Hidden Nutrient Resource: Repurposing Fish Consumption Waste for Sustainable Aquaculture

We determined the proximate composition, and fatty acid and amino acid profiles of the waste (head and viscera) from European anchovy (Engraulis encrasicolus), rainbow trout (Oncorhynchus mykiss), gilthead seabream (Sparus aurata), and European seabass (Dicentrarchus labrax) to evaluate their potential use in aquafeeds. The samples were collected from a local fish retailer once a week, 10 times in total between December 2019 and February 2020. The protein content did not show significant variations among species, averaging 12.4%. However, lipid, ash, and moisture exhibited significant differences among species (P < 0.05). The lowest and highest lipid contents were found in European anchovy (17.0%) and European seabass (29.9%), respectively. Gilthead seabream had a similar ash level (5.1%) to European seabass, but significantly higher level than European anchovy and rainbow trout. Fatty acid composition of the waste significantly varied among species (P < 0.05). European anchovy waste had a significantly higher saturated fatty acid (SFA) content (37.0%) than the other three species. The most abundant polyunsaturated fatty acids (PUFAs) in rainbow trout, gilthead seabream, and European seabass were linoleic acid (LA; 18:2n-6) and linolenic acid (LNA; 18:3n-3), whereas the predominant PUFAs in European anchovy were eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). Amino acid profile significantly differed among species (P < 0.05). The most abundant essential amino acid (EAA) in European anchovy, rainbow trout, and European seabass was leucine, while lysine was the predominant EAA in gilthead seabream. However, total EAAs and non-essential amino acids (NEAAs) contents did not change among the species, averaging 41.6 and 56.7 g/100 g protein, respectively. The results showed that unutilized fish consumption waste from small local markets possesses a favorable nutritional profile and can serve as a promising alternative raw material for the sustainable aquafeed industry.