Skeletal muscle in the fish forms the most of body mass and the growth occurs by hypertrophy and / or hyperplasia of the muscle fibers, processes that vary with the species, stage of development and nutritional status. The development, growth and the maintenance of muscle phenotype involve the activation or inhibition of signaling pathways responsible for controlling the activity of the anabolic and catabolic pathways in muscle tissue. Based on this information, studies that seek to elucidate the signaling pathways, the molecular and cellular mechanisms involved in the control of muscle mass are fundamental to a better understand the real contribution of these pathways in muscle growth and during situations that a change occurs in the homeostasis between anabolic and catabolic states, such as food restriction and refeeding conditions. The aim of this study is to evaluate in juvenile of pacu (150g) submitted a period of fasting (10 days) and refeeding of 03 days: (a): the morphology and morphometry of muscle fibers and (b) gene expression of the components of the pathways related to anabolism and catabolism; gene expression of the transcriptional factors of the MyoD family. The fish will be cultivated in water tanks of 0.5 m³ with distinct recirculation systems. Samples of red and white muscle (n = 10) will be collected a every 2 days of fasting and 6 hours of refeeding. The expression of selected genes will be performed by Real Time Polymerase Chain Reaction after Reverse Transcription (RT-qPCR) and for the muscle fiber morphometry we will use cryostat cross-sections stained with hematoxylin-eosin. The data obtained will be subjected to appropriate statistical analysis after the completion of tests of normality and homoscedasticity.
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