Net cage and cement tank culture of common Atlantic octopus Octopus vulgaris in Nanji Island, Zhejiang Province

From 2005 Nov. to 2006 Jan., a preliminary experiment on Octopus vulgaris culture was carried out. Totally 22 062 wild octopus larvae were cultured in 55 net cages and 18 cement tanks respectively. In the experiment, the initial average weight of 10 912 octopus cultured in net cages was only 233.6 g. After 40 days, the average weight increased to 660.9 g, with a survival rate of 62.8%. The daily weight gain rate was 2.389% and food conversion ratio was 8.08. The original average weight of 11 150 octopus cultured in cement tanks was 220.5 g. In the first stage of experiment, the average weight reached 364.5 g after 33 days, with a survival rate of 70.9%. The daily weight gain rate was 1.402% and food conversion ratio was 6.04. The second stage was carried out in winter. In the 53-day experiment, the average weight reached 489.5 g, with high mortality and low daily weight gain rate of 44.3% and 0.552%, respectively. The food conversion ratio was 8.97. The economical benefits of net cage culture was higher than that of cement tank culture, with the ratio of input to output of 1：1.210, while that of the latter was 1：1.105. In this paper, factors that may affect the growth and survival of O.vulgaris, the murdering and autotomy behaviors were also discussed.