Whitney test, Ps<0.001), and the statoliths changed the direction of growth in the vicinity of settlement. A growth model of the statolith was drawn with allometric equations between the length and height, and the length and width in the statoliths.