Various cultures of microalgae are used in many industries such as the formulation of feed, wastewater treatment, fertilizers, and biofuel production. Isochrysis galbana and Tetraselmis suecica are commonly used microalgae in bivalve cultivation systems. In these systems, microalgae supply has been estimated to run at almost half of the bivalve hatchery operating costs and is prone to be unreliable due to easy contamination leading to crashing. Nonetheless, standard algae cultures are much less concentrated since the cells are free-swimming. Concentrated algae cultures are significant for feed management and storage in aquaculture since they allow more cells to be harvested. We aimed to standardize a protocol for concentrating algae cultures via freshwater overlays at 8, 16, 24, and 32 ppt.
I. galbana and T. suecica were grown in 200mL bottles that were inoculated with 5mL of established stock. Cell counts were collected using a hemocytometer to create growth curve charts and establish when the stationary phase was reached. I. galbana took 7 days to reach the stationary phase while T. suecica took 6 days. After the stationary phase counts were collected, freshwater overlays were introduced.
I. galbana had 3 layers form while T. suecica had only 2 layers form. Figures 1 and 2 show it is best to harvest concentrated algae after 24 hours because at 48 hours the concentration decreases. Overall, 24 ppt seems to be the most suitable to achieve the highest concentration with freshwater overlays. In summary, freshwater overlays hold promise for concentrating algae.