Production optimisation of Tisochrysis lutea as a live feed for juvenile Sydney rock oysters, Saccostrea glomerata, using large-scale photobioreactors

Abstract

The aquaculture industry uses microalgae as a live feed for juvenile oysters in hatcheries to meet their nutritional requirements, including their need for several essential Poly Unsaturated Fatty Acids (PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The mass culture of microalgae is not only a major bottleneck for the production of juvenile oysters, but also a significant cost, accounting for 20–50% of hatchery operating costs. Currently, low biomass concentrations, high production costs and poor cultivation systems limit the quantity and quality of microalgae feed. This study focused on Tisochrysis lutea, a microalgae species commonly used in aquaculture, and we assessed the potential of photobioreactors with an improved light source and CO2 input to increase biomass production and improve biochemical composition of algal feed. Two photobioreactor systems were compared: the current industry set up (DPI) comprising fluorescent lighting and minimal CO2 input versus an optimized system utilising LEDs and increased CO2. Cultures of T. lutea were monitored over a 12-day growth period and harvested on day 14 for biochemical analysis. Final cell density was significantly higher in the optimized system relative to the conventional culture systems (6.2 × 106 cells / mL versus 3.7 × 106 cells / mL, respectively). The biochemical profile of T. lutea was not significantly different between the two photobioreactors systems. The algal biomass produced during this comparative experiment was used in a feeding trial on oyster spat, Saccostrea glomerata. Spat fed with algae produced in optimized vs conventional photobioreactors showed no significant difference in growth, but oyster spat fed with T. lutea grown in optimized photobioreactors did show a significant increase in their EPA content. Overall, our results contribute to our understanding of how altered culture conditions affect microalgal production and biochemical composition, and subsequently of oyster spat. This study further supports the potential of LEDs to reduce operating costs for oyster hatcheries but also to significantly improve microalgae yield with no negative effect on the condition of oyster spats production.