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 aim of this study was to evaluate the survival and growth of Arapaima gigas larvae reared in slightly salinized water. Pirarucu larvae (183.1 ± 41.2 mg and 3.4 ± 0.3 cm) were stocked in PVC tanks (20 L; n = 4; 40 larvae per tank) in a static system. A. gigas larvae were reared in increasing levels of salinized water (0, 1, 2, 3 and 4‰) for a period of 15 days. Fish were fed six times a day with Artemia nauplii (2,900 nauplii per larvae per meal in the beginning). The salinized water increased by at least four times the Artemia nauplii lifespan, which prolonged the time of live food supply to Arapaima larvae. Pirarucu larvae kept in freshwater presented the lowest values in weight gain, final weight and survival. Larvae reared in water with 4‰ of salinized water showed the highest final weight. Slightly salinized water enhances the growth and survival of A. gigas larvae and it can be a simple practice with low cost that can be applied in the routine of pirarucu larviculture.

Black soldier fly (BSF, Hermetia illucens) meal is a prominent ingredient to keep up with the increasing demand of protein sources for aquafeeds. This study evaluated the digestibility of defatted BSF larvae meal (DBSFL) by indirect method, growth performance, haematological parameters, and carcass composition of tambaqui (Colossoma macropomum) fed diets containing DBSFL. The apparent digestibility coefficient of protein from DBSFL was 84.2%, corresponding to 42.9% of digestible protein. For the feeding trial, juvenile tambaqui (3.25 ± 0.01 g) were randomly distributed in 18 experimental units (100 L; n = 3; 27 fish/tank) in a recirculation system. Fish were fed to apparent satiation for 60 days with isoproteic and isocaloric diets containing 0%, 6%, 12%, 18%, 24% or 30% of DBSFL meal. At the end of feeding trial, fish length and weight were recorded; blood samples were drawn from caudal vein of three fish per tank, and three fish from each replicate were euthanized for analysis of carcass proximate composition. The inclusion of up to 30% DBSFL meal did not impair tambaqui growth performance and fish body composition. The blood cholesterol level of the fish fed diet with 30% DBSFL inclusion was higher, but within the limits recorded for that species. DBSFL meal seems to be an interesting and safe protein source for tambaqui farming. The use of this ingredient as protein source can encourage the circular economy by promoting environmental sustainability.

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The present study evaluated the effects of commercial guarana (Paullinia cupana) powder as a growth-promoter and natural antioxidant supplement in aquafeeds. In Experiment 1, fish were fed with graded levels of guarana powder (0, 1.25, 2.5, 5 and 10 g/kg) during 60 days. Growth, hemato-immunological and biochemical performance were evaluated in healthy fish and in fish after infection by Aeromonas jandaei. In Experiment 2, the supplemented feed was stored for 90 days, in which tests were carried out regarding the quantity of phenolic compounds and the inhibition of lipid peroxidation. As a result of Experiment 1, fish fed guarana-supplemented diets and infected by A. jandaei presented better parameters of leukocyte respiratory activity, total proteins, globulin, albumin, alanine aminotransferase (ALT), leukocytes, lymphocytes, neutrophils, monocytes and thrombocytes. As a result of Experiment 2, levels of phenolic compounds were not altered (p > 0.05) by the guarana-supplemented diets. An increase in the concentration of malondialdehyde (MDA) and a lower oxygen radical absorbance capacity (ORAC) was observed in the fish fed diets with the highest level of guarana supplementation. As conclusion, guarana did not impair productivity and revealed a possible cytoprotective and hepatoprotective effect in fish infected by A. jandaei. Therefore, guarana seems to be an interesting additive to be included at levels of up to 1% in special feeds to be used prior to stressful situations in aquaculture. Additionally, guarana had no protective effect against lipid peroxidation and showed a pro-oxidant effect in diets with higher supplementation levels.