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The present study aimed to evaluate the effect of dietary linoleic acid to linolenic acid (LNA/ALA) ratio on growth performance, feed utilization, plasma metabolite profiles, and muscle and liver fatty acid profiles of juvenile tambaqui Colossoma macropomum. Six diets were formulated to contain incremental levels of corn oil (rich in LNA) from 0 to 7% at the expense of linseed oil (rich in ALA), resulting in dietary LNA/ALA ratios ranging from 3.1 to 26.9. A control diet including fish oil was also formulated. The trial lasted 49 days, and each diet was assigned to six groups of fish with an initial body weight of 43 g. At the end of the trial, dietary LNA/ ALA ratio did not affect growth performance, feed utilization, and plasma metabolites profile, except for HDL that was lower in fish fed the 3.8 LNA/ALA diet than the 3.1 or 5.0 LNA/ALA diets. Whole-body protein content was lower in fish fed the control and 3.1 LNA/ALA diets. Composition of triglycerides, glucose and protein of liver and muscle was unaffected by dietary treatments. Eicosapentaeneoic acid (EPA, 20:5n-3) plus docosahexaenoic acid, (DHA, 22:6n-3) content of muscle decreased with the increase of LNA/ALA ratio. Fish fed 3.9-5.6 LNA/ALA diet showed the highest concentration of muscle ARA (arachidonic acid, 20:4n-6) and EPA + DHA among vegetable oil diets, though lower than that of fish fed the fish oil based diet. In conclusion, dietary LNA/ALA ratio should range between 3.9-5.6 to produce fillets with high EPA, DHA, and ARA contents, thus improving the nutritional quality of tambaqui fillets for human consumers.

-The objective of this work was to evaluate the effect of inclusion of dietary glycerol in replacement to starch on the growth and energy metabolism of Nile tilapia juveniles. The experiment was carried out in a completely randomized design with four treatments (0, 5, 10, and 15% purified glycerol) and six replicates. Pelleted, isonitrogenous, and isocaloric diets were provided for 60 days. Growth performance parameters and muscle glucose and protein concentrations were not affected by dietary glycerol levels. The treatment with 15% glycerol presented higher levels of muscle and liver triglycerides. A quadratic effect of treatments on muscle and liver triglyceride concentrations was observed. The treatment with 0% glycerol presented higher hepatic glucose levels than the one with 15%. Treatments did not differ for concentrations of liver protein, as well as of plasma glucose, triglycerides, and protein. Treatments with 10 and 15% glycerol showed higher activity of the glucose-6-phosphate-dehydrogenase enzyme than the treatment with 5%; however, there were no significant differences in the hepatic activities of the malic and glycerol kinase enzymes. A linear positive effect of treatments was observed on the activity of the glycerol kinase enzyme in liver. Levels of glycerol inclusion above 10% in the diet of Nile tilapia juveniles characterize it as a lipogenic nutrient.Index terms: Oreochromis niloticus, alternative feed, carbohydrate, nutrition. Crescimento e metabolismo energético de juvenis de tilápia-do-nilo alimentados com glicerolResumo -O objetivo deste trabalho foi avaliar o efeito da inclusão de glicerol na dieta, em substituição ao amido, sobre o desempenho e o metabolismo energético de juvenis de tilápia-do-nilo. O experimento foi conduzido em delineamento inteiramente casualizado com quatro tratamentos (0, 5, 10 e 15% de glicerol purificado) e seis repetições. Dietas peletizadas, isonitrogenadas e isoenergéticas foram fornecidas por 60 dias. Os parâmetros de desempenho produtivo e as concentrações de glicose e proteína muscular não foram afetados pelos níveis de glicerol na dieta. O tratamento com 15% de glicerol apresentou maiores níveis de triglicerídeos musculares e hepáticos. Observou-se efeito quadrático dos tratamentos nas concentrações de triglicerídeos no músculo e no fígado. O tratamento com 0% de glicerol apresentou maiores níveis de glicose hepática do que o tratamento com 15%. Os tratamentos não diferiram quanto às concentrações de proteína no fígado, bem como de glicose, triglicerídeos e proteína no plasma. Os tratamentos com 10 e 15% de glicerol apresentaram maiores atividades da enzima glicose-6-fosfato-desidrogenase do que o tratamento com 5%; no entanto, não houve diferenças significativas nas atividades hepáticas das enzimas málica e glicerol quinase. Observou-se efeito linear positivo dos tratamentos na atividade da enzima glicerol quinase no fígado. Níveis de inclusão de glicerol acima de 10% na dieta de juvenis de tilápia-do-nilo o caracterizam como nutriente lipogênico....

Goblet cells (GCs) and endocrine cells (ECs) play an important role in intestine physiology, and few studies currently exist for Amazonian fishes. This study aimed to quantify the distribution of GCs and ECs producing cholecystokinin‐8 and neuropeptide Y, assessed by mucin histochemistry and peptides immunohistochemistry, in the intestine of two Amazonian species with different feeding habits Tambaqui (Colossosoma macropomum) and hybrid catfish (Pseudoplatystoma reticulatum × Leiarius marmoratus), an omnivore and carnivore, respectively. A systematic literature review correlating feeding habit and GC and EC distribution was also included to contribute to the comparative study. The results of this study provided novel information about the gut cells of Tambaqui and hybrid catfish. Both, GCs and ECs can be found sweeping the entire intestine of Tambaqui and hybrid catfish although the cells can be more concentrated in certain segments. The GCs and ECs in Tambaqui were more uniformly distributed in the midgut segments (T1, T2, and T3). Unlike, in hybrid catfish GCs were more concentrated in the hindgut (C4) and ECs mainly in the two midgut segments (C1 and C2) of hybrid catfish. Based on the comparison between Tambaqui, hybrid catfish, and other fishes in the literature review, we suggest that cell distribution can be partially explained by feeding habits, carnivorous vs. omnivorous.

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We report feeding studies on hybrid fish (carnivorous × omnivorous) to determine the interactions between protein sources during diet selection trials. We also examined behavioural rhythms (feeding and locomotor activity) using a self‐feeding system mounted with a feeder connected to an infrared photocell. Twenty fish (28.20 ± 0.05 g) were distributed in four aquariums (50 L each). First, the system was tested to evaluate the adaptation of catfish (Pseudoplatystoma reticulatum × Leiarius marmoratus) to self‐feeding (step I). During this 28‐day period, feeding and locomotor activity rhythms were recorded. In the second step, to analyse protein self‐selection, a group of 20 fish (19.10 ± 0.05 g) was released in the aquaria. The hybrid catfish were given free access to diets (soya bean meal protein (SP) vs. bovine liver protein (BP)) through two self‐feeders. The same procedure was used for (SP) vs. fish meal protein (FP). The catfish learned to activate the feeders to demand a daily feed amount equivalent to 1.8% of their body weight. The fish performed most of their actions (89.0% feeding activity and 94.1 0% locomotor activity) in the night. The diet choice by the catfish became clearer with a significantly lower intake of BP (0.37 g per 100 g body weight, 24.6%) vs. SP (1.06 g per 100 g body weight, 75.4%) and SP (0.61 g per 100 g body weight, 38.9%) vs. FP (0.91 g per 100 g body weight, 61.1%). These findings should be considered when discussing feeding behaviour, nutritional targets and protein sources for future aquaculture feeds.

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