Reproductive characteristics of the big blue octopus, Octopus cyanea (Gray 1849) in Zanzibar coastal waters, Tanzania

The big blue octopus, Octopus cyanea (Gray 1849) is heavily fished in Zanzibar coastal waters, yet several aspects of its biology remain unstudied in the area. The reproductive biology of O. cyanea (Gray 1849) was investigated, including sex ratios, length-weight relationships, size at maturity, and seasonal variation in maturity and spawning activity. Sampling of specimens caught by local fishers was conducted monthly at four sites. Octopus size and weight were measured and the sex determined, whereafter their gonads were extracted and staged. Female octopuses dominated the sex ratio across most size classes and seasons. Males reached sexual maturity at a smaller size than females and mature individuals of both sexes were present throughout the year, suggesting continuous spawning activity. Based on the gonadosomatic index (GSI), peak spawning periods were in June and October. The new insights into the reproductive dynamics of O. cyanea are important for fisheries management efforts and effective conservation of the species.