Glycolysis and gluconeogenesis in the liver of catfish fed with different concentrations of proteins, lipids and carbohydrates / Glicólise e gliconeogênese no fígado de jundiá alimentado com diferentes concentrações de proteínas, lipídeos e carboidratos

The activities of enzymes from a number of metabolic pathways have been used as a tool to evaluate the best use of nutrients on fish performance. In the present study the catfish Rhamdia quelen was fed with diets containing crude protein-lipid-carbohydrate (%) as follows: treatment (T) T1: 19-19-44; T2: 26-15-39; T3: 33-12-33; and T4: 40-10-24. The fish were held in tanks of re-circulated, filtered water with controlled temperature and aeration in 2000L experimental units. The feeding experiment lasted 30 days. The following enzymes of the carbohydrate metabolism were determined: Glucokinase (GK), Phosphofructokinase 1 (PFK-1), Pyruvate kinase (PK), Fructose-1,6-biphosphatase 1 (FBP-1). The activities of 6 phosphogluconate dehydrogenase (6PGDH) and glucose 6 phosphate dehydrogenase (G6PDH) were also assayed. The influence of nutrient levels on the enzyme activities is reported. The increase of dietary protein plus reduction of carbohydrates and lipids attenuates the glycolytic activity and induces hepatic gluconeogenesis as a strategy to provide metabolic energy from amino acids. The fish performance was affected by the concentrations of protein, lipid and carbohydrates in the diet. The greatest weight gain was obtained in fish fed diet T4 containing 40.14% of crude protein, 9.70% of lipids, and 24.37% of carbohydrate, respectively.(AU)

As atividades de enzimas das vias metabólicas têm sido utilizadas como uma ferramenta para avaliar a melhor utilização dos nutrientes e o desempenho dos peixes. No presente estudo, o jundiá foi alimentado com rações contendo diferentes concentrações de proteína bruta, lipídeos e carboidratos (%), da seguinte forma: tratamento (T) T1: 19-19-44; T2: 26-15-39; T3: 33-12-33; e T4: 40-10-24. Os peixes foram mantidos em tanques de recirculação, com água filtrada, temperatura controlada e aeração em unidades experimentais de 2.000L. O período experimental foi de 30 dias. Foram aferidas as atividades das enzimas glicoquinase (GK), fosfofrutoquinase 1 (PFK-1), piruvato quinase (PK) e frutose-1,6-difosfatase (FBP-1). Também foram aferidas as atividades da 6-fosfogluconato desidrogenase (6PGDH) e glicose-6-fosfato desidrogenase (G6PDH) da via das pentoses. É relatado que níveis de nutrientes influenciam as atividades enzimáticas das vias metabólicas. No presente estudo, o aumento da proteína da dieta e a redução de hidratos de carbono e lipídeos reduziram a atividade glicolítica e induziram a gliconeogênese hepática como uma estratégia para fornecer energia pelos aminoácidos. O desempenho dos peixes foi afetado pelas concentrações de proteínas, lipídeos e carboidratos na dieta. O maior ganho de peso foi obtido em peixes alimentados com dieta T4 contendo 40,14% de proteína bruta, 9,70% de lipídeos, e 24,37% de carboidratos, respectivamente.(AU)

Effect of different concentrations of protein on the digestive system of juvenile silver catfish / Efeito de diferentes concentrações de proteína sobre o sistema digestivo de juvenis de jundiá

Aspects of digestion in juvenile silver catfish Rhamdia quelen fed with four levels of protein (20, 27, 34 and 41%) were studied. The studied traits were digestive enzymes (nonspecific proteases, trypsin, chymotrypsin, amylase and lipase) and weight gain. The experiment lasted 60 days; 160 juvenile catfish with initial body weight of 32 grams were transferred to the experimental system of 500L tanks with re-circulated and thermostatized water. The average weight of silver catfish increased with dietary protein and 41% of crude protein (CP) was accepted as the best one. Gastric protease activity increases with the CP level. The intestinal alkaline protease reached the peak at 27% CP and the highest activities were observed in the anterior section of the gut (AS). The trypsin peak was observed at 34% CP in the AS and medium section of the gut (MS). Amylase and lipase activities were inverse to the dietary CP and the highest values were observed in AS. In conclusion, the digestive enzymes of catfishes are responsive to the dietary protein level. The dietary CP required for highest weight gain of juvenile silver catfish is 41%.

Foram estudados aspectos digestivos de juvenis de jundiá Rhamdia quelen alimentados com quatro níveis de proteína (20, 27, 34 e 41 %). As características estudadas foram enzimas digestivas (proteases inespecíficas, tripsina, quimiotripsina, amilase e lipase) e ganho de peso. O período experimental foi de 60 dias; 160 juvenis de jundiá com peso médio inicial de 32 gramas foram transferidos para um sistema experimental de tanques de 500L, com recirculação de água termostatizada. O peso médio dos jundiás aumentou com o teor de proteínas da dieta até 41% de proteína bruta (PB), valor esse considerado o melhor. A atividade de protease gástrica aumentou com o nível de PB. A protease alcalina intestinal atingiu o pico em 27% de PB e as maiores atividades foram observadas na secção anterior do intestino (SA). O pico de tripsina foi observado com 34% de PB na SA e na secção média do intestino (SM). As atividades de amilase e lipase foram inversas ao teor de PB, e os valores mais elevados foram observados na SA. Em conclusão, as enzimas digestivas de jundiá são responsivas ao nível de proteína da dieta. O teor mais alto de PB da dieta necessário ao maior ganho de peso em juvenis de jundiá é 41%.

Digestive enzymes and metabolic profile of Pseudoplatystoma corruscans (Teleostei: Siluriformes) in response to diet composition.

Digestive enzyme responsiveness to feeding and associated adjustments of metabolism can be used to derive nutritionally effective diet formulations. Juvenile pintado (Pseudoplatystoma corruscans) were fed different diets. After feeding, fish were killed and blood, liver and white muscle were collected to evaluate metabolites. Stomach along with anterior, middle and posterior intestine were sampled for enzyme analysis. Non-specific protease, trypsin, chymotrypsin, amylase and lipase were assayed. Crude protein (CP) did not induce proteolytic activity; highest protease activities were observed in the stomach. Amylase was higher in the stomach in fish feeding on diets containing 13-25% starch. Lipase activity was observed along the gastrointestinal tract, with the highest activities observed in the middle section. The metabolic profile of white muscle was not affected by CP. In contrast, some plasma and liver metabolites were altered concomitant with changes in the digestive enzymes. Amino acid catabolism was increased. Digestion in pintado was responsive to cornstarch, reflected in intermediary metabolism; proteolytic activities of the digestive tract seem to be sufficient to deal with large amounts of dietary protein. As a result, we are able to recommend a balance between protein and energetic compounds, such as lipids and carbohydrates, in the diet to optimize fish growth.