Octopuses have been intensively researched for more than 50 years because of their excellent potential for aquaculture due to their high demand for human consumption. Different octopus species produce either large embryos that hatch directly into benthic juveniles or small embryos that hatch into a planktonic stage called paralarvae before transitioning through a settlement phase and becoming fully benthic. High mortalities are commonly experienced in cultured paralarvae due to the absence of suitable diets. The few successful attempts at rearing paralarvae have used zoeae larvae of various crab species as the sole or as a complimentary diet, however, zoeae cultures are labour intensive and costly. Initial feeding behaviour studies with Octopus tetricus paralarvae suggest that they rapidly accept artificial pellets, with the proportion of paralarvae capturing artificial pellets being equal to those capturing live prey.Despite the apparent potential for artificial pellets to provide a viable alternative to provisioning live feed for the culture of paralarvae, minimal research in this area has been reported. The aim of this study was to evaluate whether artificial pellet size and shape affects the capture success of O. tetricus paralarvae. For this, the capture success of six different artificial pellets was tested in a crossed experiment for size (i.e., small, medium, or large) and shape (i.e., spherical, or rectangular). A total of 250 paralarvae aged 2 days post-hatch were individually observed for up to 5 min with size, shape and handling time of captured particles being recorded.
A total of 42 % (105/250) paralarvae captured one of the artificial pellets. The number of paralarvae capturing artificial pellets was not affected by the shape of the pellets, but there was a strong preference for smaller artificial pellets with 57 out of 105 paralarvae that captured any size of pellet selecting the small pellets (Fig. 1). The handling times ranged from 1 to 485 sec across all shapes and sizes of artificial pellets. The mean handling time was affected by the artificial pellet shape with shorter mean handling times of 13 ± 41 sec for rectangular pellets compared to 31 ± 97 sec for spherical pellets, regardless of their size.
Developing artificial pellets has the potential to greatly improve effectiveness and reduce associated costs of octopus paralarvae cultures, however, fundamental knowledge on their feeding behaviour is needed. The results from this study suggest that smaller pellets can lead to more captures and that size can affect the handling times. The next step will be to increase the palatability of the artificial pellets to increase handling times and thus consumption.