Feed Utilisation of <i>Chlorella Vulgaris</i> Cultivated with Aquaculture Effluent

Abstract

The combination of aquaculture and microalgae cultivation with aquaculture effluent is a promising strategy, being economically and ecologically sustainable. This study explored the growth of Chlorella vulgaris and unintentionally cultivated microalgae with and without CO 2 injection. The microalgae were cultivated with aquaculture effluent at the rearing temperature of coho salmon (18.5°C). In addition, we conducted batch and semi-continuous cultivations with unsterilized aquaculture effluent, demonstrating the dominance of C. vulgaris. Carbon was the limiting factor for microalgal growth in the effluent, and CO 2 injection effectively enhanced the C. vulgaris growth. The highest percentage of C. vulgaris (over 99% of the total microalgal cells) was achieved by batch mode, by inoculating different amounts of C. vulgaris cells. This abundance resulted in the complete consumption of PO 4 3− in the effluent. A dominant semi-continuous cultivation of C. vulgaris, containing 82 mg/L of suspended solids, was achieved in 23 days. However, the occurrence of zooplankton grazing resulted in a sharp decrease of C. vulgaris. The cultivated C. vulgaris presented a high total content of amino acids, and the amino acid composition suggested that they could be efficiently used as protein sources for coho salmon.