It is known that the level of dietary protein modulates the enzymatic activity of the digestive tract of fish; however, its effect at the molecular level on these enzymes and the hormones regulating appetite has not been well characterised. The objective of this study was to evaluate the effect of CP on the activity of proteases and the expression of genes related to the ingestion and protein digestion of juveniles of red tilapia (Oreochromis sp.), as well as the effects on performance, protein retention and body composition of tilapia. A total of 240 juveniles (29.32 ± 5.19 g) were used, distributed across 20 tanks of 100 l in a closed recirculation system. The fish were fed to apparent satiety for 42 days using four isoenergetic diets with different CP levels (24%, 30%, 36% and 42%). The results indicate that fish fed the 30% CP diet exhibited a higher growth performance compared to those on the 42% CP diet (P < 0.05). Feed intake in fish fed 24% and 30% CP diets was significantly higher than that in fish fed 36% and 42% CP diets (P < 0.05). A significant elevation of protein retention was observed in fish fed with 24% and 30% CP diets. Fish fed with 24% CP exhibited a significant increase in lipid deposition in the whole body. The diet with 42% CP was associated with the highest expression of pepsinogen and the lowest activity of acid protease (P < 0.05). The expression of hepatopancreatic trypsinogen increased as CP levels in the diet increased (P < 0.05) up to 36%, whereas trypsin activity showed a significant reduction with 42% CP (P < 0.05). The diet with 42% CP was associated with the lowest intestinal chymotrypsinogen expression and the lowest chymotrypsin activity (P < 0.05). α-amylase expression decreased with increasing (P < 0.05) CP levels up to 36%. No significant differences were observed in the expression of procarboxypeptidase, lipase or leptin among all the groups (P > 0.05). In addition, the diet with 42% CP resulted in a decrease (P < 0.05) in the expression of ghrelin and insulin and an increase (P < 0.05) in the expression of cholecystokinin and peptide yy. It is concluded that variation in dietary protein promoted changes in the metabolism of the red tilapia, which was reflected in proteolytic activity and expression of digestion and appetite-regulating genes.

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Protein is the most costly nutrient in fish feed, and while diets offered in the early stages of development typically have high levels of CP, they do not always correspond to the real requirements of the animals. Thus, research that seeks to learn the true nutritional requirements of fish is fundamental to improving commercial fish culture. The present study evaluated the protein requirements of Nile tilapia (Oreochromis niloticus) under larviculture. Fish performance, gene expression for digestive enzymes and their enzymatic activity and stress response to air exposure were analyzed. Four experimental diets differing in CP level were formulated: 30%, 36%, 42% and 48%. Fish larvae were fed the experimental diets during development and sampled 10, 20 and 30 days after the beginning of the experiment for performance, gene expression and enzymatic activity. At sampling time 30, stress resistance was also evaluated by means of an air exposure test. At sampling time 10, CP levels between 36% and 48% could be used for a better performance. During this period, pepsinogen expression was greater for 30% CP, intermediate for 42% and lower for 36% and 48%. After this initial period, diets of between 30% and 42% CP are recommended for better performance. At sampling time 20, gene expression for digestive enzymes and their enzymatic activity were similar for all diets tested. At sampling time 30, the diet of 42% CP induced both greater pepsinogen expression and pepsin activity. Survival after the air exposure test after 30 days of feeding was influenced by CP level in the diet, with the highest survival being for fish fed with 36% CP. Taken together, the present results demonstrate that dietary CP influences digestive enzyme gene expression and activity, and suggest that the best CP levels for Nile tilapia larviculture vary depending on larval stage.

While some studies have investigated the effects of dietary protein on the activities of protease in Nile tilapia, little information exists about these enzymes and hormones regulating appetite at the molecular level. Therefore, we investigated the performance, protease activities and expression of genes related to protein intake and digestion in juvenile tilapia fed with diets containing different levels of crude protein (CP): 25.14, 31.12, 36.60 and 42.05%. The fish were fed to apparent satiation three times a day for 65 days. The animal performance and the retention rates of protein and energy linearly decreased with an increase in dietary CP content. A positive quadratic effect of CP on pepsinogen was observed, although the acid protease activity was not affected. Trypsinogen and trypsin activity in the intestine presented similar patterns, showing a positive quadratic response to dietary protein levels. A linear increase in intestinal chymotrypsinogen expression was observed, but the activity of chymotrypsin showed a positive quadratic response. In addition, the expression of cholecystokinin (cck) and peptide yy (pyy) increased linearly with increasing CP. Dietary protein modulates the activity of alkaline proteases as well as the expression of these protease genes and hormones involved in appetite regulation. These changes can help expand our understanding of feed intake and digestion control, thereby improving feed formulations for this species.

Little information is available concerning liming and phosphate fertilization for grassland maintenance in Amazonia. The dry-weight yield of Brachiaria brizantha was assessed over three harvest periods as a function of top-dressing with lime and phosphorus. The experimental design consisted of fully randomized blocks with four replicates arranged in subdivided plots according to the sampling season (plots), phosphorus application rate (0, 30 and 60 kg ha -1 P 2 O 5 ) (subplots) and presence or absence of liming (sub-subplots). The grass was harvested by cutting 25 cm above the soil level, and the 0-to 5-, 5-to 10-, 10-to 20-and 20-to 40-cm soil layers were sampled 3, 9 and 13 months after liming. Topdressing with phosphorus and lime had no effect on the dry-weight yield, nutrient uptake or crude-protein percentage of the Brachiaria brizantha shoots. However, phosphorus and lime treatment reduced the soil acidity and increased the calcium, magnesium and phosphorus levels in the upper soil layers. 0-5, 5-10, 10-20 e 20-40

Objetivou-se estudar o efeito da mistura do adubo uréia com sementes de Brachiaria brizantha em sua germinação e vigor. As variáveis avaliadas foram teor de água, germinação, primeira contagem, condutividade elétrica, emergência e índice de velocidade de emergência. Houve efeito significativo em todas as variáveis. Com o transcorrer do tempo de mistura com o fertilizante, o teor de água e a condutividade elétrica das sementes aumentaram. Ao mesmo tempo, observou-se diminuição da percentagem de germinação, da primeira contagem, da emergência e do índice de velocidade de emergência. Concluiu-se que, quanto maior o tempo de contato das sementes de B. brizantha com o fertilizante uréia, menor será a taxa de germinação e vigor das sementes.

Carbohydrates represent a low-cost energy source compared to others, thus being critical for reducing the costs associated with producing formulated diets (Gao et al., 2010; Mohanta, Mohanty, & Jena, 2007). In addition, it is interesting to include non-protein energy sources such as carbohydrates in diets so that fish can direct most of the dietary protein to growth, improving animal performance (Bautista, 1986; Gao et al., 2010). It is important to emphasize that starch granules are essential for the extrusion of rations, because they expand when subjected to heat, pressure and moisture, which allows fluctuation in the diets (Laif & Kokini, 1991). Corn bran, generally used in animal feed, is considered to be one of the most palatable ingredients among cereals, being mainly made up of starch (Pastore, Gaiotto, Ribeiro, & Nunes, 2013). In general, herbivorous and omnivorous fish are more able to use carbohydrates