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Alaska Fisheries Technical Report Number 60 Morbidity of Tagged Wild Adult Fall Chum Salmon Captured by Fish Wheel in the Yukon River, Alaska April 2002 Region 7 U.S. Fish and Wildlife Service ! Department of the Interior Morbidity of Tagged Wild Adult Fall Chum Salmon Captured by Fish Wheel in the Yukon River, Alaska Alaska Fisheries Technical Report Number 60 by Kathy Burek, D. V. M.1 and Tevis J. Underwood 2 Key words: fall chum salmon, Oncorhynchus keta, mortality, Yukon River, fish wheel, tag, necropsy, pathology, histopathology, condition factors, hematology, Loma salmonae, Icthyophonus hoferi, Parvicapsula sp, parasites 1 Alaska Veterinary Pathology Services, 23834 The Clearing Drive Eagle River, Alaska 99577 2 U.S. Fish and Wildlife Service, Fairbanks Fishery Resource Office 101 12th Ave., Box 17, Room 222, Fairbanks, Alaska, 99701 April 2002 Disclaimers The mention of trade names or commercial products in this report does not constitute endorsement or recommendation for use by the Federal government. The U.S. Department of the Interior prohibits discrimination in programs on the basis of race, color, national origin, religion, sex, age, or disability. If you believe that you have been discriminated against in any program, activity, or facility operated by the U.S. Fish and Wildlife Service or if you desire further information please write to: U.S. Department of the Interior Office for Equal Opportunity 1849 C. Street, NW Washington, D. C. 20240 This research was funded by the U. S. Fish and Wildlife Service under contract number 70181-8-M491 to Dr. Kathy Burek, Alaska Veterinary Pathology Services, 23834 The Clearing Drive, Eagle River, Alaska 99577 The correct citation for this report is: Burek, K., and T. J. Underwood. 2002. Morbidity of tagged wild adult fall chum salmon captured by fish wheel in the Yukon River, Alaska. U. S. Fish and Wildlife Service, Fairbanks Fishery Resource Office, Alaska Fisheries Technical Report Number 60, Fairbanks, Alaska. ii Abstract A mark-recapture study using fish wheels and spaghetti tags was conducted annually on migrating Yukon River chum salmon since 1996. A substantial decrease in the relative abundance of tagged fish was observed with increased distance upstream, potentially indicating excessive mortality of tagged fish. To evaluate causes of mortality and morbidity and describe histologic changes during migration, chum salmon were sampled and examined by full necropsies that included external lesions, weight, length, hematology, bacteriology, ELISA for bacterial kidney disease antigen, and semiquantitative histopathology. To assess body condition, Fulton’s condition factor, hepatosomatic and gonadosomatic, indices, were determined. None of these analyses indicated a definitive cause for mortality or morbidity specific to the tagged fish. Local damage at the tag site, higher neutrophil numbers, and lower total protein in tagged fish suggested further study into the possibility of infection as a cause of mortality associated with tagging. A single untagged fish had a systemic infection of Aeromonas salmonicida. These bacteriology results indicated that septicemia from tagging was not occurring during the interval examined. There was one weak positive for an antigen of the bacterial kidney disease agent indicating that this disease was not a significant factor in morbidity. Blood smears were negative for viral erythrocytic necrosis inclusion bodies. Lesions suggestive of other major infectious diseases were not evident. Lesions typical of these migrating salmon included somatic and gastrointestinal skeletal muscle degeneration, contraction band necrosis in the heart, fibrin thrombi in the heart and gills, apoptosis of the gastrointestinal epithelial cells, bone remodeling, ulcers, vacuolar change in the islets of Langerhans and zymogen granule depletion in the pancreas, and mesenteric fat atrophy. Parasites included Ichthyophonus hoferi, Loma salmonae in the gill and intra- arterial, an unidentified microsporidian in the kidney, a myxosporidian Parvicapsula sp. in the kidney and intestine, nematode larvae within the walls of the stomach and intestine, intestinal cestodes, and gastric trematodes. iii Table of Contents Abstract ................................................................. iii Table of Contents.......................................................... iv List of Tables..............................................................v List of Figures ............................................................ vi Introduction ...............................................................1 Study Area ................................................................1 Methods ..................................................................2 Capture Techniques...................................................2 Field and Laboratory Processing.........................................2 Data Analysis........................................................3 Results...................................................................4 Necropsy Findings....................................................4 Tag Site Gross and Histologic Features....................................5 Bacteriology ........................................................5 Bacterial Kidney Disease (BKD) ELISA ..................................5 Hematology.........................................................6 Histopathology ......................................................6 Discussion and Conclusions .................................................12 Acknowledgments .........................................................19 References ...............................................................20 iv List of Tables Table Page Table 1.— Grading systems of histologic lesions. ...............................23 Table 2.— External lesion scores. ...........................................30 Table 3.— Morphometrics results. ...........................................31 Table 4.— Hematology results. ..............................................32 Table 5.— Heart lesion results. ..............................................35 Table 6.— Liver lesion results. ...............................................37 Table 7.— Musculoskeletal system and subcutaneous tissue lesion results. ...........38 Table 8.— Spleen lesion results. .............................................39 Table 9.— Gill lesion results. ...............................................40 Table 10.— Gastrointestinal lesion results. .....................................41 Table 11.— Kidney lesion results. ............................................42 Table 12.— Pancreatic lesion results. ..........................................44 Table 13.— Parasite grading results. .........................................45 Table 14.— Ichthyophonus infected fish and organs affected in each (+ means present and - means absent). ......................................................47 v List of Figures Figure Page Figure 1.– Usual gross appearance of the tag site. ................................48 Figure 2.– Tag site with an ulcer at the base of the caudal aspect of the dorsal fin. ......48 Figure 3a.– Typical histologic appearance of the tag site. The continuity of the epithelium was disrupted and the tag tract was filled with necrotic debris, neutrophils and occasionally refractile material consistent with scale fragments. ............... 49 Figure 3b.– Irregularly shaped refractile material (large arrow) and necrotic debris present within the tag tract. ..................................................49 Figure 4.– Ulcer and SQ bacterial colonies from a fish with A. salmonicida cultured from the kidney (bar in insert = 20:m)...........................................49 Figure 5.– Zenker’s necrosis in the heart characterized by hypereosinophilia, and presence of dark transversely placed contraction bands. ............................49 Figure 6.– Fibrin thrombi and endocarditis. ....................................50 Figure 7.– Lymphocyte aggregates in the heart and mixed inflammatory cells in the epicardium. In the overview, there is a small aggregate of lymphocytes within the myocardium (arrow) and a sprinkling of mixed inflammatory cells within the epicardium..........................................................50 Figure 8.– Myocyte vacuolation. .............................................50 Figure 9.– A degenerated Ichthyophonus hoferi resting spore within the epicardium. It is surrounded by and infiltrated by neutrophils, macrophages and multinucleated giant cells. .............................................................50 Figure 10.– Typical features of the hepatocytes in the females (left side) versus the males (right side). ......................................................51 Figure 11.– Fibrin thrombi and apoptotic cells (arrow) in the secondary lamella ofthe gill. ..................................................................51 Figure 12a.– Microsporidia xenoma in gill tissue. ..................................................................51 vi Figure 12b.– Microsporidia xenoma in gill tissue with an immunohistochemical positive reaction to monoclonal antibody for Loma salmonae. .......................51 Figure 13a.– Intravascular Loma salmonae xenoma in the primary lamella (arrowhead) with a thrombus and vasculitis in the distal blood vessel (arrow). ..................52 Figure 13b.– Higher power view of the thrombus and associated neutrophilic vasculitis. 52 Figure 14.– Apoptosis of epithelial cells

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