Intestinal lesions and parasites associated with senescence and prespawn mortality in Chinook Salmon (<i>Oncorhynchus tshawytscha</i>)

Nervino, Stephanie; Polley, Tamsen; Peterson, James T.; Schreck, Carl B.; Kent, Michael L.; Alexander, Julie D.

doi:10.1111/jfd.13876

Cited by 5 publications

References 80 publications

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Influence of stream temperature and human disturbance on prespawn mortality of Chinook Salmon in the Willamette River basin

Carey,

Kent,

Schreck

et al. 2024

N American J Fish Manag

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ObjectivePremature mortality of adult female Chinook Salmon Oncorhynchus tshawytscha is a major barrier to population recovery. The Willamette River basin, Oregon, typifies the problems that are faced by fishery managers in the Pacific Northwest (USA). Adult salmon are trapped and transported upstream of dams to access historical spawning grounds, but annual rates of prespawn mortality (PSM) are high (often >40%) and may limit the recovery of natural populations. The purpose of this study was to identify potential factors related to PSM of female Chinook Salmon that are outplanted above dams and incorporate them into a modeling framework to facilitate adaptive management of outplanting operations.MethodsWe evaluated PSM in Fall Creek of the Willamette River basin prior to transport facility improvements in summer and fall of 2010–2017 and postimprovement during 2020–2021. We estimated PSM and conducted exploratory analyses to identify possible nontransport sources of stress that may contribute to the observed high PSM rates. Candidate factors included long‐term elevated temperature exposure, elevated temperature exposure below the trap, total number of outplanted fish, and monthly human disturbance of outplanted fish. We then developed and fit three models, each representing a hypothesis of a factor influencing PSM, incorporated them into a single alternative decision model, and conducted sensitivity analyses.ResultPrespawn mortality averaged 0.66 (ranging from 0.37 to 0.94) over the study period. According to the simulation results, the top two management actions were to exclude human activities—swimming and fishing—from Fall Creek in July and August.ConclusionExpected PSM rates were predicted to be 0.38 when human activity was excluded in July and 0.37 for August. Sensitivity analyses indicated that the most influential decision model component was the choice of the alternative model.

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Influence of stream temperature and human disturbance on prespawn mortality of Chinook Salmon in the Willamette River basin

Carey,

Kent,

Schreck

et al. 2024

N American J Fish Manag

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Gut microbiome composition associates with corticosteroid treatment, morbidity, and senescence in Chinook salmon (Oncorhynchus tshawytscha)

Couch

Neal

Herron

et al. 2023

Sci Rep

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Pacific salmon experience prolonged elevation in corticosteroid hormones during important life history events including migration, reproduction, and senescence. These periods of elevated corticosteroids correspond with changes to immunity and energy metabolism; therefore, fish may be particularly vulnerable to mortality at these times. Recent studies found that stress-induced cortisol release associated with microbial community shifts in salmonids, raising the question of how longer-term corticosteroid dynamics that accompany life history transitions affect salmonid microbiomes. In this work, we experimentally evaluated the relationships between gut microbiome composition, chronically elevated corticosteroids, and mortality in juvenile Chinook salmon (Oncorhynchus tshawytscha). We found that treatment with slow-release implants of the corticosteroids cortisol or dexamethasone resulted in changes to the gut microbiome. Morbidity was also associated with microbiome composition, suggesting that the gut microbiome reflects individual differences in susceptibility to opportunistic pathogens. Additionally, we analyzed a small number of samples from adult fish at various stages of senescence. Results from these samples suggest that microbiome composition associated with gut integrity, and that the microbial communities of corticosteroid treated juveniles shift in composition toward those of senescent adults. Overall, findings from this work indicate that the gut microbiome correlates with mortality risk during periods of chronic corticosteroid elevation.

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A niche-adapted brain microbiome in salmonids at homeostasis

Mani,

Henn,

Couch

et al. 2023

Preprint

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Ectotherms have long been known to have peculiar relationships with microorganisms. For instance, bacteria can be recovered from blood and internal organs of healthy teleost fish. However, until now, the presence of a microbial community in the healthy teleost brain has not been proposed. Here we report a living bacterial community in the brain of healthy salmonids. Brain bacterial loads in salmonids are comparable to those found in the spleen and 1000-fold lower than in the gut. Brain bacterial communities share >50% of their diversity with gut and blood bacterial communities. Using culturomics, we obtained 54 bacterial isolates from the brain of healthy rainbow trout. Comparative genomics uncovered unique niche adaptations associated with brain colonization and polyamine biosynthesis. In a natural system, salmonid brain microbiomes shift with the host life cycle, becoming dysbiotic in reproductively mature Chinook salmon, a species that undergoes reproductive death. Our study redefines the relationship between the teleost brain and bacterial microbiomes under physiological conditions. We posit that this symbiosis may endow salmonids with a direct mechanism to sense and respond to environmental microbes.One-Sentence SummarySalmonids have a brain-adapted, resident bacterial community

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Intestinal lesions and parasites associated with senescence and prespawn mortality in Chinook Salmon (Oncorhynchus tshawytscha)

Cited by 5 publications

References 80 publications

Influence of stream temperature and human disturbance on prespawn mortality of Chinook Salmon in the Willamette River basin

Influence of stream temperature and human disturbance on prespawn mortality of Chinook Salmon in the Willamette River basin

Gut microbiome composition associates with corticosteroid treatment, morbidity, and senescence in Chinook salmon (Oncorhynchus tshawytscha)

A niche-adapted brain microbiome in salmonids at homeostasis

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