Mortality Of Trout Research Articles

Habitat segregation by sympatric juvenile Arctic charr and brown trout in shallow lake areas: a consequence of interspecific differences in predator avoidance?

In sympatry, juvenile brown trout (Salmo trutta) usually occupy the shallow and most productive areas (littoral zone) of lakes, while juveniles of Arctic charr (Salvelinus alpinus) are found in deeper, less productive parts. In contrast, when Arctic charr juveniles occur in allopatry, they often occupy shallow littoral areas as well. Habitat segregation has traditionally been interpreted as a trade-off between predation risk and energy gain, while the segregation of these two species has been explained by brown trout being more aggressive and competitively superior to Arctic charr. We hypothesize, however, that the marked habitat segregation between the two species may also be due to differences in predator avoidance. Accordingly, we conducted several laboratory tests, using Arctic charr and brown trout as potential predators. Live fish of the same species were offered as prey, either as small charr only, small trout only, or both small charr and small trout together. Artificial shelters were then introduced to examine the avoidance ability of prey fish against predatory fish. Our results showed that under these circumstances, access to shelters strongly decreased mortality in juvenile brown trout, but had no effect on juvenile Arctic charr mortality. Thus, the habitat segregation shown by sympatric juvenile Arctic charr and brown trout in lakes may be a consequence of interspecific differences in predator avoidance.

Glyphosate- and aminomethylphosphonic acid (AMPA)-induced mortality and residues in juvenile brown trout (Salmo trutta f. fario) exposed at different temperatures

BackgroundGlyphosate is a broad-spectrum, non-selective systemic herbicide with a commonly assumed low potential for accumulation in biota. Nevertheless, glyphosate has been shown to bioaccumulate in the tissues of several organisms. To understand the bioconcentration dynamics of glyphosate in fish, brown trout (Salmo trutta forma fario) of different age were exposed to different concentrations of glyphosate, the formulation Roundup® LB Plus, and the major transformation product aminomethylphosphonic acid (AMPA) for two, three, or four weeks at different temperatures in the laboratory. Mortality rates were determined, and tissue samples were collected at the end of the experiment to ascertain concentrations of glyphosate and AMPA residues by liquid chromatography coupled to mass spectrometry (LC–MS/MS).ResultsBrown trout mortality during exposure to glyphosate or AMPA was considerably higher at 15 °C than at 7 °C. Also, a significant increase in glyphosate concentrations in samples containing muscle, head, backbone, and caudal fin tissue with increasing exposure concentrations and temperatures was observed. Six-month-old fish contained more glyphosate per kg wet weight after exposure than ten-month-old fish. The bioconcentration factors (BCFs) for glyphosate and AMPA were much higher at 15 °C than at 7 °C, but in both cases decreased with higher glyphosate concentrations. The BCF for glyphosate formulated in Roundup® was higher than the one for the parent compound. Approximately 30–42% of the organ-absorbed glyphosate and AMPA remained in the tissues even when the fish were kept in clean water lacking the test substances for three weeks after termination of exposure.ConclusionOur study demonstrated that there is an interaction between glyphosate and ambient temperature in terms of toxicity. Further it was shown that increasing concentrations of glyphosate and AMPA in the surrounding media lead to significantly increased concentrations of these substances in brown trout tissues, although neither bioconcentration nor bioaccumulation of glyphosate in animal tissues is expected due to the high water solubility of this chemical. As a consequence, the uptake of glyphosate by humans through the consumption of contaminated edible fish is very likely.

Testing the Aquatic Toxicity of 2D Few-Layer Graphene Inks Using Rainbow Trout (Oncorhynchus mykiss): In Vivo and In Vitro Approaches to Support an SSbD Assessment.

Graphene-based conductive inks offer attractive possibilities in many printing technology applications. Often, these inks contain a mixture of compounds, such as solvents and stabilizers. For the safe(r) and sustainable use of such materials in products, potentially hazardous components must be identified and considered in the design stage. In this study, the hazards of few-layer graphene (FLG)-based ink formulations were tested in fish using in vitro (RTL-W1 cell line) and in vivo aquatic ecotoxicity tests (OECD TG 203). Five ink formulations were produced using different processing steps, containing varying amounts of solvents and stabilizers, with the end products formulated either in aqueous solutions or in powder form. The FLG ink formulations with the highest contents of the stabilizer sodium deoxycholate showed greater in vitro cytotoxic effects, but they did not provoke mortality in juvenile rainbow trout. However, exposure led to increased activities of the cytochrome P450 1a (Cyp1a) and Cyp3a enzymes in the liver, which play an essential role in the detoxification of xenobiotics, suggesting that any effects will be enhanced by the presence of the stabilizers. These results highlight the importance of an SSbD approach together with the use of appropriate testing tools and strategies. By incorporating additional processing steps to remove identified cytotoxic residual solvents and stabilizers, the hazard profile of the FLG inks improved, demonstrating that, by following the principles of the European Commission's safe(r) and sustainable by design (SSbD) framework, one can contribute to the safe(r) and sustainable use of functional and advanced 2D materials in products.

Neurological impairment is crucial for tire rubber-derived contaminant 6PPDQ-induced acute toxicity to rainbow trout

N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPDQ) has attracted significant attention due to its highly acute lethality to sensitive salmonids. However, studies investigating the mechanisms underlying its acute toxicity have been lacking. In this work, we demonstrated the sensitivity of rainbow trout to 6PPDQ-induced mortality. Moribund trout exhibited significantly higher brain concentrations of 6PPDQ compared to surviving trout. In an in vitro model using human brain microvascular endothelial cells, 6PPDQ can penetrate the blood–brain barrier and enhance blood–brain barrier permeability without compromising cell viability. The time spent in the top of the tank increased with rising 6PPDQ concentrations, as indicated by locomotion behavior tests. Furthermore, 6PPDQ influenced neurotransmitter levels and mRNA expression of neurotransmission-related genes in the brain and exhibited strong binding affinity to target neurotransmission-related proteins using computational simulations. The integrated biomarker response value associated with neurotoxicity showed a positive linear correlation with trout mortality. These findings significantly contribute to filling the knowledge gap between neurological impairments and apical outcomes, including behavioral effects and mortality, induced by 6PPDQ.

Characterization and pathogenicity analysis of a newly isolated strain of infectious hematopoietic necrosis virus

Rainbow trout is one of the fastest-growing aquaculture species and infectious hematopoietic necrosis virus (IHNV) is endemic throughout almost all rainbow trout farms in China nowadays. In this study, IHNV GS21 was identified as the causative pathogen, which resulted in massive mortality of rainbow trout occurring in northwest China. GS21 isolate was propagated in Chinook salmon embryonic cell line (CHSE-214) and induced apparent cytopathic effects (CPE) at 3 days post-infection (dpi). Phylogenetic analysis revealed that GS21 isolate was clustered with other reported Chinese isolates within the J genogroup. Moreover, the complete cDNA sequence of GS21 isolate was obtained and it possesses more than 98 % of ANI values and 89 % of DDH values with other Chinese IHNV isolates. The detailed sequence analysis of G gene revealed the distinct amino acid substitutions of G230, G252, G270, and I277 in GS21 isolate. Furthermore, the artificially infected rainbow trout exhibited similar clinical disease symptoms as natural infection did. The cumulative mortality infected by GS21 isolate of 104 PFU/mL reached 93 % at approximately 13.5 °C. Additionally, viral loads in tissues increased first and declined then as well as the expression of immune-associated genes. Collectively, our results characterized a novel IHNV GS21 isolate that can lead to massive mortality in juvenile rainbow trout and provided a basis to define the pathogenic characteristics and evolutionary relationship of IHNV and host immune response against IHNV infection.

Occurrence and Fate of Substituted p-Phenylenediamine-Derived Quinones in Hong Kong Wastewater Treatment Plants.

para-Phenylenediamine quinones (PPD-Qs) are a newly discovered class of transformation products derived from para-phenylenediamine (PPD) antioxidants. These compounds are prevalent in runoff, roadside soil, and particulate matter. One compound among these, N-1,3-dimethylbutyl-n'-phenyl-p-phenylenediamine quinone (6PPD-Q), was found to induce acute mortality of coho salmon, rainbow trout, and brook trout, with the median lethal concentrations even lower than its appearance in the surface and receiving water system. However, there was limited knowledge about the occurrence and fate of these emerging environmental contaminants in wastewater treatment plants (WWTPs), which is crucial for effective pollutant removal via municipal wastewater networks. In the current study, we performed a comprehensive investigation of a suite of PPD-Qs along with their parent compounds across the influent, effluent, and biosolids during each processing unit in four typical WWTPs in Hong Kong. The total concentrations of PPDs and PPD-Qs in the influent were determined to be 2.7-90 and 14-830 ng/L. In the effluent, their concentrations decreased to 0.59-40 and 2.8-140 ng/L, respectively. The median removal efficiency for PPD-Qs varied between 53.0 and 91.0% across the WWTPs, indicating that a considerable proportion of these contaminants may not be fully eliminated through the current processing technology. Mass flow analyses revealed that relatively higher levels of PPD-Qs were retained in the sewage sludge (20.0%) rather than in the wastewater (16.9%). In comparison to PPDs, PPD-Qs with higher half-lives exhibited higher release levels via effluent wastewater, which raises particular concerns about their environmental consequences to aquatic ecosystems.

No evidence of sustained recovery of native trout in response to angling suppression of invasive Brook Trout

AbstractObjectiveNonnative fish invasions have had widespread impacts on freshwater ecosystems, including effects on native fish biodiversity and persistence. Brook Trout Salvelinus fontinalis were first introduced into the Elbow River watershed (Alberta, Canada) in the 1940s. They have since become established in Quirk Creek, and they dominated the fish community by the mid‐1990s, raising concern about the native populations of Westslope Cutthroat Trout Oncorhynchus clarkii lewisi and Bull Trout S. confluentus.MethodsA targeted angling program was operated from 1998 to 2015, along with limited electrofishing removals, to suppress the Brook Trout population. We used 25 years of fish monitoring data from 1978 to 2020 to evaluate the program's effectiveness for reducing the Brook Trout population and the program's consequences for native trout.ResultDensities of Brook Trout larger than 150 mm declined after the onset of the suppression project, and the decline was attributed to removals through angling. However, Brook Trout recruitment remained comparable to presuppression levels. Westslope Cutthroat Trout recruitment increased during and after Brook Trout suppression. Densities of Westslope Cutthroat Trout larger than 150 mm increased during the suppression period but did not reach density goals targeted for recovery of the species. Bull Trout remained at very low densities throughout the suppression project.ConclusionThe lack of native trout recovery during the suppression project was hypothesized to result from (1) incidental release mortality of native trout, (2) Brook Trout suppression that was insufficient to prompt an effective response in native trout populations, or (3) a combination of these factors. Continued low densities of Brook Trout larger than 150 mm and native trout after the end of the suppression project (when harvest and incidental release mortality were alleviated) may point to some other factor impacting the recovery of trout larger than 150 mm, particularly Westslope Cutthroat Trout, since recruitment was at its highest during this period. Overall, angling was not considered an effective method for promoting native trout recovery, and other techniques should be pursued depending on management goals.

Study of in vitro reproduction of infectious pancreatic necrosis virus (IPNV)

The aim of the work was to study the in vitro reproduction of new emergent isolates of infectious pancreatic necrosis virus (IPNV) in purpose to determine virulence properties. The new strains of IPNV isolated from trout farms in Ukraine during 2021-2022 were investigated. For this purpose, RTG-2 cell line was used, on which the infectious titer of the virus and the manifestation of CPE signs were determined. The infectious titer of selected isolates in RTG-2 cell line ranged from 1.1x103 to 1.0x107 TCID50/ml Isolated IPNV strains caused low (≤25 %), moderate (≤50 %) and high (≥70 %) mortality rates in trout fry. Based on biological properties and indicators of infectious titer, the investigated isolates VN11, VN18 and VN29 were determined as with low virulence, and isolates VN20, VN30, VN32 and VN39 were classified as highly virulent. Among the highly virulent isolates, VN32 had the highest titer of 1.0x107 TCID50/ml and caused mortality in rainbow trout with an average weight of 100 g. The IPNV strain isolated from the brook trout had an infectious titer of 1.58x106 TCID50/ml and caused fry mortality ranged from 15 to 25 %. The number of detected isolates and their cultural properties testify to the biodiversity of strains for the Infectious pancreatic necrosis virus in Ukraine. How many newly discovered isolates of the IPNV belong to one or another genotype remains to be determined. For this, a study of the nucleotide sequence of the gene encoding the capsid protein VP2 will be conducted, on the basis of which it will also be possible to determine virulence by changes in amino acids sequences

Estimates of adult Lake Trout mortality fromcoded wiretags in a population with developing natural reproduction in southern Lake Michigan

AbstractObjectiveOverfishing and Sea LampreyPetromyzon marinuspredation led to extirpation of Lake TroutSalvelinus namaycushfrom Lake Michigan in the 1950s. Large populations of hatchery‐reared fish were developed by the 1970s, but natural reproduction was limited until the early 2000s when it began to increase in the southern main basin. Hypothesizing that the relatively low mortality of spawning‐aged fish contributed to this reproductive success, we estimated the total annual mortality rate for this population.MethodsWe used catch curves to estimate the total instantaneous mortality rateZusing coded wire tags, which provided definitive ages. We made separate estimates from fish collected in three on‐going surveys: a spring gill‐net survey, a fall gill‐net spawning survey, and a sport fishery survey.ResultOur estimates ofZ ± SE were 0.297 ± 0.019, 0.239 ± 0.009, and 0.205 ± 0.007 for the spring, spawning, and sport fishery surveys, respectively. We suggest that the meanZ ± SE of all survey estimates of 0.247 ± 0.027 would be a reasonable estimate for this population, which equates to a total annual mortality of 22 ± 3%. This estimate is in the low range of rates reported for the species and is in the same range as other populations in the Great Lakes with well‐established natural reproduction.ConclusionWe concluded that these low total mortality rates contributed to the reproductive success in southern Lake Michigan through increasing spawning stock density and age structure and that previous estimates of another important population parameter, the instantaneous natural mortality rateM, were too high. Estimates ofMranged from 0.210 to 0.240 and were based on the Pauly equation, a growth‐ and temperature‐based estimator. We suggest maximum‐age‐based estimators ofMare more appropriate for Lake Trout. Several alternative maximum‐age‐based estimators produced estimates forMof 0.132–0.058, all of which are more compatible with our estimate ofZ.

Evaluation of the influence of correcting for gillnet selectivity on the estimation of population parameters.

Gill nets are a common sampling technique in inland and marine fisheries. However, gill nets are size selective and may result in bias estimates of population parameters. As such, selectivity is commonly assessed using indirect estimation techniques. Indirect estimates of gillnet selectivity have been suggested to improve estimates of important populations metrics (e.g., total annual mortality), but this assertion has not been assessed. In the current study, we simulated hypothetical populations of channel catfish Ictalurus punctatus, lake trout Salvelinus namaycush, walleye Sander vitreus, and white crappie Pomoxis annularis and sampled the populations based on published gillnet encounter and retention probabilities. Total annual mortality and von Bertalanffy parameters were then estimated using unadjusted (not "correcting" for selectivity processes) and adjusted ("correcting" for selectivity processes) age and(or) length data to evaluate the value of accounting for gillnet selectivity when estimating these metrics. Our results indicate that adjusting for retention and encounter probabilities rarely leads to improved estimates of total annual mortality, K, and L∞. For instance, estimates of annual mortality of lake trout based on age data adjusted for retention probability resulted in an overestimate of A by 14.4%. As such, we suggest that analysis of gillnet selectivity only be used when specific questions are being addressed (e.g., catch-at-age models) or in situation when all processes contributing to gillnet selectivity (e.g., contact probability, size-specific availability) are known.

Short‐term effects of wildfire on high elevation stream‐riparian food webs

Understanding how wildfires affect food web structure and function remains an important challenge, especially at high elevations that historically have burned infrequently. In particular, fires may alter the magnitude of reciprocal cross‐ecosystem subsidies, leading to indirect effects on aquatic and terrestrial consumers. We quantified characteristics of high‐elevation (2500–3000 m) stream‐riparian food webs at 10 locations in the southern Rocky Mountains less than one year following high‐intensity, stand‐replacing wildfires. Using a paired ‘burned−unburned' stream survey design, we assessed benthic periphyton, aquatic macroinvertebrate community structure, trout population characteristics, trout stomach contents, inputs and emergence of insects to and from streams, and abundance of predatory riparian spiders that consume aquatic insects. Benthic macroinvertebrate density, flux of emerging aquatic insects, and riparian spider abundances were lower at burned sites. Fluxes of insect inputs entering the stream did not differ with burn status, despite the loss of riparian vegetation due to fire. Trout were somewhat less abundant, but larger on average at burned sites and did not differ in body condition. These results suggest mortality of smaller trout from fire disturbance and/or recolonization of burned sites by larger individuals. Trout showed subtle changes in diet composition with burn status, but no change in biomass or number of prey consumed. In general, burned sites showed greater variation in community characteristics than unburned sites, which may reflect differences in the timing and magnitude of post‐fire flooding, erosion, and scouring of the stream bed. Taken together, our results suggest that short‐term effects of fire disturbance strongly altered some food web responses, but others appeared relatively resilient, which is notable given the high severity of the wildfires in the study area.

Dynamic immune response in the spleens of rainbow trout (Oncorhynchus mykiss) to infectious hematopoietic necrosis virus revealed by transcriptome and immune-related genes expression analysis

Rainbow trout (Oncorhynchus mykiss) is, economically, one of the most important cultured fish in the world. Infectious hematopoietic necrosis virus (IHNV) is a serious pathogen causing high morbidity and mortality in rainbow trout. To gain more insight into the immune response of rainbow trout to the virus, RNA sequencing technology was used to examine the transcriptome profiles in spleens of trout infected and uninfected with IHNV. A total of 9144 differentially expressed genes (DEGs) were identified, of which 3274 were upregulated and 5870 were downregulated. The expression levels of 13 DEGs were validated by quantitative real-time PCR. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis showed that most DEGs were significantly enriched in major immune terms such as immune system process, immune effector process, response to stimulus and key immune signaling pathways. Moreover, we detected the expression levels of six key immune-related genes based on transcriptomic data and protein–protein interaction analysis in four important immune signaling pathways at 0, 6, 12, 24, 48, 72, 96, 120, and 144 h post-infection, including Toll-like receptor signaling pathway (TLR2 and TLR5M), RIG-I-like receptor signaling pathway (TRIM25), NOD-like receptor signaling pathway (RIPK2 and A20) and JAK-STAT signaling pathway (SOCS2). Results revealed that the immune-related genes in these pathways were involved in the antiviral immune response. Altogether, this study provides a better understanding of the dynamic immune response of rainbow trout infected with IHNV, which will lay a foundation for further study of molecular mechanisms of anti-IHNV innate immunity.

Assessing the occurrence of egg stranding for trout and salmon in a regulated river

AbstractA key challenge in many regulated rivers is to define adequate flow levels to protect aquatic organisms. Provisioning of suitable flow can be pivotal bottlenecks for fishes such as salmon and trout that use the riverbed as an incubation habitat. Additionally, the locations where females spawn will define the probability that embryos will be dewatered during the incubation period in a regulated flow regime. We investigated the water flow, dewatering, and incubation mortality in Atlantic salmon and brown trout in natural nests over 19 years in the regulated Bjoreio River in western Norway. During the study period, different flow strategies were applied to mitigate the dewatering of incubating salmon and trout embryos. Average survival in nests sampled in late winter ranged from 54% to 92% among years and was significantly correlated with the minimum water flow occurring during the incubation period. Mortality was significantly higher in nests in shallow areas, reflecting nests exposed to dewatering. The results demonstrate a strong link between incubation mortality and managed flow regimes for river spawning salmonids. Using detailed information on the nest location and incubation mortality, we estimate minimum flow requirements for this river and demonstrate an approach to effectively mitigate the impact of river regulations on embryo survival in Atlantic salmon and brown trout.

Rotenone induces mortality of invasive Lake Trout and Rainbow Trout embryos

AbstractObjectiveNonnative fish, including Lake Trout Salvelinus namaycush and Rainbow Trout Oncorhynchus mykiss, are actively invading lakes and streams and threatening Cutthroat Trout O. clarkii and other native species in the western United States. Programs have been implemented to suppress invasive trout using netting, trapping, electrofishing, angling, or other traditional capture methods. Because these methods are costly and primarily target older, free‐swimming life stages, development of new suppression methods that target embryos on spawning areas is desired to increase suppression efficacy and reduce long‐term costs.MethodsWe evaluated the capability of rotenone, N‐methylpyrrolidone, diethylene glycol ethyl ether, sodium chloride, calcium carbonate, and gelatin to induce mortality of Lake Trout and Rainbow Trout embryos in controlled laboratory experiments.ResultExposure to liquid and powdered rotenone formulations for 12 h at 4 mg/L caused 98% ± 0.7 (mean ± SE) and 99% ± 0.6 Lake Trout mortality, respectively. Exposure to liquid and powdered rotenone formulations for 12 h at 4 mg/L caused 62% ± 4.7 and 85% ± 3.2 Rainbow Trout mortality, respectively. N‐methylpyrrolidone, diethylene glycol ethyl ether, sodium chloride, calcium carbonate, and gelatin exposures were not effective at increasing embryo mortality of either species.ConclusionDeveloping embryos represent a vulnerable life history stage that can be exploited by targeted applications of rotenone. Incorporating novel suppression techniques that effectively increase mortality of embryos in an integrated pest management approach may enhance effective suppression of invasive fishes.

Factors Affecting Post-Challenge Survival of Flavobacterium psychrophilum in Susceptible Rainbow Trout from the Literature.

Infectious bacterial pathogens are a concern for aquaculture as estimates suggest that billions of US dollars are lost annually in aquaculture due to disease. One of the most prevalent salmonid pathogens is the bacterium Flavobacterium psychrophilum that causes bacterial coldwater disease. We reviewed the published F. psychrophilum literature and conducted a Bayesian analysis to examine large-scale patterns in rainbow trout (Oncorhynchus mykiss) mortality associated with laboratory challenge. We incorporated factors that were common across a majority of the laboratory exposure studies and these included bacterial dose, culture time, exposure method, bacterial isolate, experimental duration, and fish weight. The comparison showed that injection as the exposure method produced higher mortality than bath immersion, bacterial isolates differed in their effect on mortality, and bacterial dose has an interactive effect with fish weight and exposure method. Our comparison allows for inference on factors affecting rainbow trout mortality due to exposure to F. psychrophilum and suggests avenues to further optimize research protocols to better reach study goals.

Growth and mortality of sympatric Atlantic salmon and brown trout fry in fluctuating and stable flows

AbstractSub‐daily fluctuations in streamflow may have adverse effects on the biota downstream of dams in hydropeaking‐regulated rivers. Although the stranding of salmonid fry is one documented effect of hydropeaking, little is known about the species‐specific behavioural and subsequent growth effects of sub‐daily flow fluctuations. We investigated the effects of sub‐daily flow fluctuation on growth, mortality and behaviour of sympatric Atlantic salmon (Salmo salar) and brown trout (S. trutta) fry (29–34 mm) in a laboratory experiment. The fluctuating flow treatment negatively affected growth and increased mortality for trout but not for salmon. The level of aggressive behaviour was similar in the fluctuating‐ and stable‐flow treatments. Within the fluctuating flow treatment, there was a trend that more fishes were visibly active above the substrate during low than high flow. These findings suggest that hydropeaking‐induced flow fluctuations may affect fry of different salmonid species in different ways and that brown trout fry may be more vulnerable to hydropeaking effects than Atlantic salmon fry. It can therefore be important to consider the possibility of divergent reactions by different fish species under hydropeaking situations and to incorporate species‐specific strategies to conserve culturally and economically relevant riverine fish species.

Early or Simultaneous Infection with Infectious Pancreatic Necrosis Virus Inhibits Infectious Hematopoietic Necrosis Virus Replication and Induces a Stronger Antiviral Response during Co-infection in Rainbow Trout (Oncorhynchus mykiss).

Infectious hematopoietic necrosis (IHN) and infectious pancreatic necrosis (IPN) are the most common viral diseases of salmon in aquaculture worldwide. The co-infection of rainbow trout (Oncorhynchus mykiss) with IHN virus (IHNV) and IPN virus (IPNV) is known to occur. To determine the influence of IPNV on IHNV in co-infection, rainbow trout were intraperitoneally (i.p.) injected with IPNV at different time intervals prior to, simultaneously to, or after IHNV infection. The replication of IHNV in the brain, gill, heart, liver, spleen, and head kidney was detected by real-time quantitative polymerase chain reaction (qRT-PCR). The results showed that when rainbow trout were i.p. injected with IPNV prior to, simultaneously to, or after IHNV on 2 day (d), IHNV replication was inhibited (p < 0.05) in all collected tissues. Nevertheless, when rainbow trout were i.p. injected with IPNV after IHNV on 7 d (H7P), IHNV replication was only inhibited (p < 0.05) in the liver 14 d post-IHNV infection. Moreover, stronger antiviral responses occurred in all challenge groups. Our results suggest that IPNV can inhibit IHNV replication before or simultaneously with IHNV infection, and induce a stronger antiviral response, and that this inhibition is most sensitive in the liver. Early i.p. injection of IPNV can significantly reduce the mortality of rainbow trout, compared with the group only injected with IHNV.

Supplementation of Dietary Crude Lentinan Improves the Intestinal Microbiota and Immune Barrier in Rainbow Trout (Oncorhynchus mykiss) Infected by Infectious Hematopoietic Necrosis Virus.

The effects of crude lentinan (CLNT) on the intestinal microbiota and the immune barrier were evaluated in rainbow trout (Oncorhynchus mykiss) infected by infectious hematopoietic necrosis virus (IHNV). The results showed that supplementary CLNT declined the rainbow trout mortality caused by IHNV, which suggested that CLNT has preventive effects on IHNV infection. IHNV destroyed intestinal integrity, as well as caused the intestinal oxidative and damage in rainbow trout. Supplementary CLNT significantly strengthened the intestinal immune barrier by declining intestinal permeability, as well as enhancing intestinal antioxidant and anti-inflammatory abilities in IHNV-infected rainbow trout (P<0.05). In addition, CLNT modified the aberrant changes of intestinal microbiota induced by IHNV, mainly represented by promoting the growths of Carnobacterium and Deefgea and inhibiting Mycobacterium and Nannocystis. Especially, supplementing with CLNT significantly promoted the growth of short-chain fatty acid–producing bacteria (P<0.05) and consequently increased the production of acetic acid, butanoic acid, and hexanoic acid in the intestine of IHNV-infected rainbow trout. Furthermore, it was speculated that CLNT could regulate the self-serving metabolic pathways of intestinal microbiota induced by IHNV, such as fatty acid metabolism and amino acid metabolism. Together, CLNT played the antiviral effects on IHNV infection through strengthening the intestinal immune barrier, as well as regulating intestinal microbiota and SCFA metabolism in rainbow trout. The present data revealed that CLNT exerted a promising prebiotic role in preventing the rainbow trout from IHNV infection.

Toxicity of Wildland Fire-Fighting Chemicals in Pulsed Exposures to Rainbow Trout and Fathead Minnows.

Intrusions of fire-fighting chemicals in streams can result from containment and suppression of wildfires and may be harmful to native biota. We investigated the toxicity of seven current-use fire-fighting chemicals to juvenile rainbow trout (Oncorhynchus mykiss) and fathead minnows (Pimephales promelas) by simulating chemical intrusions under variable field conditions to provide insights into the potential damage these chemicals may cause in waterways. In three separate attenuated exsposure assays in which chemical concentration decreased throughout the 96-h exposure period, we variedwater flow rate, water hardness, and initial concentration of test chemical. In an additional series of four pulsed exposure assays in which fish encounter chemical for up to 1 h followed by an observation period in control water, we altered concentration of test chemical, water temperature, duration of chemical exposure, and number of exposures to determine delayed toxicity or recovery. Mortality of rainbow trout was higher across treatments at a warmer temperature and also increased with increasing concentration rate, increasing exposure duration, and sequential exposures across assays. For fathead minnows, mortality increased with increasing concentration of fire retardant and longer exposure durations. Because the ratio of toxic un-ionized ammonia to ionized ammonia is greater with increasing temperature and pH, future studies could investigate the effects of water temperature and pH on native fishes under environmentally relevant concentrations of fire-fighting chemicals. Environ Toxicol Chem 2022;41:1711-1720. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.

Branchitis and mortality in rainbow trout Oncorhynchus mykiss exposed to iron oxidizing bacteria: Diagnostics and management in a Colorado hatchery

AbstractA public trout hatchery in Colorado recorded repeat episodes of morbidity and mortality in early life stages of Rainbow Trout (Oncorhynchus mykiss) stocks. The water source for the affected tanks is a groundwater well with a pH of 6.3 and a ferrous iron concentration of 120 µg/L. Iron oxidizing bacteria (FeOB) were suspected as the underlying cause due to insoluble red particulate matter (iron oxide precipitate) in the water, and the presence of thick red slime (biofilm) that coated tanks and pipes of the facility and adhered to gills, opercula, and fins of fry. On necropsy, gill and fin clippings from moribund fish had mats of adherent red‐orange material. Histopathology revealed severe diffuse proliferative branchitis. There was abundant debris including granular to sheath‐like and stalk‐like pigmented material within the oral and branchial chambers, intimately associated with gill filaments. A Gram preparation demonstrated florid Gram‐negative bacteria within this debris. A Perls’ Prussian blue preparation revealed colocalization of abundant iron. Bacteria were identified morphologically to be of the iron oxidizing bacterial genera Gallionella and Leptothrix. This is the first known report of disease in fish associated with iron‐oxidizing bacteria.