Fungal infections in marine animals, particularly pinnipeds, have seen a notable increase, often linked to compromised immune systems in captive environments. Trichophyton species, while common in terrestrial mammals, have sporadically caused dermatophytosis in pinnipeds. A South American sea lion (Otaria byronia) presented with Trichophyton benhamiae infection, marking the first such case in this species. Effective treatment combined oral terbinafine with topical ozonized oil, supported by silymarin for liver protection. Accurate fungal identification and sensitivity testing were key to the successful management and recovery of the patient.