DAO 88:115-126 (2010)  -  DOI: https://doi.org/10.3354/dao02150

Ruptured yolk sacs and visceral fungi in emergent pink salmon alevins: histopathology and relation to marine survival

Gary D. Marty1,3,*, Ronald A. Heintz2

1Department of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California, 1 Shields Ave., Davis, California 95616-8732, USA
2National Marine Fisheries Service, Auke Bay Laboratory, 17109 Pt. Lena Loop Rd., Juneau, Alaska 99801-8344, USA
3Present address: Animal Health Centre, Ministry of Agriculture and Lands, 1767 Angus Campbell Rd., Abbotsford, British Columbia V3G 2M3, Canada

ABSTRACT: Marine survival of anadromous salmon species is highly variable, and causes of this variability are often unknown. In the 1990s, cultured pink salmon Oncorhynchus gorbuscha alevins from 2 different regions in Alaska, USA, had years with increased postemergent mortality that could not be attributed to viruses, bacteria, or parasites. In both regions, lifetime marine survival of the most severely affected fish groups was as low as 1.1% in 1 region and 0.13% in the other region. To determine causes of morbidity, alevins from both regions were sampled for detailed histopathology (n = 144 and 36). Microscopic lesions associated with increased postemergent mortality included ruptured yolk sacs or ‘coagulated yolk’ (up to 38% of abnormal fish affected) and invasive fungi in the stomach or swimbladder (up to 39% of abnormal fish affected). The diagnosis of a ruptured yolk sac was based on the presence of yolk protein in the peritoneal cavity. Putative yolk proteins sometimes also distended peritoneal macrophages, systemic vessels, hepatocyte cytoplasm, splenic macrophages, and renal ducts. The most severe case of visceral fungi had hyphae invading from the stomach into the swimbladder and kidney. In the hatchery with the greatest postemergent mortality, 38% of the abnormal fish sampled had no significant microscopic lesions. We hypothesize that ruptured yolk sacs and visceral fungi occurred in fish that were predisposed to develop these lesions because of poor body condition. High prevalence of these lesions might be a useful marker for predicting poor marine survival.

KEY WORDS: Pink salmon · Oncorhynchus gorbuscha · Ruptured yolk sac · Alevins · Histopathology · Marine survival

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Cite this article as: Marty GD, Heintz RA (2010) Ruptured yolk sacs and visceral fungi in emergent pink salmon alevins: histopathology and relation to marine survival. Dis Aquat Org 88:115-126. https://doi.org/10.3354/dao02150

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