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.

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The need for a sustainable aquaculture is increasing the use of plant ingredients in replacement to fishmeal and fish oil in diets for tambaqui Colossoma macropomum, which is leading to not detectable levels of docosahexaenoic acid (DHA) in its flesh. We evaluated the effect of a finishing plant diet supplemented with 5% of microalgae meal from Schizochytrium sp. (MD) on tambaqui growth, on proximal composition and fatty acid content of its flesh, comparing it to a non‐supplemented diet. One hundred and sixty‐two fish (489.67 g) were distributed into six tanks (2,000 L) and fed the experimental diets for a 90‐day period. Three fish per tank were euthanized for analyses every 15 days. The MD did not affect the growth and proximal composition of fish flesh. The MD increased the DHA content (from 14.81 to 38.60 mg/g of lipids) and the n‐3:n‐6 ratio (from 0.16 to 0.51) in the flesh of fish, beginning on the 15th day and reaching the highest DHA content on the 71st day (39.81 mg/g of lipids). We recommend C. macropomum to be fed with a finishing diet supplemented with microalgae meal for 71 days before slaughter to improve the DHA content and n‐3:n‐6 ratio in the flesh.

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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