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Histological assessment of organs in sexually mature and post-spawning steelhead trout and insights into iteroparity

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Abstract

Steelhead trout (Oncorhynchus mykiss) are anadromous and iteroparous, but repeat-spawning rates are generally low. Like other anadromous salmonids, steelhead trout fast during freshwater spawning migrations, but little is known about the changes that occur in vital organs and tissues. We hypothesized that fish capable of repeat-spawning would not undergo the same irreversible degeneration and cellular necrosis documented in semelparous salmon. Using Snake River steelhead trout as a model we used histological analysis to assess the cellular architecture in the pyloric stomach, ovary, liver, and spleen in sexually mature and kelt steelhead trout. We observed 38 % of emigrating kelts with food or fecal material in the gastrointestinal tract. Evidence of feeding was more likely in good condition kelts, and feeding was associated with a significant renewal of villi in the pyloric stomach. No vitellogenic oocytes were observed in sections of kelt ovaries, but perinucleolar and early/late stage cortical alveolus oocytes were present suggesting iteroparity was possible. We documented a negative correlation between the quantity of perinucleolar oocytes in ovarian tissues and fork length of kelts suggesting that larger steelhead trout may invest more into a single spawning event. Liver and spleen tissues of both mature and kelt steelhead trout had minimal cellular necroses. Our findings indicate that the physiological processes causing rapid senescence and death in semelparous salmon are not evident in steelhead trout, and recovery begins in fresh water. Future management efforts to increase iteroparity in steelhead trout and Atlantic salmon must consider the physiological processes that influence post-spawning recovery.

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Acknowledgments

Funding for this study was provided by the Columbia River Inter-Tribal Fish Commission through the Columbia Basin Fish Accords partnership with the Bonneville Power Administration under project 2007-401-00, Doug Hatch, project manager. We thank the staff at Dworshak National Fish hatchery for their cooperation with sampling. The US Army Corps of Engineers, and Nez Perce Tribe provided assistance with logistics of sampling at Lower Granite Dam juvenile fish bypass facility. We thank Dr. Rajan Bawa and staff at Colorado Histo-prep for processing tissues samples for microscopic analysis. Ann Norton, Boling Sun, James Nagler, Chris Williams, Andrew Pierce, and Victor Cajas of the University of Idaho provided invaluable assistance in interpretation of samples, laboratory and field assistance. We thank Amy Long, Vicki Blazer, Bill Ardren, and two anonymous reviewers for their suggestions and scientific critique of this manuscript. Additional sampling support was provided by Aaron Penney, Jessica Buelow, Kala Hamilton, Andrew Pape, William Schrader, Martin Perales, Veatasha Dorsey, and Bryan Jones. This study was performed under the auspices of University of Idaho protocol # 2009–2010. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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  1. Idaho Cooperative Fish and Wildlife Research Unit, Department of Fish and Wildlife Sciences, University of Idaho, Moscow, ID, USA

    Zachary L. Penney

  2. United States Geological Survey Idaho, Cooperative Fish and Wildlife Research Unit, Department of Fish and Wildlife Sciences, University of Idaho, Moscow, ID, USA

    Christine M. Moffitt

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Penney, Z.L., Moffitt, C.M. Histological assessment of organs in sexually mature and post-spawning steelhead trout and insights into iteroparity. Rev Fish Biol Fisheries 24, 781–801 (2014). https://doi.org/10.1007/s11160-013-9338-2

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