Life cycle assessment of diets for gilthead seabream (Sparus aurata) with different protein/carbohydrate ratios and fishmeal or plant feedstuffs as main protein sources

Aquaculture is the best alternative to fulfil global fish demand, however it still relies heavily on fisheries-derived products for aquafeeds production. This study assesses and compares the environmental impacts of producing four experimental diets to gilthead seabream with different dietary protein (P) to carbohydrate (CH) ratios (P50/CH10 and P40/CH20). The diets were made either with fish meal (FM) or plant feedstuffs (PF) as main protein sources and fish oil (FO) or vegetable oils (VO) as lipid sources.

The functional unit used was 1 kg of experimental diet. The studied boundaries included aquafeed ingredients production (S1), compound aquafeeds production under laboratory conditions (S2), and transportation between S1 and S2 locations. The present study applied the Recipe Endpoint method, hierarchist version (V1.13; Europe recipe H/A). Background data was collected from ecoinvent database and related literature. For each aquafeed ingredient used, it was accounted either the agriculture production or fishery activities, the processing unit, and transportation between the production and processing locations. Ingredient mixing and processing was done at the Marine Zoology Station (MZS) located at Porto, Portugal. It was also taken into account the road transportation of aquafeed ingredients between a commercial company and the MZS.

Regardless of dietary protein source or P/CH ratio used, all diets had the same single score index. In agreement with several studies, S1 was the system with the highest environmental impact. On the other hand, S2 was the lowest environmental contributor step to all formulated diets, except for diet P50/CH10, where the lowest environmental impact was related with the aquafeed ingredients transportation to MZS. Fisheries-derived ingredients were the biggest contributors to environmental impact. In the hypothesis of replacing FO from Portuguese fisheries by-products by FO of Peruvian anchovy fisheries or by soybean oil (SBO), the environmental impact of the diets would be decreased, being the replacement by SBO the best environmental alternative.

There was highlighted a tendency for PF-based diets having lower environmental impact score when compared to the FM-based diets after both hypothetical replacements. Studying the replacement of by-products FO by Peruvian anchovy FO or by SBO allowed to emphasize the importance of adequate ingredients selection for reducing the environmental impact. As limitations of the current study it is important to mention: the use of pelletization as manufacturing process and the non-valorization of fish by-products as recycled aquafeed ingredients.