Effect of Dietary Digestible Protein Levels on Muscle Growth and Oxidative Stress in Amazonian Pintado (Pseudoplatystoma reticulatum × Leiarius marmoratus).

Abstract: Simple Summary In fish farming, protein is the most expensive macronutrient in the diet. Research on the physiology of fish nutrition has focused on the relationships between nutrient intake and animal development and metabolism. The dynamics of protein metabolism are influenced by the body's nutrient needs and dietary protein and energy intake. The Amazonian Pintado, a crossbred hybrid of Pseudoplatystoma reticulatum x Leiarius marmoratus, is farmed due to its growth rate, feed conversion efficiency, carcass yield, and absence of intramuscular bones. This study aimed to evaluate the effects of dietary digestible protein levels on muscle growth dynamics and oxidative stress in the white muscle of Amazonian Pintado. The results revealed that high dietary levels of digestible protein, despite increasing protein and free amino acid concentrations in the muscle, restrict muscle hypertrophy and increase tissue exposure to oxidative damage in Amazonian Pintado farming.Abstract This study aimed to evaluate the effects of dietary digestible protein levels on the growth dynamics and oxidative stress status of white muscle fibers in Amazonian Pintado (Pseudoplatystoma reticulatum x Leiarius marmoratus). Four hundred and fifty-five juveniles of Amazonian Pintado were fed diets containing varying digestible protein levels (225, 250, 275, 300, 325, 350, or 375 g kg-1) for 75 days. At the end of the experiment, the fish were fasted for 24 h, anesthetized, and euthanized to obtain muscle samples. The linear and quadratic effects of dietary digestible protein levels on white muscle fiber diameter, metabolite concentrations, and oxidative stress were assessed. The results revealed that increasing dietary digestible protein levels linearly raised the concentrations of free amino acids and total proteins in muscle tissue but also led to elevated levels of TBARS, indicating increased oxidative stress. Notably, the average area of muscle fibers with a cell area greater than 1133 mu m2 decreased, reflecting restricted muscle hypertrophy, whereas glycogen and glucose levels also declined. These findings suggest that although high dietary digestible protein enhances protein and free amino acid concentrations in muscle tissue, it may compromise muscle hypertrophy and increase oxidative damage in Amazonian Pintado, underscoring the complexity of optimizing diet formulation.