Abstract
Triphenyl phosphate (TPhP) is a widely used organophosphate flame retardant and plasticizer, raising concerns over its health impacts. This study examined the effects of embryonic TPhP exposure on axial skeletal development and metabolism in medaka (Oryzias latipes), a vertebrate fish model relevant to human bone biology. Medaka embryos were exposed to 1 µM TPhP and assessed through early larval stages. TPhP impaired vertebral ossification, causing shortened centra and reduced cartilage in the caudal complex, alongside disrupted distribution of osteoblast-lineage cells. Key osteogenic genes were significantly downregulated at 14 days post fertilization, and transcriptomic analysis revealed altered mitochondrial pathways linked to skeletal disorders. Functionally, TPhP-exposed larvae showed reduced caudal fin regeneration and decreased metabolic rate and oxygen consumption, consistent with mitochondrial dysfunction. These findings indicate that TPhP disrupts bone development and metabolism by affecting osteoblast differentiation and mitochondrial regulation, highlighting the value of small fish models for studying environmental toxicants and bone metabolic disease risk.