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At least 919 records · Page 51Linked to original sources

USGS1996

Efficacy of formalin, hydrogen peroxide, and sodium chloride on fungal-infected rainbow trout eggs

Antifungal agents are essential for the maintenance of healthy stocks of fish and their eggs in intensive aquaculture operations. In the USA, formalin is the only fungicide approved for use in fish culture. However, hydrogen peroxide and sodium chloride have been granted low regulatory priority drug status by the United States Food and Drug Administration (FDA) and their use is allowed. We evaluated the efficacy of these fungicides for controlling fungal infections on rainbow trout eggs. A pilot study was conducted to determine the minimum water flow rate required to administer test chemicals accurately in Heath incubators. A minimum water flow rate of 7.6 1 min −1 was necessary to maintain treatment concentrations during flow-through chemical exposures. The antifungal activity of formalin, hydrogen peroxide, and sodium chloride was evaluated by treating uninfected and 10% fungal-infected ( Saprolegnia parasitica ) rainbow trout eggs ( Oncorhynchus mykiss ) for 15 min every other day until hatch. There were no significant differences among treatments in percent hatch or final infection for uninfected eggs receiving prophylactic chemical treatments. Eggs of the negative control group (uninfected and untreated) had a mean hatch exceeding 86%. All chemical treatments conducted on the infected egg groups controlled the spread of fungus and improved hatching success compared with the positive control groups (infected and untreated). Formalin treatments of 1000 and 1500 μl l −1 and hydrogen peroxide treatments of 500 and 1000 μl l −1 were the most effective. Sodium chloride treatments of 30 000 mg l −1 improved fry hatch, but the compound was less effective at inhibiting fungal growths compared with hydrogen peroxide and formalin treatments.

Aquaculture↗

USGS1986

Effect of injected rotenone on the production and composition of urine from the rainbow trout (Salmo gairdneri)

Renal function was evaluated in adult rainbow trout (Salmo gairdneri) dosed i.a. with rotenone at 225 and 275 μg/kg. The chemical composition of urine samples and urine flow rates collected over a 5-h pretreatment period were compared with hourly urine samples collected over a 5-h posttreatment period. Significant increases in osmolality and in concentrations of sodium, potassium, chloride, glucose, and total protein were observed in the urine of treated fish. Urine solute concentrations reached maximum values within 1 to 3 h after treatment and decreased thereafter, indicating that the effects were reversible. Concentrations of sodium and chloride were highly correlated in 2-h posttreatment urine samples at the low ( r = 0.922) and high ( r = 0.981) rotenone treatments. Urine flow rates were reduced in trout at each dose of rotenone but the decrease in volume of urine voided was not dose-dependent. In a separate study, [ 14 C]polyethylene glycol was used as a filtration marker to determine the effect of rotenone treatment (225 &mu:g/kg) on urine flow rate, glomerular filtration rate, and renal water reabsorption. We showed that posttreatment urine flow rates were reduced partly by reduced glomerular filtration and partly by increased water reabsorption. Transient increases in plasma osmolality and hematocrit also were observed 0.5 h after rotenone treatment.

Aquatic Toxicology↗

USGS1986

Tissue distribution and elimination of rotenone in rainbow trout

The fate of a single i.v. dose (120 μg/kg) of the piscicide [ 14 C]rotenone was evaluated in rainbow trout for periods up to 72 h after dosing. Rotenone was rapidly cleared from the plasma; less than 2% of the dose remained in the plasma compartment after 20 min. The highest concentrations of rotenone residues (% dose/g tissue) were in the hepatobiliary system, bile, intestine, and in heart, lateral line swimming muscle, and posterior kidney; tissues that are highly dependent on oxidative metabolism. Although rotenone activity was present in all cell fractions examined, greater than 40% was associated with the mitochondrial fraction of liver, kidney, and muscle. More than 85% of the activity extracted from these tissues, except the liver, was parent rotenone. Elimination from whole body and major tissue depots conformed to simple first-order kinetics; the estimated half-life from whole body was 68.5 h. Branchial elimination accounted for 5% of the injected dose over a 4-h period, and urinary elimination was less than 2% over a 48-h period. Rotenone was eliminated essentially unchanged across the gills; however, parent rotenone was not found in either urine or bile. More than 80% of the activity in both urine and bile eluted from HPLC chromatographs as a highly polar fraction that was not hydrolyzed by incubation with either β-glucuronidase or sulfatase. The results imply that hepatobiliary excretion is the major route of elimination for rotenone residues in the trout and that metabolism to a more polar form is a prerequisite for elimination in both the bile and the urine

Aquatic Toxicology↗

USGS1986

Response of rainbow trout to source and level of supplemental dietary methionine

1. Methionine and total sulfur amino acid (TSAA) requirements of rainbow trout ( Salmo gairdneri ) were investigated by feeding graded isosulfurous levels of l - and dl -methionine, l -cystine, and the free acid and calcium forms of methionine hydroxy analog (MHA). 2. Added cystine did not promote growth, survival or prevent cataracts. 3. l -methionine produced fastest growth, followed by dl -methionine, CaMHA and free acid MHA. 4. Trout fed CaMHA gained 85.7 and 92.3% as much as those fed l -methionine and dl -methionine. 5. Within each experiment, the level of L-methionine isomer that prevented cataracts was constant (1.86 g/100g protein in experiment (1), 1.45 in experiment (2) and was lower than for maximum growth (2.89 and 2.15 g) regardless of methionine source.

Comparative Biochemistry and Physiology, Part A: P↗

USGS1983

Branched-chain amino acid aminotransferase activity in the tissues of lake trout

1. The enzyme branched-chain amino acid aminotransferase (BCAT) was found in five tissues of fingerling lake trout, Salvelinus namaycush , (listed in order of decreasing tissue specific activity): posterior kidney, skeletal muscle, gill, liver, and anterior kidney. 2. This pattern is consistent with that found in other animals. 3. The results of this study seem to indicate that BCAT in the liver of lake trout has a higher specific activity than that of the rat and that the specific activity is higher in both the liver and skeletal muscle than it is in these organs of the chick.

Comparative Biochemistry and Physiology, Part B: C↗

USGS1975

Residue dynamics of quinaldine and TFM in rainbow trout

Study of the residue dynamics of 2-methylquinoline (quinaldine) and 3-trifluoromethyl-4-nitrophenol (TFM) in rainbow trout yielded the following findings: 1. Uptake and distribution of TFM by trout was influenced by the biotransformation of the lipidsoluble free phenol. No such effect was observed with quinaldine. 2. Disappearance of quinaldine and TFM from gallbladder bile was slower than from plasma or muscle during 24 hr of withdrawal in fresh water. 3. The concentration of TFM conjugate may exceed that of free TFM in bile by a factor of 10 3 .

General Pharmacology↗

USGS1991

Digestibility and energy values of intact, disrupted and extracts from brewer's dried yeast fed to rainbow trout (Oncorhynchus mykiss)

Although fish meal has historically been used as the primary source of protein in fish feeds, brewer's dried yeast (BDY) is presently being investigated as a primary replacement for fish meal. As little is known about the ability of fish to utilize BDY, studies were conducted to study bioavailability of intact BDY as well as several fractions derived from the disrupted yeast to rainbow trout. Dried BDY was fed to rainbow trout and digestibility and energy values were determined. When the yeast cells were fully disrupted, the absorption of nitrogen increased by more than 20% and the metabolizable energy of the yeast by more than 10%. Energy and nitrogen digestibility were further increased after the removal of all wall material and separation of nitrogen into amino acid and nucleic acid fractions. Disruption of the cell wall significantly increased the nutritional value of BDY for salmonid fishes. The findings suggest that further research be conducted on the use and economy of BDY as a primary nitrogen source in fish feeds.

Animal Feed Science and Technology↗

USGS1993

Chemical and nutritional evaluation of soya protein preparations as primary nitrogen sources for rainbow trout (Oncorhynchus mykiss)

Five soya-bean preparations that had been subjected to various physicochemical processing procedures were chemically defined in respect to proximate analysis, amino acid analyses, protease inhibitor activity, soluble oligosaccharides and antigenicity. These soya preparations were then formulated, along with a low-temperature fish meal control, into six isonitrogenous and isocaloric experimental diets. The diets were fed to rainbow trout ( Oncorhynchus mykiss ) in feeding trials as well as in tests using specially constructed metabolic chambers. Based on the chemical and biological results, we concluded that soya-bean oligosaccharides do not have to be removed or modified for maximum growth or nitrogen utilization by rainbow trout. Likewise, the protease or trypsin inhibitor activity, which was low for all experimental treatments, did not appear to be a major factor in determining fish performance. Although the results regarding naturally occurring soya antigens only suggested allergenicity, it is concluded that more attention should be focused on these heat-stable proteins with antigenic or allergenic potential in fish diets.

Animal Feed Science and Technology↗

USGS2013

Cutthroat trout virus as a surrogate in vitro infection model for testing inhibitors of hepatitis E virus replication

Hepatitis E virus (HEV) is one of the most important causes of acute hepatitis worldwide. Although most infections are self-limiting, mortality is particularly high in pregnant women. Chronic infections can occur in transplant and other immune-compromised patients. Successful treatment of chronic hepatitis E has been reported with ribavirin and pegylated interferon-alpha, however severe side effects were observed. We employed the cutthroat trout virus (CTV), a non-pathogenic fish virus with remarkable similarities to HEV, as a potential surrogate for HEV and established an antiviral assay against this virus using the Chinook salmon embryo (CHSE-214) cell line. Ribavirin and the respective trout interferon were found to efficiently inhibit CTV replication. Other known broad-spectrum inhibitors of RNA virus replication such as the nucleoside analog 2′-C-methylcytidine resulted only in a moderate antiviral activity. In its natural fish host, CTV levels largely fluctuate during the reproductive cycle with the virus detected mainly during spawning. We wondered whether this aspect of CTV infection may serve as a surrogate model for the peculiar pathogenesis of HEV in pregnant women. To that end the effect of three sex steroids on in vitro CTV replication was evaluated. Whereas progesterone resulted in marked inhibition of virus replication, testosterone and 17β-estradiol stimulated viral growth. Our data thus indicate that CTV may serve as a surrogate model for HEV, both for antiviral experiments and studies on the replication biology of the Hepeviridae.

Antiviral Research↗

USGS2006

Isoeugenol concentrations in rainbow trout (Oncorhynchus mykiss) skin-on fillet tissue after exposure to AQUI-S™ at different temperatures, durations, and concentrations

AQUI-S™ is a fish anesthetic/sedative approved for use in several countries including Australia, Chile, and New Zealand and is being pursued for use in the United States. Legal use of AQUI-S™ as an anesthetic in U.S. fish culture depends on approval by the U.S. Food and Drug Administration (FDA). To gain approval in the United States, a number of drug attributes must be characterized including (1) depletion of a drug's total residues from edible fillet tissue taken from exposed fish and (2) depletion of one primary drug residue (a marker residue) from the fillet tissue. The marker residue is selected on the basis of data generated during the total residue depletion study. Characterizing marker residue depletion allows the FDA to establish a withdrawal time for exposed fish ensuring total residue concentrations reach safe levels before fish are made available for human consumption in the U.S. Before an AQUI-S™ total residue depletion study could be conducted with rainbow trout ( Oncorhynchus mykiss ), the exposure parameters (water temperature, isoeugenol concentration, and exposure duration) that generate the greatest total AQUI-S™ residues in fillet tissue need to be determined. Rainbow trout were exposed to AQUI-S™ in water temperatures of 7, 12, and 17 °C in one of two static exposure regimens: (1) AQUI-S™ concentrations of 14 mg/L (nominal concentration) with an exposure duration of 60 min or (2) AQUI-S™ concentrations of 34 mg/L (nominal concentration) with an exposure duration of 10 min (exposure conditions based on probable U.S. use regimens). Immediately after the end of an exposure, fish were rinsed, sacrificed, and skin-on fillets removed. The fillets were homogenized with dry ice, the homogenate extracted with acetonitrile, and extracts analyzed for isoeugenol (the active ingredient in AQUI-S™) by liquid chromatography with absorbance detection. At common water temperatures, the tissue concentration of isoeugenol in fillet tissue from fish exposed to 14-mg/L AQUI-S™ for 60 min was significantly greater than the isoeugenol concentration in fillet tissue from fish exposed to 34-mg/L AQUI-S™ for 10 min ( P < 0.01). The isoeugenol concentration (78.8 μg/g) found in fillet tissue from fish exposed to 14-mg/L AQUI-S™ for 60 min at 17 °C was significantly greater than the isoeugenol tissue concentration (57.3 μg/g) generated at 7 °C ( P < 0.01), but was not significantly greater than the isoeugenol tissue concentration (70.7 μg/g) generated at 12 °C ( P = 0.22). AQUI-S™ exposure regimens and exposure temperatures can significantly impact drug residue concentrations in fillet tissue.

Aquaculture↗

USGS2007

Use of avoidance response by rainbow trout to carbon dioxide for fish self-transfer between tanks

Convenient, economical, and reduced labor fish harvest and transfer systems are required to realize operating cost savings that can be achieved with the use of much larger and deeper circular culture tanks. To achieve these goals, we developed a new technology for transferring fish based on their avoidance behavior to elevated concentrations of dissolved carbon dioxide (CO2). We observed this behavioral response during controlled, replicated experiments that showed dissolved CO2 concentrations of 60-120 mg/L induced rainbow trout (Oncorhynchus mykiss) to swim out of their 11 m3 "growout" tank, through a transfer pipe carrying a flow with ???23 mg/L dissolved CO2, into a second 11 m3 "harvest" tank. The research was conducted using separate groups of rainbow trout held at commercially relevant densities (40-60 kg/m3). The average weight of fish ranged from 0.15 to 1.3 kg during the various trials. In all trials that used a constant flow of low CO2 water (???23 mg/L) entering the growout tank from the harvest tank, approximately 80-90% of the fish swam from the growout tank, through the transfer pipe, and into the harvest tank after the CO2 concentration in the growout tank had exceeded 60 mg/L. The fish that remained in the growout tank stayed within the area of relatively low CO2 water at the entrance of the transfer pipe. However, the rate of fish transfer from the growout tank to the harvest tank was more than doubled when the diameter of the transfer pipe was increased from 203 to 406 mm. To consistently achieve fish transfer efficiencies of 99%, water flow rate through the fish transfer pipe had to be reduced to 10-20% of the original flow just before the conclusion of each trial. Reducing the flow of relatively low CO2 water near the end of each fish transfer event, restricted the zone of relatively low CO2 water about the entrance of the fish transfer pipe, and provided the stimulus for all but a few remaining fish to swim out of the growout tank. Results indicate that the CO2 avoidance technique can provide a convenient, efficient, more economical, and reduced labor approach for fish transfer, especially in applications using large and well mixed circular culture tanks. ?? 2007 Elsevier B.V. All rights reserved.

Aquacultural Engineering↗

USGS2005

Physiological response of wild rainbow trout to angling: Impact of angling duration, fish size, body condition, and temperature

This study evaluated the immediate physiological response of wild rainbow trout to catch-and-release angling in the Alagnak River, southwest Alaska. Information was recorded on individual rainbow trout (n = 415) captured by angling including landing time and the time required to remove hooks (angling duration), the time to anesthetize fish in clove oil and withdraw blood, fish length and weight, and water temperature at capture locations. Plasma cortisol, glucose, ions (sodium, potassium, chloride), and lactate were analyzed to determine the effects of angling duration, fish size, body condition, and temperature. Levels of plasma ions did not change significantly during the observed physiological response and levels of plasma glucose were sometimes influenced by length (2000, 2001), body condition (2001), or temperature (2001). Levels of plasma cortisol and lactate in extended capture fish (angling duration greater than 2 min) were significantly higher than levels in rapid capture fish (angling duration less than 2 min). Rapid capture fish were significantly smaller than extended capture fish, reflecting that fish size influenced landing and handling times. Fish size was related to cortisol and lactate in 2002, which corresponded to the year when larger fish were captured and there were longer landing times. Body condition (i.e., weight/length regression residuals index), was significantly related to lactate in 2000 and 2001. Water temperatures were higher in 2001 (mean temperature ± S.E., 13 ± 2 o C) than in 2002 (10 ± 2 o C), and fish captured in 2001 had significantly higher cortisol and lactate concentrations than fish captured in 2002. The pattern of increase in plasma cortisol and lactate was due to the amount of time fish were angled, and the upper limit of the response was due to water temperature. The results of this study indicate the importance of minimizing the duration of angling in order to reduce the sublethal physiological disturbances in wild fish subjected to catch-and-release angling, particularly during warmer water temperatures. It is also important to note that factors such as fish size may influence both the duration of angling and subsequent physiological response.

Fisheries Research↗

USGS2014

In vitro immune functions in thiamine-replete and -depleted lake trout ( Salvelinus namaycush )

In this study we examined the impacts of in vivo thiamine deficiency on lake trout leukocyte function measured in vitro. When compared outside the context of individual-specific thiamine concentrations no significant differences were observed in leukocyte bactericidal activity or in concanavalin A (Con A), and phytohemagglutinin-P (PHA-P) stimulated leukocyte proliferation. Placing immune functions into context with the ratio of in vivo liver thiamine monophosphate (TMP – biologically inactive form) to thiamine pyrophosphate (TPP – biologically active form) proved to be the best indicator of thiamine depletion impacts as determined using regression modeling. These observed relationships indicated differential effects on the immune measures with bactericidal activity exhibiting an inverse relationship with TMP to TPP ratios, Con A stimulated mitogenesis exhibiting a positive relationship with TMP to TPP ratios and PHA-P stimulated mitogenesis exhibiting no significant relationships. In addition, these relationships showed considerable complexity which included the consistent observation of a thiamine-replete subgroup with characteristics similar to those seen in the leukocytes from thiamine-depleted fish. When considered together, our observations indicate that lake trout leukocytes experience cell-type specific impacts as well as an altered physiologic environment when confronted with a thiamine-limited state.

Fish & Shellfish Immunology↗

USGS2020

Gut contents from multiple morphs of lake trout (Salvelinus namaycush) at two offshore shoals in Lake Superior

Four lake trout, Salvelinus namaycush , Walbaum 1792 morphs occur in Lake Superior: lean, siscowet, humper, and redfin. Diets of lean and siscowet have been relatively well described. However, less is known about diets of humper and redfin, and overall few studies have been conducted at offshore shoals. We compared gut content data among mature (357–867 mm) sympatric lake trout morphs caught at two offshore shoals in Lake Superior, Stannard Rock and Superior Shoal, in 2013 and 2014 (total n = 416). All morphs were caught in shallow (<50 m), mid (50–100 m), and deep (>100 m) strata. Invertebrates made up a greater portion of the stomach contents than did fish for all morphs by both percent occurrence and proportional biomass, and Mysis was the primary invertebrate consumed by all morphs at both sites. Coregonus spp. and deepwater sculpin, Myoxocephalus thompsonii were the most commonly consumed fish. Humper had the highest average proportional biomass of deepwater sculpin and had no other identifiable species of fish in their guts. Biomass of fish in redfin guts was highest for Coregonus spp., followed by similar amounts of deepwater sculpin and burbot, Lota lota . Diet overlap among morphs was high, and differences in prey consumption between sites are likely related to prey availability. Additional study is needed to determine if differences in trophic ecology between humper and other morphs are sufficient to support concurrent stocking of multiple morphs, particularly in light of recent declines in native prey fishes, especially Coregonus spp., in the Laurentian Great Lakes.

Lake Superior↗

USGS2024

A comparison of stable isotopes and polychlorinated biphenyls 1 among genetic strains of Lake Ontario lake trout (Salvelinus namaycush)

This study quantified stable carbon (δ 13 C) and nitrogen (δ 15 N) isotopes, polychlorinated biphenyl (PCB) concentrations and growth rates among multiple genetic strains of Lake Ontario lake trout ( Salvelinus namaycush ) to evaluate the potential role of genetics in these parameters. Fish ranging in age from 1 to 31 years ( n = 72) and representing nine genetic strains including wild-recruits to hatchery fish derived from Lakes Ontario, Superior and Champlain watersheds, and individuals of unknown hatchery origin. Carbon (δ 13 C) and nitrogen (δ 15 N) stable isotope values averaged −22.2 ‰ and 17.4 ‰, respectively, but did not differ significantly among genetic strains. ΣPCB concentrations ranged from 42 to 1820 ng/g and varied significantly among individuals including those of similar age and genetic strain. For example, Sum PCB (ΣPCB) concentrations among 7-year-old fish ( n = 16) ranged from 159 to 607 ng/g, which compares to growth rates of 3.5 – 32.9 %/yr for these same fish. Multivariate analysis of stable isotope and PCB profiles, however, provided considerable resolution among the strains. For example, fish of unknown hatchery origin ordinated most similar to Seneca Lake fish, the predominant strain stocked in Lake Ontario. Wild fish had a unique ordination with only Lake Superior Klondike strain fish overlapping into their ordination space. Lakes Champlain and Superior strain individuals had similar ordinations but did not overlap substantially with wild or Klondike strain fish. Combined, these differences agree with the ecologies described for these strains in their native ecosystems suggesting that insight can be gained from strain specific evaluations of ecological tracers and these pollutants among Great Lakes lake trout.

Lake Ontario↗

USGS2025

Evaluation of a recovering lake trout population in Lake Champlain using close-kin mark-recapture and genetic strain assignment

Lake trout ( Salvelinus namaycush ) populations in many northern North American large lake systems have been substantially reduced or extirpated due to overfishing, habitat loss, and introduction of invasive species. Following reductions in fishing pressure and successful suppression of sea lamprey, attempts have been made to restore self-sustaining populations into most of these waters but success has been slow and limited. In contrast, lake-wide lake trout restoration occurred abruptly and rapidly in Lake Champlain after 40 years of stocking, with robust, widespread, and sustained wild recruitment observed from the 2012 cohort onwards. We sought to better understand the dynamics of the recovery success in Lake Champlain using a multi-year tissue dataset, in combination with a recently-designed genotyping panel and close-kin mark-recapture, to quantify the performance (i.e., survival and reproductive success) of stocking sources and strategies with an eye towards informing restoration programs in other systems. We also assessed the overall abundance of adult fish and parental dynamics associated with wild recruitment. Our results indicate that adult survival is remarkably high and overall abundance is low compared to other large lake systems in similar latitudes, with the vast majority of wild recruitment genetically traceable to the Seneca strain fish historically stocked by New York State. We observed little evidence of hybridization between the two strains and close-kin mark-recapture estimates indicated that approximately 20 % of the adult population was contributing to successful recruitment on a regular basis. Ultimately, our results point to a growing wild population that has the potential to become self-sustaining.

New York, Vermont↗

USGS2025

Landscape transcriptomic analysis detects thermal stress responses and potential adaptive variation in wild brook trout (Salvelinus fontinalis) during successive heatwaves

Extreme weather events, such as heatwaves, are becoming more frequent and intense as a result of climate change. Critically, such extreme weather events can be more important drivers of extirpation and selection than changes in annual or seasonal averages and they pose a particularly large threat to poikilothermic organisms. In this study, we evaluated the transcriptomic response of a coldwater adapted fish species, the eastern brook trout ( Salvelinus fontinalis ), to two successive heatwaves during July and August 2022. We sampled brook trout at eight time points from four streams ( N = 116 fish), sequenced mRNA from gill samples using TagSeq, and quantified expression levels of 32,670 unique transcripts. Multivariate analyses found that overall expression patterns in response to water temperature change were similar among streams. These analyses further detected groups of genes involved in immune response and oxygen carrier activity that were upregulated and downregulated respectively at higher water temperatures. We also detected 43 genes that were differentially expressed at different time points and followed the same expression pattern during the two heatwaves. Of these genes, 42 covaried with water temperature and most (27, 62.8 %) exhibited responses that varied by stream. Some of the differentially expressed genes, including heat shock proteins and cold-inducible RNA binding proteins, have been widely linked to temperature responses in experimental studies, whereas other genes we identified have functions that have not been well-studied in relationship to temperature or have unknown functions. This study shows the utility of landscape transcriptomic approaches to identify important biological processes governing wild organismal responses to short-term stressors. The results of this study can guide future investigations to identify phenotypic and genetic diversity that contribute to adaptive responses to heatwaves and improve predictions of how populations will respond to future climate change.

Pennsylvania↗

USGS2017

Replication and shedding kinetics of infectious hematopoietic necrosis virus in juvenile rainbow trout

Viral replication and shedding are key components of transmission and fitness, the kinetics of which are heavily dependent on virus, host, and environmental factors. To date, no studies have quantified the shedding kinetics of infectious hematopoietic necrosis virus (IHNV) in rainbow trout ( Oncorhynchus mykiss ), or how they are associated with replication, making it difficult to ascertain the transmission dynamics of this pathogen of high agricultural and conservation importance. Here, the replication and shedding kinetics of two M genogroup IHNV genotypes were examined in their naturally co-evolved rainbow trout host. Within host virus replication began rapidly, approaching maximum values by day 3 post-infection, after which viral load was maintained or gradually dropped through day 7. Host innate immune response measured as stimulation of Mx-1 gene expression generally followed within host viral loads. Shedding also began very quickly and peaked within 2 days, defining a generally uniform early peak period of shedding from 1 to 4 days after exposure to virus. This was followed by a post-peak period where shedding declined, such that the majority of fish were no longer shedding by day 12 post-infection. Despite similar kinetics, the average shedding rate over the course of infection was significantly lower in mixed compared to single genotype infections, suggesting a competition effect, however, this did not significantly impact the total amount of virus shed. The data also indicated that the duration of shedding, rather than peak amount of virus shed, was correlated with fish mortality. Generally, the majority of virus produced during infection appeared to be shed into the environment rather than maintained in the host, although there was more retention of within host virus during the post-peak period. Viral virulence was correlated with shedding, such that the more virulent of the two genotypes shed more total virus. This fundamental understanding of IHNV shedding kinetics and variation at the individual fish level could assist with management decisions about how to respond to disease outbreaks when they occur.

Virus Research↗