Dietary creatine promotes creatine reserves, protein deposition, and myofiber hyperplasia in muscle of juvenile largemouth bass (Micropterus salmoides)

Creatine can increase muscle mass, enhance performance, prevent disease -induced muscle atrophy, and improve overall cellular energy. This study investigated the effects of creatine as a feed additive on muscle growth and intrinsic molecular regulation mechanism in largemouth bass (Micropterus salmoides). Seven diets supplemented with different concentrations of creatine (0%, 0.1%, 0.25%, 0.5%, 1%, 2%, and 4%) were fed to juvenile largemouth bass (4.5-5.1 g) for eight weeks. Dietary creatine significantly increased body weight and body length, and reduced feed conversion ratio. High-performance liquid chromatography analysis revealed that dietary creatine addition notably increased creatine and phosphocreatine levels by 19.94% and 16.54% in the muscle of largemouth bass, respectively. Histological observation showed that dietary creatine significantly increased the total muscle fiber number and decreased the mean muscle fiber diameter. The Western blot results indicated that creatine ingestion significantly increased the protein level of MyoD1 in the muscle and promoted muscle fiber hyperplasia. In addition, dietary creatine also contributed to mTOR-S6K/4EBP1-mediated protein synthesis by maintaining AMPK alpha Thr172 dephosphorylation and AKT Thr308 phosphorylation. Moreover, the protein levels of the muscle -specific E3 ligases Atrogin1 and Murf1 responsible for ubiquitination degradation exhibited no significant change after feeding with creatine in largemouth bass. Overall, our data showed that creatine as a feed additive increased creatine and phosphocreatine contents, thus promoting muscle protein deposition and myofiber hyperplasia, eventually elevating growth performance and feed utilization efficiency in juvenile largemouth bass. The regression analysis of weight gain rate, specific growth rate, and feed conversion ratio determined 0.46%-0.54% creatine concentration range as optimal supplementation concentration for the culture of juvenile largemouth bass.