• First described by Duncan (1978) and McKnight (1978) in Scotland.
• Tumor was described as leiomyosarcoma of the swimbladder
• Tumors were associated with oncovirus (Duncan 1978)
• Twenty years later swim bladder tumors were detected in wild salmon originating from the Pleasant River in Maine which were raised in a hatchery in Attleboro, Massachusetts. These fish were received 1996 as 2+ and 1+ age. Tumors were first seen in November 1997 in 3+ age group. Mortality continued into 1998 with most morts having swim bladder tumors.
• September 1998 retrovirus was detected in tumors by Cornell researchers (J.Casey, P. Bowser).
• Pleasant River stock was also kept in a hatchery in Maine isolated from commercial stock as part of a river specific restocking plan. These fish were immature 2+ age, with some precocious males.
• November 1998 36 blood samples were taken and tested by J.Casey, Cornell, by PCR for retrovirus. 2 fish tested positive. None of the fish exhibited any clinical signs. The fish ranged from 75 grams to 450 grams+ in weight.
• December 1998 all 76 Pleasant River fish in the Maine hatchery were euthanized. The fish were examined grossly for tumors externally and internally. No tumors were detected.
• June 1998, a large tumor associated with the kidney was seen at a processing plant in a market fish. This tumor was associated with the kidney and not with the swim bladder. The tumor was determined to be a neural tumor by Hugh Ferguson (Sterling, Scotland) and John Harshbarger (George Washington University) and named a neurofibroma and ganglioneuroma respectively. P. Bowser, Cornell, confirmed that the tumor was different from the swimbladder tumor.
• An interview of the HACCP trained supervisor and quality control person at the processing plant revealed that swim bladder tumors have never been seen at the processing line in the 3+YC or any other YC.
• Annually more than 3000 brood stock have been inspected and routinely tested by AFS certified fish health inspectors (Micro Technologies, Inc). No swim bladder tumor has ever been seen in commercial broodstock in Maine.
• There is no evidence of swim bladder tumors in commercial salmon in Maine at this time.
• The source of the retrovirus in the Pleasant River stock remains unknown.

References:

Duncan, I.B. 1978. Evidence for an oncovirus in swim bladder fibrosarcoma of Atlantic salmon Salmo salar L. J. Fish Dis. 1:127-131.

McKnight, I.J. 1978. Sarcoma of the swim bladder of Atlantic salmon (Salmo salar L.). Aquaculture 13:55-60.

K. Wolf. Fish viruses and fish viral diseases. Atlantic Swimbladder sarcoma virus. Pg.349-351. Comstock Publishing Associates. Ithaca and London.

Bruno D.V. and T.T. Poppe. 1996. A color Atlas of Salmonid Diseases. Tumours: Sarcoma of the swim bladder. 109-110.

For more information on this topic contact mopitz@umext.maine.edu