Feeding intensity and molecular prey identification of the common long-armed octopus, Octopus minor (Mollusca: Octopodidae) in the wild

Abstract

The common long-armed octopus, Octopus minor, is an important component of systems and supports the local fisheries in the coastal areas of northern China. And because of the overfishing, the national germplasm reserve was established as conservation area at the Moon Lake for the genetic resource of O.minor in 2012. For the fishery management and artificial breeding, especially for the management of exclusive conservation reserves, its role in the ecosystem requires assessment. Therefore, the feeding intensity of O. minor was studied from April to July 2014 when females reaching maturation, and prey composition was identified from stomach contents using a DNA barcoding method. Of the 172 sampled octopuses, 66 had stomach contents that were nearly digested into pulp. Maximum feeding intensity occurred during the month of April and the feeding intensity of the females was greater than that of the males in April and May. A considerable overall reduction of feeding intensity in both sexes occurred from April to July. A total of 8 species were identified as the prey of O. minor. Based on homology searches and phylogenetic analysis, of 60 sequences, 30 matched with fish (50.00%, by number), 13 with crustaceans (21.66%), one with annelid (1.66%), one with nematode (1.66%) and 15 with itself (25.00%). These results confirm that O. minor has habitual nature of strong dietary preference, with Gobiidae families (62.79%, by number) being an important prey during the time when females reach sexual maturation. From April to July, the observed cannibalism showed an increasing trend.