Aquatics Multisystemic Neoplasia Study Guide

Overview and Clinical Importance

Neoplasia in fish represents an important multisystemic disease category that is increasingly recognized in aquatic veterinary practice. Fish develop tumors similar to those found in higher vertebrates, with both benign and malignant forms occurring across multiple organ systems. Neoplastic diseases occur with some frequency in both wild and captive fish populations, with the skin being the most commonly affected site. Among ornamental fish, koi (Cyprinus rubrofuscus) and goldfish (Carassius auratus) are the most frequently diagnosed species with neoplasia, representing approximately 18.5% and 12.5% of all fish cancer cases respectively.

In bony fishes, connective tissue neoplasms such as fibroma and fibrosarcoma are among the most common tumor types. The mean age at presentation for fish with neoplasia is approximately 8.25 years (99.45 months), with a range of 12 to 300 months. Soft tissue sarcoma is the most prevalent histologic diagnosis, accounting for 26.4% of all cases, followed by chromatophoromas (pigment cell tumors) and gonadal tumors.

Etiology and Pathophysiology

Causative Factors

Known and suspected factors contributing to neoplasia in fish include genetic predisposition, viral infections, environmental carcinogens, chronic inflammation, parasites, and UV radiation. Some tumors are genetically mediated, such as the malignant melanoma of the platy-swordtail cross. Retroviruses have been associated with several fish neoplasms including walleye dermal sarcoma, lymphosarcoma in northern pike, and swim bladder fibrosarcoma in Atlantic salmon.