Valorisation of agricultural residues into Thauera sp. Sel9 microbial proteins for aquaculture

Unconventional protein sources are necessary to tackle the increasing demand for food. Microbial proteins (MP) are an alternative source of proteins for feed or food, suitable as feed for aquaculture. Substituting fishmeal with MP obtained from agricultural wastes could reduce the environmental burden of aquaculture and help with waste management. In this study, pure culture MP from the PHA-producer Thauera sp. Sel9 were obtained from agricultural residues (agro-zootechnical digestate and pasta industry leftovers). The produced MP was used in feeding tests with the model fish zebrafish (Danio rerio) to assess potential toxic effects and evaluate overall fish health. The obtained MP was rich in protein (59.5 % w/w over TS) and PHAs (15.0 %) and comprised all fish essential amino acids. The chemical scores and essential amino acid index confirmed the excellent quality of the MP. The feeding tests with 50 % feed substitution with MP resulted in survival rates (80–88 %) comparable to the control group (78 %), with only 100 % MP showing increased mortality. Thauera MP obtained from agricultural residues has the potential to become a partial fishmeal substitute in fish-farming.