The Effect of Prey Size and Prey Density on Paralarval Feeding Success of the Common Sydney Octopus, Octopus tetricus

Global demand for octopus seafood has been increasing over the past 30 years. This demand is projected to increase further as coastal communities and seafood consumers seek alternative sources of protein as finfish stocks decline. The establishment of a sustainable octopus aquaculture would have the potential to alleviate fishing pressures from wild populations. Commercial-scale octopus aquaculture, however, has not been achieved due to the difficulty of successfully rearing octopus paralarvae on an efficacious diet. This study investigated the prey size and density preferences of Octopus tetricus paralarvae to understand the characteristics that improve food acquisition during rearing. Groups of octopus paralarvae from multiple broods were observed for a range of feeding behaviour including positioning, attack, capture loss, successful capture and handling time when given different treatments of Artemia prey. Prey size experiments used treatments of Artemia with total lengths of < 0.5, 0.9–1.0 and 1.4–1.6 mm, while prey density experiments used 0.2, 0.6, 1.0, 1.4, 1.8 and 2.2 Artemia mL⁻¹. Increased numbers of successful feeding behaviours (e.g., positionings, attacks and successful captures) were directly observed with increasing prey size. Octopus paralarvae performed 52% more positionings, 100% more attacks and 175% more successful captures when given large Artemia (1.4–1.6 mm) than when given small Artemia (< 0.5 mm). Likewise, the number of observed successful feeding behaviours tended to increase with increasing Artemia density but sharply decreased at the highest density treatment (2.2 Artemia mL⁻¹). Paralarvae performed up to 109% more positionings, 307% more attacks and 300% more successful captures when given prey densities of 1.0–1.8 Artemia mL⁻¹ than when given lower prey density treatments and 2.2 Artemia mL⁻¹. The results from this study indicate that prey size and density are crucial for the successful feeding of octopus paralarvae. Based on the greatest numbers of successful feeding behaviours, O. tetricus paralarvae prefer prey between 1.4 and 1.6 mm in length and at densities between 1.0 and 1.8 prey mL⁻¹. The use of these optimal prey characteristics can be used to promote efficient paralarval octopus prey capture and feeding to greatly increase food intake in octopus paralarvae when reared in aquaculture.