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Objective: Premature 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. Methods: We 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. Result: Prespawn 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. Conclusion: Expected 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. Impact StatementAlthough trap and haul operations allow wild salmon populations to access historical spawning grounds, despite impoundment structures, populations are hindered by high prespawn mortality rates and recovery efforts may benefit from an adaptive management plan. [ABSTRACT FROM AUTHOR]

Prespawn mortality (PSM) presents a major problem for the recovery of spring Chinook Salmon (Oncorhynchus tshawytscha) populations. In the Willamette River, Oregon, PSM exceeds 90% in some years but factors explaining it are not well understood. We examined intestinal tissue samples using histological slides from over 783 spring Chinook Salmon collected between 2009 and 2021, which included tissues from PSM fish, artificially spawned captive broodstock (BS) and normal river run fish, comprised of trapped (Live) and naturally post‐spawned river (RPS) fish collected from the river. We observed degeneration of the intestinal epithelium and loss of villous structure, with concurrent severe enteritis. A natural progression of decline in epithelial integrity (EI) through the summer and fall until spawning and subsequent death was also observed. Live fish exhibited high EI scores (mean = 68%), BS exhibited variable EI scores (35%) and RPS exhibited severe loss of EI (14%). PSM fish exhibited prominent loss of intestinal epithelium with EI scores (13%), very similar to RPS fish, despite having been collected earlier in the year. Hence, we argue that low EI scores are strongly linked with PSM. Ceratonova shasta and Enterocytozoon schreckii were common in all groups, but neither were linked to either PSM or a decline in EI. [ABSTRACT FROM AUTHOR]

Here, we provide evidence that the freshwater parasitic copepod, Salmincola californiensis, acts as a vector for Aeromonas salmonicida. While investigating the effects of S. californiensis on Chinoook salmon (Oncorhynchus tshawytscha), we tangentially observed that fish infected with the copepod developed furunculosis, caused by A. salmonicida. This occurred despite being reared in pathogen‐free well water in a research facility with no prior history of spontaneous infection. We further investigated the possibility of S. californiensis to serve as a vector for the bacterium via detection of fluorescently labelled A. salmonicida inside the egg sacs from copepods in which the fish hosts were experimentally infected with GFP‐A449 A. salmonicida. We then evaluated copepod egg sacs that were collected from adult Chinook salmon from a freshwater hatchery with A. salmonicida infections confirmed by either culture or PCR. The bacterium was cultured on tryptic soy agar plates from 75% of the egg sacs, and 61% were positive by PCR. These three separate experiments indicate an alternative tactic of transmission in addition to direct transmission of A. salmonicida in captivity. The copepod may play an important role in transmission of the bacterium when fish are more dispersed, such as in the wild. [ABSTRACT FROM AUTHOR]

Structured decision making allows reintroduction decisions to be made despite uncertainty by linking reintroduction goals with alternative management actions through predictive models of ecological processes. We developed a decision model to evaluate the trade-offs between six bull trout (Salvelinus confluentus) reintroduction decisions with the goal of maximizing the number of adults in the recipient population without reducing the donor population to an unacceptable level. Sensitivity analyses suggested that the decision identity and outcome were most influenced by survival parameters that result in increased adult abundance in the recipient population, increased juvenile survival in the donor and recipient populations, adult fecundity rates, and sex ratio. The decision was least sensitive to survival parameters associated with the captive-reared population, the effect of naivety on released individuals, and juvenile carrying capacity of the reintroduced population. The model and sensitivity analyses can serve as the foundation for formal adaptive management and improved effectiveness, efficiency, and transparency of bull trout reintroduction decisions. Le processus decisionnel structure permet la prise de decisions de reintroduction meme en presence d'incertitude, en reliant les objectifs de reintroduction a differentes mesures de gestion par l'entremise de modeles de prevision de processus ecologiques. Nous avons mis au point un modele decisionnel pour evaluer les compromis entre six decisions de reintroduction d'ombles a tete plate (Salvelinus confluentus) dans le but de maximiser le nombre d'adultes dans la population receptrice sans reduire la population donatrice a un niveau inacceptable. Des analyses de sensibilite portent a croire que des parametres associes a la survie qui se traduisent par une abondance d'adultes accrue dans la population receptrice, une survie accrue des juveniles dans les populations donatrice et receptrice et les taux de fecondite et les rapports de masculinite des adultes exercent la plus grande influence sur l'identite et les resultats de la decision. La decision etait moins sensible a des parametres de survie associes a la population elevee en captivite, a l'effet de la naivete sur les individus relaches et a la capacite de charge de juveniles de la population reintroduite. Le modele et les analyses de sensibilite peuvent servir de base pour une gestion adaptative formelle et pour ameliorer l'efficacite, l'efficience et la transparence des decisions concernant la reintroduction d'ombles a tete plate. [Traduit par la Redaction], Introduction Bull trout (Salvelinus confluentus) require cold water for spawning and early rearing (Buchanan and Gregory 1997), and if climate change predictions are accurate and habitat degradation and fragmentation continue [...]

Lampreys (Petromyzontiformes) have persisted over millennia and now suffer a recent decline in abundance. Complex life histories may have factored in their persistence; anthropogenic perturbations in their demise. The complexity of life histories of lampreys is not understood, particularly for the anadromous Pacific lamprey, Entosphenus tridentatus Gairdner, 1836. Our goals were to describe the maturation timing and associated characteristics of adult Pacific lamprey, and to test the null hypothesis that different life histories do not exist. Females exhibited early vitellogenesis--early maturation stages; males exhibited spermatogonia--spermatozoa. Cluster analyses revealed an 'immature' group and a 'maturing-mature' group for each sex. We found statistically significant differences between these groups in the relationships between (i) body mass and total length in males; (ii) Fulton's condition factor and liver lipids in males; (iii) the gonadosomatic index (GSI) and liver lipids in females; (iv) GSI and total length in females; (v) mean oocyte diameter and liver lipids; and (vi) mean oocyte diameter and GSI. We found no significant difference between the groups in the relationship of muscle lipids and body mass. Our analyses support rejection of the hypothesis of a single life history. We found evidence for an 'ocean-maturing' life history that would likely spawn within several weeks of entering fresh water, in addition to the formerly recognized life history of spending 1 year in fresh water prior to spawning--the 'stream-maturing' life history. Late maturity, semelparity, and high fecundity suggest that Pacific lamprey capitalize on infrequent opportunities for reproduction in highly variable environments. Key words: primitive, Petromyzontiformes, life history. Si les lamproies (petromyzontiformes) persistent depuis des millenaires, leur abondance est, depuis peu, a la baisse. Des cycles biologiques complexes pourraient en partie expliquer leur persistance, et des facteurs anthropiques, leur declin. La complexite des cycles biologiques des lamproies est mal comprise, particulierement en ce qui concerne la lamproie du Pacifique, Entosphenus tridentatus Gairdner, 1836, une espece anadrome. Nos objectifs consistaient a decrire le moment des differents stades de maturation des lamproies du Pacifique adultes et les caracteristiques connexes, et a tester l'hypothese nulle selon laquelle il n'y a pas differents cycles biologiques. Les femelles presentaient des stades de vitellogenese precoce et de maturation precoce; les males, les stades de spermatogonie et spermatozoide. Des analyses typologiques ont revele un groupe << immature >> et un groupe << en cours de maturation-mature >> pour chacun des sexes. Nous avons releve des differences statistiquement significatives entre ces groupes dans les relations entre (i) la masse corporelle et la longueur totale chez les males, (ii) l'indice d'embonpoint de Fulton et les lipides hepatiques chez les males, (iii) l'indice gonadosomatique (GSI) et les lipides hepatiques chez les femelles, (iv) le GSI et la longueur totale chez les femelles, (v) le diametre moyen des oocytes et les lipides hepatiques et (vi)le diametre moyen des oocytes et le GSI. Nous n'avons decele aucune difference significative entre les groupes en ce qui concerne le lien entre les lipides musculaires et la masse corporelle. Nos analyses appuient le rejet de l'hypothese d'un cycle biologique unique. Nos observations appuient l'existence d'un cycle biologique de << maturation oceanique >> dans lequel le frai a probablement lieu quelques semaines apres l'entree en eau douce, en plus du cycle biologique deja connu comprenant une annee en eau douce prealablement au frai, soit le cycle biologique de << maturation en riviere >>. La maturite tardive, la semelparite et la grande fecondite de la lamproie du Pacifique donnent a penser que ce poisson mise sur des occasions de reproduction peu frequentes dans des milieux tres variables. [Traduit par la Redaction] Mots-cles: primitif, petromyzontiformes, cycle biologique., Introduction Lampreys (Petromyzontiformes) have changed very little since they appeared in the fossil record over ~300 to 500 million years ago (Dawkins 2004; Janvier 2008; Helfman et al. 2009). Despite [...]

We report the incidence of male intersex in adult Pacific lamprey (Entosphenus tridentatus (Richardson, 1836)) during their pre-spawning migration in fresh water. Although 'hermaphrodites' have been suggested in other adult lampreys, this is the first detailed description and discussion of this phenomenon. A total of 0.5% of our adult Pacific lamprey from Willamette Falls (2 out of 427 adults) were intersex, with oocytes in the testes. This phenomenon was identifiable only by histological examination. The testes of the intersex males were immature, in the beginning stages of meiosis. One intersex male possessed primary growth or perinucleolar stage oocytes loosely interspersed throughout the testes, and the other possessed at least 6 mid-vitellogenic oocytes (0.6 mm, mean long diameter) separate from the testes. Because premetamorphic lamprey can possess both female and male gonial cells, we hypothesize that intersex is a remnant larval trait and that these fish failed to fully develop into males during metamorphosis. Key words: intersex, gonochoristic, primitive fish, reproduction, maturation, cyclostomes. Nous rendons compte de l'incidence d'intersexualite chez des males adultes de lamproie du Pacifique (Entosphenus tridentatus (Richardson, 1836)) durant leur migration en eau douce precedant le frai. Bien que la presence << d'hermaphrodites >> ait ete suggeree chez d'autres lamproies adultes, il s'agit des premieres description et discussion detaillees de ce phenomene. Au total, 0,5 % des lamproies du Pacifique adultes de Willamette Falls recensees (2 individus sur 427 adultes) etaient intersexuelles, presentant des oocytes dans les testicules. Ce phenomene n'est observable que par un examen histologique. Les testicules des males intersexuels etaient immatures, aux stades initiaux de la meiose. Un male intersexuel possedait des oocytes au stade de croissance primaire ou perinucleolaire dissemines ca et la dans les testicules et l'autre possedait au moins six oocytes a des stades intermediaires de la vitellogenese (diametre long moyen de 0,6 mm) separes des testicules. Etant donne que la lamproie premetamorphique peut presenter des cellules goniales femelles et males, nous avons emis l'hypothese que l'intersexualite est un caractere larvaire residuel et que ces poissons ne se sont pas developpes completement en individus males durant la metamorphose. Mots-cles : intersexualite, gonochoriste, poisson primitif, reproduction, maturation, cyclostomes. [Traduit par la Redaction], Introduction Hermaphroditism, either sequential or synchronous, exists in approximately 5% to 6% of all animal species (Grober and Rodgers 2007) and approximately 2% of all extant teleost fishes, across 20 [...]

Abstract: Expression of distinct corticosteroid receptor genes, glucocorticoid receptors 1 and 2 (GR-1 and GR-2, respectively) and mineralcorticoid receptor (MR), was quantified by real-time polymerase chain reaction (PCR) in peripheral [...]

We evaluated the effect of short-term exposures to a xenobiotic chemical during early life-history stages on the long-term immune competence of chinook salmon (Oncoryhnchus tshawytscha). Immersion of chinook salmon eggs [...]