Molecular Identification of a Frequently Landed Octopus in Fijian Artisanal Fisheries

The day octopus Octopus cyanea Gray, 1849, is a large, muscular and robust octopod distributed across the tropical Indo-West Pacific. In Fiji and other Pacific Island Countries and Territories (PICT), it is an economically, ecologically, and socio-culturally important species, and supports a small, but high-value artisanal fishery providing a basis for coastal community livelihoods. Despite its importance, the presence of this species has not been confirmed in Fiji using molecular methods. To provide taxonomic verification and inform genomic stock assessment of the Fijian octopus resource, two mitochondrial barcoding genes (cox1 and 16s rRNA, n = 60), together with morphological assessments, were applied to specimens collected from six provinces in Fiji. In both reconstructions, all Fijian sequences resolved within broader clades comprising additional O. cyanea sequences sampled across the species distribution (cox1 688bp: n = 53; 16s rRNA 572bp: n = 10), with high node support (100%) and sequence identity matches (97%–100%), confirming their conspecifity. Morphological features of Fijian specimens (n = 79) confirmed to ranges reported for O. cyanea, including mantle length, head width, sucker counts on hectocotylized arm and ligula lengths (3.47–5.94 mm). With the resolution of species identity, species-appropriate stock assessment may now proceed, to inform sustainable and accurate fishery exploitation, catch reporting and management. The independent molecular barcoding and morphological characterization approaches used have high utility for octopus fishery characterization efforts in other PICT, which remain data deficient.