With the increasing prevalence of high-fat diets (HFD) in aquaculture practices, the detrimental effects of HFD on farmed fish have garnered significant attention. Creatine has emerged as a promising green feed additive for aquaculture species; however, its potential role in mitigating the negative impacts of HFD remains poorly understood. To address this knowledge gap, the present study was designed to investigate the protective effects of dietary creatine supplementation on HFD-induced hepatic lipid metabolism disorders and muscle quality deterioration in juvenile grass carp (). Three experimental diets were formulated: a control diet (5.20% lipid, control), a HFD (8.11% lipid, HFD), and a HFD supplemented with 2% creatine (HFD + creatine). Juvenile grass carp (initial weight: 4.12 ± 0.02 g) were randomly allocated into nine 300-L indoor tanks and fed the experimental diets for 8 weeks. The key findings of this study revealed that (1) Dietary creatine supplementation significantly ameliorated the adverse effects of HFD on growth performance and feed utilization efficiency in juvenile grass carp. (2) Creatine supplementation improved muscle quality parameters in juvenile grass carp. (3) Dietary creatine attenuated HFD-induced hepatic lipid accumulation through enhanced fatty acid -oxidation, which was mediated by mfn2-dependent mitochondrial fusion. Notably, this study elucidates a novel molecular mechanism whereby creatine activates mitochondrial fusion through the binding of transcription factor to specific sites on the mitofusin 2 (Mfn2) gene promoter. To our knowledge, this is the first comprehensive investigation from a multi-organ/tissue perspective combined with mitochondrial dynamics analysis, providing valuable insights for developing effective nutritional strategies to counteract HFD-induced adverse effects in farmed fish through creatine supplementation.