Abstract
An adult female kelp greenling (Hexagrammos decagrammus) housed in a public aquarium was presented for evaluation of a mass originating from the left lateral body wall. The fish was housed in a 90,000-gallon, multi-species, temperate marine exhibit. The fish had developed the body wall mass nine months prior; a previous biopsy yielded a diagnosis of sarcoma, which was suspected to be an osteosarcoma, and secondary ulcerative dermatitis. The fish was treated at that time with a course of antimicrobials to address the dermatitis. At a recheck exam one month after the initial biopsy, the mass appeared to be static, the ulcerative dermatitis has improved significantly, and the fish had continued to display normal feeding behavior and maintained a constant body weight.
At catch up for a routine freshwater dip for ectoparasites nine months later, the greenling was separated for recheck. The fish weighed 1.42 kg, which was consistent with the last recorded weight eight months previously. Physical exam was notable for proliferative soft tissue masses around the base of the pelvic fins and the previously-documented mass on the left lateral body wall; the mass on the body wall appeared static when compared to photographs and measurements of the previous exam. The fish was anesthetized for radiographs and biopsies. A full-thickness punch biopsy was collected from the mass on the lateral body wall and from the masses on the ventrum. Whole body radiographs showed the region of swelling on the left lateral body wall and mild medial deviation of the ribs underlying the mass. Histopathology of the mass on the lateral body wall showed areas of osteoid production associated with elongated cells with distinct cytoplasmic borders, moderate amounts of eosinophilic cytoplasm, and ovoid nuclei. The neoplastic cells extended into the surrounding soft tissues multifocally and induced varying degrees of edema and inflammation. The production of osteoid associated with neoplastic cells confirmed the earlier suspicion of osteosarcoma.1 The masses on the ventrum were diagnosed as epithelial hyperplasia with a dermal granuloma and subacute inflammation; there were fragments of scale within the granuloma. Fite’s staining of the granuloma slides were negative, making acid-fast bacteria an unlikely cause of the granuloma.
The fish was found deceased a week after work up and submitted for necropsy. On necropsy there was coelomic distention, a large volume of ascites, and necrotic, resorbing eggs. On gross and histopathology there was no evidence of metastatic disease associated with the osteosarcoma and no evidence of internal granulomas. The cause of death was attributed to the resorbing egg mass, a subsequent coelomitis and metabolic derangements.
While neoplastic disease is frequently documented in fish, both mesenchymal cell tumors and etiopathological studies of neoplasia remain rare.2 The principles of managing neoplastic disease in fish vary from traditional veterinary species, largely due to the low propensity for metastasis.3 To the authors’ knowledge this is the first case of osteosarcoma documented in a marine fish species.
Acknowledgements
The authors would like to thank the entire team from the Animal Health Department and aquarium biologists at Steinhart Aquarium for their tireless efforts to provide state-of-the-art care to all of the animals under their care.
* Presenting author
+ Student presenter
Literature Cited
1. North S, Banks T. 2009. Introduction to Small Animal Oncology. Philadelphia: Saunders, Elsevier.
2. Manera M, Biavati S. 1999. Branchial osteogenic neoplasm in barbel Barbus barbus plebejus. Dis Aquat Org. 37:231–236.
3. Vergneau-Grosset C, Nadeau ME, Groff JM. 2017. Fish oncology: diseases, diagnostics, and therapeutics. Vet Clin North Am Exot Anim Pract. 20:21–56.