Using Discarded Shellfish From Aquaculture as Food for Rearing Juvenile Gloomy Octopus, Octopus tetricus

ABSTRACT A key bottleneck in the development of octopus aquaculture is the absence of formulated feeds that are readily consumed and fulfil their nutritional requirements. Until efficacious formulated feeds are developed, sustainably‐sourced natural seafood diets provide a potential viable alternative for octopus aquaculture. To investigate this alternative, this study measured feed intake, growth and biochemical composition of juvenile Octopus tetricus when fed bivalves discarded from shellfish aquaculture. Three dietary treatments were tested over 56 days: (1) whole thawed bivalves (natural feed), (2) bound pellet made from chopped bivalves bound with gelatine and transglutaminase (GO pellet) and (3) bound pellet made from chopped bivalves and krill meal, bound with gelatine and transglutaminase (GOK pellet). Overall, the mean specific feeding rate (wet weight) among octopus was highest in the natural feed (12.1 ± 1.5% BW day −1 ) regardless of time, indicating inferior palatability in the two bound pelleted feeds. Mean specific growth rates were higher from Day 0–28 (1.8 ± 0.2% BW day −1 ) than from Day 29–56 (1.0 ± 0.2% BW day −1 ) independently of dietary treatment. Mean feed efficiency (23.3 ± 3.3%) and feed conversion (5.5 ± 0.9) were similar among treatments for the whole experiment. The biochemical profile of octopuses was similar among treatment aside from a 30% increase in lipid content in arm tissue for octopuses fed with the natural feed. The results show that discarded bivalves from commercial aquaculture are an effective feed for juvenile O . tetricus providing fast growth and good feed conversion. While consumption and growth were reduced with the bound pelleted feeds, these wet seafood‐based feeds hold promise as a route to begin to develop formulated feeds for octopuses while utilising an otherwise wasted resource, especially if the palatability of these bound pelleted feeds can be improved.