Neoplasia in Pisces is possibly related to pollution and, because of that, it has been used as a bioindicator of the existence of environmental carcinogens. This study aims to report a neoplasia exeresis in an adult, 105-gram goldfish (Carassius auratus auratus). It presented 1x1, 5x1, 3-cm rounded mass, dorsal to anal fin, with 3-year evolution. For the tumoral exeresis, three 12-liter tanks of water were used, heated to 26°C, and 90-watt pumps with capacity to pump 120 liters of water per hour. For the induction of anaesthesia, isoflurane diluted in water (1.8 ml/L^-1) was used until cardiorespiratory depression. Subsequently, the fish was placed on a moist surgical foam table, in addition to one of the pumping systems with oxygenated water and the same anaesthesia (0,9 ml/L^-1) recirculation. During the procedure, the patient was kept intubated with a semiclosed guidewire system for the oxygenation of the water in the gills (2 L/min^-1). The skin incision was performed with a scalpel followed by debridement with rounded point scissors, and hemostasis was obtained by digital pressure. The nodule was sent to histological evaluation, which resulted in leiomyoma. Administered postoperatively was 0,2 mg/kg^-1 meloxicam IM, SID during three days, and enrofloxacin 0,3 ml/L^-1 diluted in the fish tank once a day, for five days. Currently, the animal is without recurrence; it has only a scar. Surgical excision of neoplasms in fish, when possible, presents a good prognosis, provided that it is performed correctly and respects the proper modifications in the surgical, anaesthetic, and therapeutic protocols.