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Multicentric orocutaneous fibrosarcoma in a fork-tailed catfish (Hemiarius dioctes).

Because of their abundance, diversity, longevity and the intimate relationship between their health and water quality, fish are important biological indicators of aquatic environmental health (Sindermann 1996; Ferguson 2006). Epidemics of neoplasia in fish have been documented in heavily polluted waters, and in some instances laboratory induction studies have later supported the role of environmental carcinogens of human health significance (Black & Baumann 1991; Bunton 1996). Thus, it is prudent to monitor for and document fish health in industrial areas, and some advocate using fish as sentinels for monitoring aquatic pollution (Sindermann 1996). In this communication, we report the clinicopathological features of multiple orocutaneous fibrosarcomas in a warrior catfish (Hemiarius dioctes) sampled from a river mouth with a catchment containing extensive mineral deposits as well as decommissioned uranium and copper mines (Lord 1956). Catfish were sampled together with several other species of finfish and crustaceans as part of a fish health monitoring programme conducted longitudinally to examine potential environmental effects of dredging for the Ichthys LNG Project in Darwin Harbour, Northern Territory, Australia (Cardno 2014). During the two years of fish health monitoring conducted both before (baseline) and every 6 months during the Project’s dredging programme, a total of 183 fork-tailed catfish (Arius spp. and Hemiarius spp.) were captured using hook and line, crab traps or gill nets and examined for external signs of disease by field sampling staff in Darwin Harbour (12°290S, 130°490E, n = 32 catfish), and two reference sites remote to the Project that were located in Bynoe Harbour (12°410S, 130°340E, n = 33 catfish) and the mouth of the Adelaide River (12°130S, 131°130E, n = 118 catfish). Of these fish, only one catfish from Darwin Harbour was considered by field staff to be abnormal due to ventral dermal redness (prevalence of abnormal catfish in Darwin Harbour = 3.1%), while six catfish from the Adelaide River reference site were considered abnormal (prevalence of abnormal fish in Adelaide River = 5.1%) (Cardno 2014). No abnormal catfish were sampled from the Bynoe Harbour site. All abnormal fish were euthanased by iki-jime before being transported on ice back to the laboratory for necropsy as part of a standardized fish health assessment programme. For occupational health and safety considerations, spines from the dorsal and pectoral fins of each catfish were cut off with pliers by field staff after euthanasia. Only one of the 183 catfish examined exhibited clinicopathological features of fibrosarcoma. The affected Hemiarius dioctes was taken on hook and line on 9 October 2012 from the reference site near the mouth of the Adelaide River. The affected fish was a juvenile in poor condition, 23.5 cm in length, weighing 168 g. Multiple (9–10) masses protruded from the skin and Correspondence B K Diggles, (e-mail: ben@digsfish.com)