Atlantic Salmon Insulin-like Growth Factor 1 (IGF-1) is a peptide growth factor that plays a central role in regulating growth, development, and metabolic processes in Atlantic salmon (Salmo salar). IGF-1 is produced primarily in the liver in response to growth hormone stimulation and circulates in the bloodstream bound to insulin-like growth factor binding proteins (IGFBPs), which regulate its stability, transport, and bioavailability. It is also expressed locally in multiple tissues including muscle, bone, gill, and intestine, where it acts through autocrine and paracrine signaling. Atlantic salmon IGF-1 binds to the insulin-like growth factor 1 receptor (IGF1R), a transmembrane tyrosine kinase receptor that activates intracellular signaling pathways such as PI3K–AKT and MAPK, regulating cell proliferation, differentiation, protein synthesis, and survival. In Atlantic salmon, IGF-1 plays a critical role in somatic growth, skeletal and muscle development, and metabolic regulation, and it is also an important mediator of smoltification—the physiological transition that prepares juvenile salmon for seawater adaptation. Due to these functions, IGF-1 is widely studied in fish physiology, aquaculture, and developmental biology, where circulating IGF-1 levels are commonly used as a biomarker of growth performance, nutritional status, and endocrine regulation of growth in salmonids.