From Gross Lesions to <scp>3D</scp> ‐ <scp>CT</scp> : A Multimodal Approach to Diagnosing <i>Myxobolus lentisuturalis</i> Infections in Ornamental Goldfish ( <scp> <i>Carassius auratus</i> </scp> ): 2023–2024

Goldfish (Carassius auratus) are among the most widely cultured ornamental fish. Skeletal deformities and muscular lesions have been reported in cyprinids, but their aetiology and pathology remain unclear. Advanced diagnostic tools, including radiography, ultrasonography and computed tomography, provide valuable insights when combined with histopathology. This study aimed to characterise clinical, radiological, ultrasonographical, computed tomographical and histopathological features of goldfish with hump-like lesions and muscular cavities caused by Myxobolus lentisuturalis in two farms, and to compare disease manifestations between populations using advanced imaging plus histology. From January 2023 to March 2024, ~10% of fish from two commercial goldfish farms in Tehran Province showed clinical signs. The first group had only hump-like lesions behind the head without exudate, whereas the second also had large muscular cavities with whitish exudate. Thirty goldfish (15 per farm) were sampled. Digital radiography, B-mode ultrasonography, computed tomography (CT/3D-CT), wet smears and histopathological sections were prepared. In the first stock, bilateral crescent-shaped humps containing Myxobolus lentisuturalis spores were observed, with radiographs revealing increased lesion density and obscured swim bladder margins, and ultrasonography indicating muscular hypertrophy with elevated echogenicity. In the second stock, hump-like lesions accompanied by exudates, cavitations, and severe muscular dystrophy were detected, supported by radiographic and CT evidence of deformity, cavitation, and asymmetry. This study demonstrated that M. lentisuturalis infection in goldfish can present with distinct clinical and pathological manifestations, ranging from localised hump-like lesions to extensive muscular cavitation and deformity. The integration of radiography, ultrasonography, CT imaging, and histopathology provided a comprehensive diagnostic approach for characterising disease progression. These findings highlight the importance of advanced imaging modalities in ornamental fish medicine and contribute to a better understanding of myxozoan-associated lesions in cyprinids.