Fish viscera can be an important source of protein and energy for aquafeed, and its use contributes to circular aquaculture. The aim of this study was to produce acid and fermented silage from fish viscera to determine their nutritional value and the apparent digestibility coefficient of nutrients and energy for juvenile tambaqui (Colossoma macropomum). An acid silage and three fermented silages with different sources of carbohydrates (molasses, wheat bran, and cassava waste) were produced with 0.25% sorbic acid as an antifungal in the formulation. Silages presented an average of 55% dry matter, 62.9% lipids, and 12% crude protein. Leucine and lysine predominated as essential amino acids in the acid silage and fermented silages. Fish viscera silages presented EPA and DHA content from 5.4 to 17.8 and 1.7 to 8.9 mg.g⁻¹ of lipids, respectively. The apparent digestibility coefficient (ADC) (indirect method) was above 82% for gross energy for all the formulations. The ADCs for protein were similar for the fermented silages, with a maximum 92% level for the fermented wheat bran silage. The bioconversion of fish viscera into silage makes it an energy ingredient for aquafeed that is well digested by tambaqui juveniles.

The objective of this work was to analyze the proximate and fatty acid composition of the dorsal and ventral muscles of wild pirarucu (Arapaima gigas) captured from a Brazilian Amazonian lake. Dorsal and ventral muscles were dissected out, freeze-dried, vacuum-packed, and had the proximate and fatty acid composition analyzed. Ash, total proteins, and lipids were inversely proportional to moisture and had higher levels in the ventral muscles. Twenty-seven fatty acids were quantified in both muscles without significant differences between them, except for the heneicosylic, palmitoleic, γ-linolenic, and dihomo-γ-linolenic acids. Saturated and monounsaturated fatty acids were predominant in both muscles. The eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids were quantitatively similar: 9.25 (dorsal) to 10.14 (ventral) and 8.50 (dorsal) to 10.63 (ventral) mg g^-1 of total lipids, respectively. The EPA+DHA content of the dorsal and ventral muscles were 113.25 and 165.78 mg 100 g^-1, respectively. The ratios of polyunsaturated/saturated (0.54 and 0.59 for the dorsal and ventral muscles, respectively), n-3/n-6 (0.20 and 0.21), and hypocholesterolemic/hypercholesterolemic fatty acids (1.41 and 1.45) ratios, as well as the atherogenicity (0.59 and 0.53) and thrombogenicity (1.02 and 0.94) indices, indicate that pirarucu muscle is a good dietary source of EPA+DHA, and its nutritional lipid quality can be beneficial for human health.