Regulatory mechanisms of muscle growth and metabolism in fish: modulatory by nutritional status, diet composition, exercise and muscular regeneration

[eng] With the most absolute purpose of understanding what the “simple” concept of “growth regulation” implies, the present thesis is a compilation of original works that aims to deepen in how the growth and metabolism of fish, and most concretely, its muscle, behaves in different metabolically challenging conditions. Hopefully, the knowledge generated in these works and integrated in this multi-perspective thesis, can contribute to somehow help to improve the Aquaculture sector in the Mediterranean Sea and abroad. This ambitious goal is structured in different objective: 1) To establish the regulation of the ghrelinergic system in bream through the fasting and feedback model: a) Characterization of the sequences of Preproghrelin, Ghsr1a and Ghsr1b in gilthead sea bream (Article 1). b) Characterizing Preproghrelin and its two receptors in acute and long-term feeding responses and its interaction with the Gh/Igf1 axis (Article 1). 2) To deepen in the beneficial effects of exercise on growth and its modulation through changes in the dietary protein/lipid ratio: a) Determining how this dietary modification alters different growth parameters, muscular proximal composition and reserves turnover (Article 3). b) Determining how the mitochondrial proteins in red and white muscle and in the liver respond to this dietary modification in order to infer changes in the nutritional efficiency and growth improvement (Article 3). 3) To make a comparative study about the response of the main musculoskeletal growth regulation systems under two different challenging experimental models, the fasting and refeeding and the sustained exercise under two different diets. a) Studying the gene expression of specific proteins of the ontogenetic and growth pathways (myogenesis and osteogenesis), as well as the degradation pathways (proteolysis and osteoclastogenesis) in white muscle and bone (Articles 2 and 4). b) Determining its effects on white muscle growth (myogenesis/proteolysis balance) and meat quality (Article 4). 4) To complete the characterization of the new Myomaker and Myomixer fusogens in rainbow trout and gilthead sea bream and its involvement in the myogenic process in vivo and in vitro and in the in vivo muscle regeneration. a) Characterization of the sequence of Myomixer in rainbow trout (Article 5) and Muomaker and Myomixer in gilthead sea bream (Article 6). b) To study the involvement of Myomaker (in gilthead sea bream) and Myomixer (in rainbow trout and gilthead sea bream) in the myogenic process in vivo and in vitro as well as during the muscle regeneration in vivo (Article 5 and 6)