Brazilian freshwater fish production has increased over the years (FAO, 2018). Brazilian native species of the genus Rhamdia have great potential for fish farming because they can withstand cold winters and grow fast in the summer. These characteristics make them suitable for fish production in the South of Brazil (Diemer et al., 2012).The catfish Rhamdia voulezi and Rhamdia branneri are endemic from the Iguaçu River basin and belong to the class Osteichthyes, the order Siluriformes and the family Heptapteridae (Boockmann & Guazzelli, 2003).Studies on the nutrition of these species are essential to estimate their nutritional requirements at different life stages. A variety of by-products have been studied and tested as alternative feed sources, including crude glycerol, a by-product derived from biodiesel production. Moreover, crude glycerol has been tested in recent years as a substitute energy source to corn in the diets of poultry, pork and fish (Shields, Van Heugten, Lin, Odle, & Stark, 2011).Studying the inclusion of glycerol in the nutrition of post-larvae (R. voulezi and R. branneri) is important for enabling the use of an alternative energy source in diets, with a focus on reducing the costs of feed (Abdalla, Silva Filho, Godoi, Carmo, & Eduardo, 2008). This study aimed to evaluate the replacement of corn with crude glycerol as an energy source on performance and body composition of R. voulezi and R. branneri post larvae.Two experiments were carried out simultaneously at the Laboratory of Technology for Reproduction of Cultivated Aquatic Animals (Latraac) of Unioeste, Campus Toledo, during 60 days. The Rhamdia voulezi and Rhamdia branneri with 0.01 ± 0.001 g (SD) were randomly distributed into five treatments with three replicates each, at a density of 5 post larvae/L, totalling 30 tanks of 60 L each.The experiment was carried out in a water recirculation system with biofilters. The water temperature and dissolved oxygen were measured twice a day, and the pH was measured weekly. Water physicochemical parameters were within normal limits for the studied species (Baldisserotto & Radunz Grandson 2004), with mean temperatures of 26 ± 1.1°C for R. voulezi and R. branneri respectively. The mean dissolved oxygen and the standard deviation were 7.60 ± 0.8 mg/L for R. voulezi and 8.04 ± 0.8 mg/L for R. branneri, whereas the mean pH was 7.67 ± 0.06 for R. voulezi and 7.82 ± 0.05 for R. branneri.The treatments consisted of five inclusion levels of crude glycerol (0, 2.2, 4.4, 6.6 and 8.8%). The animals were fed until apparent satiation three times per day. Tanks were siphoned every morning to remove faeces and feed residues. Crude glycerol was supplied by Biodiesel Sector of Southern Brazil and Trade S/A (BSBIOS), Passo Fundo -RioGrande do Sul, Brazil. Five isoproteic and isoenergetic diets containing 38.6% and 3,600 kcal/kg were formulated (Table 1). The digestibility values used for diet formulation were proposed by Boscolo, Hayashi, and Meurer (2002) and Meurer, Hayashi, and Boscolo (2003).At the end of the exp...
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