Mortality Of Rainbow Trout Research Articles

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.

Lack of Effect of Biowish Multibio 3PS Probiotic on Bacterial Cold-Water Disease-Induced Mortality in Rainbow Trout

Flavobacterium psychrophilum, the causative agent of Bacterial Cold-Water Disease (BCWD) is prevalent in salmonid hatcheries worldwide.

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

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.

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.

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.

NANOPARTICLES TOXICITY IN FISHES

Nanoparticles have a size between 1 to 100 nm. Nanoparticles have applications in the production of agrifood, biomedical products, fertilizers, herbicides, pesticides, sensors, food processing, food packaging, nutraceuticals, diagnosis, drug delivery and treatment of diseases. Nanoparticles easily enter the environment unimpeded, entering soil, water and air through various anthropogenic activities. In water, fishes quickly ingest or inhale these nanoparticles. Due to their small size, nanoparticles easily enter the body and affect various tissues, and they also easily cross the blood-brain barrier. This results in different toxic effects on the fishes, an essential part of our ecosystem. Studies and research on fishes have revealed that various nanoparticles damage the gills, liver, intestine, brain, and enzyme system of fishes. They also lead to decreased heart rate, curvatures of the axis, delayed or early hatching, osmoregulatory failure, and genotoxic effects in fishes. Cerium oxide nanoparticles induced fish mortality in Rainbow trout at an initial concentration of 10 \(\mu\)g/L in tap and green waters. Studies on cell lines of various fish species such as rainbow trout, fathead minnow, zebrafish, goldfish, and haddock have proved that Silica nanoparticles are toxic to their epithelial tissues of skin and gills. These findings agree with similar human and mouse cell studies reported to date. If the nanoparticles accumulate in the fish tissue and the same fishes are consumed by the organisms from other trophic levels, the nanoparticles accumulate, leading to biomagnification. The release of nanoparticles in the environment must be checked and reduced. And further detailed research needs to be carried out on the effects of nanoparticles in fishes, humans, and other animals.

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.

The Opportunistic Pathogen Chryseobacterium balustinum WLT: Pathogenicity and Antibiotic Resistance

This study aimed to re-evaluate the pathogenic characteristics of Chryseobacterium balustinum, generally known as a food spoilage bacterium. We observed mass mortality in a rainbow trout farm in Jeonbuk province, Republic of Korea. Fewer studies have reported on rainbow trout mortality or infections in Korea than in other countries; among these, few studies have reported cases of Chryseobacterium infections. Sequencing analysis revealed that this bacterium is closely related (99.24%) to Chryseobacterium balustinum. Bacterial identification assays, including the API test, sequencing, and phylogenetic analysis, found the 24 isolates to be C. balustinum. The strain showed multiple resistance to 18 of 25 antibiotics tested. Primary clinical symptoms of its infection are damage to the fins, necrosis, and cytoplasmic vacuolation in hepatocytes. The pathogenicity of the strain was determined following Koch’s postulates and the challenge test. The present results suggest that C. balustinum WLT can be considered a multidrug-resistant zoonotic pathogen responsible for mortality and economic losses.

Transcriptome Analysis in the Head Kidney of Rainbow Trout (Oncorhynchus mykiss) Immunized with a Combined Vaccine of Formalin-Inactivated Aeromonas salmonicida and Vibrio anguillarum.

This study aimed to identify the molecular mechanisms regulated by a combined vaccine against Aeromonas salmonicida and Vibrio anguillarum (O1 serotype). These bacteria cause furunculosis and vibriosis, respectively, and are associated with a high mortality in rainbow trout in Korea. The vaccine upregulated gene expression of TCRα, T-bet, sIgM, and mIgM, markers of an activated adaptive immune response. On days 1, 3, and 5, transcriptome analysis revealed 862 (430 up- and 432 downregulated), 492 (204 up- and 288 downregulated), and 741 (270 up- and 471 downregulated) differentially expressed genes (DEGs), respectively. Gene ontology (GO) enrichment analysis identified 377 (108 MF, 132 CC, 137 BP), 302 (60 MF, 180 CC, 62 BP), and 314 (115 MF, 129 CC, 70 BP) GOs at days 1, 3, and 5, respectively. Kyoto Encyclopedia of Genetic and Genomic enrichment analysis identified eight immune system-related pathways like cytokine-cytokine receptor interaction, NF-kappaB signaling pathway, TNF signaling pathway, NOD-like receptor signaling pathway, cytosolic DNA sensing pathway, cell adhesion molecule, complement and coagulation cascade, and antigen processing and presentation. In the analysis of the protein–protein interaction of immune-related DEGs, a total of 59, 21, and 21 interactional relationships were identified at days 1, 3, and 5, respectively, with TNF having the highest centrality at all three time points.

Hooking and Handling Mortality of Trout Captured in the Bald Eagle Creek Trout Tournament, Pennsylvania

AbstractFor many years bait has been banned in catch‐and‐release trout fisheries owing to anticipated high rates of hooking mortality. Recent studies that have been conducted in streams have found relatively low rates of hooking mortality. The objective of this study was to quantify the rates of hooking and handling mortality of stocked trout that were caught by recreational anglers using the terminal tackle of their choice during a 2‐d tournament for three consecutive years on a small stream in central Pennsylvania. Each year, we affixed T‐bar anchor tags to more than 800 Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, Rainbow Trout Oncorhynchus mykiss, and golden Rainbow Trout and stocked them in an 11‐km stream reach. All of the tagged trout that were alive when they were checked in were eligible for cash prizes. After processing, the trout were monitored for 9 d in a hatchery. Anglers brought in 423–591 tagged trout each year. The rates for hooking and handling mortality among years ranged from 3.9% to 8.0%. Mortality of Rainbow Trout (7.4%) was the highest among the three species. The trout were caught on natural and manufactured baits (87.9%), artificial lures (10.8%), and flies (1.3%); mortality was not related to terminal tackle. Trout that had hooks left embedded in them or had blood in their holding container had the highest mortality. Time from capture to check‐in, holding method, hook type, or hook size did not influence mortality. This study demonstrated low mortality of trout that were caught primarily with bait and subjected to more handling stress than they would normally experience in catch‐and‐release waters. We suggest that these results support the notion that bait fishing can be allowed without negative population‐level effects in streams where regulations require that most or all angled trout are released.

Insights on the toxicity of selected rare earth elements in rainbow trout hepatocytes

The increasing extraction of rare earth elements (REEs) for technology applications raised concerns for contamination and toxicity in the environment. The purpose of this study was to examine the toxicity of the following REEs in primary cultures of rainbow trout hepatocytes: yttrium (Y), samarium (Sm), gadolinium (Gd), terbium (Tb) and lutetium (Lu). Hepatocytes were exposed to increasing concentrations of the above elements for 24 h at 15 °C and they were analyzed for viability, metallothioneins (MT), glutathione-S-transferase (GST) and arachidonate cyclooxygenase (COX) as markers of oxidative stress and inflammation. The results revealed that the cytoxicity of REEs were as follows in decreasing order: Y > Sm > Lu > Tb > Gd in concordance with published rainbow trout mortality data. While effects on GST and COX activities were marginal, MT levels were more strongly increased with the 2 most toxic REEs (Y and Sm) and Gd, while MT levels were decreased in the least toxic ones (Tb, Lu). While cell viability followed published trout mortality data, it also followed the redox potential and the glutathione affinity constant (log k). The capacity to induce/decrease MT levels was associated with ionic radius, log k (glutathione) and electronegativity. A proposed mechanism of toxicity for REEs is presented based on the chemical properties of REEs, namely the glutathione binding constant and ionic radius, in light of the observed effects in trout hepatocytes.

Horizontal transmission of Piscirickettsia salmonis from the wild sub-Antarctic notothenioid fish Eleginops maclovinus to rainbow trout (Oncorhynchus mykiss) under experimental conditions.

Piscirickettsia salmonis is the aetiological agent of piscirickettsiosis, a bacterial disease that affects farmed salmonids, causing high mortalities and significant economic losses in the Chilean salmon farm industry. Given the Chilean native fish species Patagonian blenny, Eleginops maclovinus, lives in the vicinity of salmon farms, it is relevant to clarify the epidemiological role that this species could play in the transmission and/or dissemination of this pathogen. This study aimed to evaluate the bidirectional transmission of P.salmonis between the Patagonian blenny and Oncorhynchus mykiss (rainbow trout), via a cohabitation challenge model. The results of this study demonstrated the transmission of the bacteria from Patagonian blennies to rainbow trout, considering the specific mortality in cohabitant rainbow trout, reaching 46%: the necropsy of these specimens, evidencing the characteristic pathological lesions of the disease and the positive results of the qPCR analysis for P.salmonis, in the same individuals. In contrast, no mortalities of Patagonian blenny specimens were recorded in the challenged experimental groups. This study is the first report showing the horizontal transmission of P.salmonis from a native non-salmonid species, such as the Patagonian blenny, to a salmonid species, generating the disease and specific mortality in rainbow trout, using a cohabitation challenge.

Autumn lipid reserves, overwinter lipid depletion, and high winter mortality of rainbow trout in experimental lakes

Accumulation of lipid reserves is considered important for the overwinter survival of many animals. Fish are thought to deplete lipids until they reach a critical minimum below which starvation mortality occurs, meaning that lipid-dependent selective overwinter mortality may be a strong selective pressure leading to life-history evolution favouring lipid accumulation and storage. Much of our current knowledge comes from either laboratory studies or field studies that are not well controlled, but rarely is overwinter survival directly estimated to evaluate selective mortality. Here, we studied patterns of lipid storage, overwinter lipid depletion, and subsequent survival of a single strain of rainbow trout (Oncorhynchus mykiss) stocked into experimental lakes that differed in productivity but experienced the same local winter conditions. Productive lakes produced trout with higher lipid content and steeper allometric slopes in contrast with trout in low food lakes; however, these field-based values were all substantially lower than those determined in the lab. Surviving trout from low productivity lakes emerged from winter in poor condition, close to the expected critical minimum needed for survival, in comparison with survivors from higher-productivity lakes. As expected, overwinter mortality was lipid-dependent, with fish in low food lakes nearing 90% mortality and about 60% mortality in high food lakes. Importantly, these estimates are higher than from laboratory (∼70%) and modelling studies (0% to 14%) for this species. These results, though from stocked populations, suggest winter mortality is an even stronger selective pressure than previously thought, creating a tight population bottleneck in young fish cohorts and likely promoting life-history strategies that favour energy storage at the expense of somatic growth.

Pharmacological iron-chelation as an assisted nutritional immunity strategy against Piscirickettsia salmonis infection

Salmonid Rickettsial Septicaemia (SRS), caused by Piscirickettsia salmonis, is a severe bacterial disease in the Chilean salmon farming industry. Vaccines and antibiotics are the current strategies to fight SRS; however, the high frequency of new epizootic events confirms the need to develop new strategies to combat this disease. An innovative opportunity is perturbing the host pathways used by the microorganisms to replicate inside host cells through host-directed antimicrobial drugs (HDAD). Iron is a critical nutrient for P. salmonis infection; hence, the use of iron-chelators becomes an excellent alternative to be used as HDAD. The aim of this work was to use the iron chelator Deferiprone (DFP) as HDAD to treat SRS. Here, we describe the protective effect of the iron chelator DFP over P. salmonis infections at non-antibiotic concentrations, in bacterial challenges both in vitro and in vivo. At the cellular level, our results indicate that DFP reduced the intracellular iron content by 33.1% and P. salmonis relative load during bacterial infections by 78%. These findings were recapitulated in fish, where DFP reduced the mortality of rainbow trout challenged with P. salmonis in 34.9% compared to the non-treated group. This is the first report of the protective capacity of an iron chelator against infection in fish, becoming a potential effective host-directed therapy for SRS and other animals against ferrophilic pathogens.

Citrus flavonoids, β-Glucan and organic acid feed additives decrease relative risk during Yersinia ruckeri O1 biotype 2 infection of rainbow trout (Oncorhynchus mykiss).

Whether through direct supplementation of bacteria or by prebiotic supplementation thought to favour subsets of bacteria, modulation of gut microbiota constitutes an important and promising alternative to the use of prophylactic and growth promoting antibiotics in worldwide aquaculture. We fed a commercial base feed, alone or supplemented with either proprietary β-glucan, β-glucan and organic acids, citrus flavonoid or yeast cell wall supplements, to rainbow trout over a period of four weeks. Fish from each feed group were then subjected to experimental, waterborne infection with Yersinia ruckeri O1 biotype 2. Following experimental feeding, the β-glucan and organic acids supplemented group showed significantly improved feed conversion and lipid efficiency ratios. Furthermore, the β-glucan, β-glucan and organic acids and citrus flavonoid supplements proved to significantly reduce the risk of mortality in rainbow trout during experimental infection as shown by hazard ratio analysis. Resulting in 33.2%, 30.6% and 30.5% reduction in risk relative to the non-supplemented base feed, respectively, these three supplements show a promising potential either as stand-alone feed supplements, or as components in complex feed formulations.

Dietary Polygonum minus extract ameliorated the growth performance, humoral immune parameters, immune-related gene expression and resistance against Yersinia ruckeri in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the effects of Polygonum minus extracts on growth performance, skin mucus and serum immune parameters as well as immune-related gene expressions in rainbow trout. For this purpose, rainbow trout (mean weight: 50 ± 2.2 g) were fed experimental diets containing different levels 0 (control), 5, 10 and 15 mg/kg diet of P. minus for 8 weeks. At the end of the trial, the results showed that final body weight, weight gain and specific growth rate were significantly increased in fish fed diets containing P. minus (P < 0.05). In addition, the feed conversion ratio of fish treated with P. minus was significantly decreased (P < 0.05) compared to the control group. The blood RBCs, WBCs, Hb, total protein, albumin, and globulin showed a significant increase with decreased alkaline phosphatase (ALP) and alanine aminotransferase (ALT) in fish treated with P. minus compared to the control treatment. The blood lysozyme activity and total Ig showed significantly higher values in fish fed P. minus at 10 or 15 mg/kg than the other groups, while the respiratory burst activity increased significantly in fish fed P. minus at 15 mg/kg diet than the other groups (P < 0.05). The skin mucus total protein and esterase increased significantly in fish fed P. minus at 15 mg/kg diet than the other groups (P < 0.05), while the skin mucus alkaline phosphatase, protease and lysozyme activity increased significantly in fish fed P. minus at 10 or 15 mg/kg diet than the other groups (P < 0.05). The relative immune gene expressions (IL-1β, IL-8, and lysozyme) upregulated relatively in fish fed P. minus at 15 mg/kg diet than the other groups. The relative expression of TNF-α upregulated in fish fed P. minus at 10 or 15 mg/kg diet. The cumulative mortality of rainbow trout subjected to Yersinia ruckeri infectious exhibited relatively low mortality levels in all supplemented groups with the lowest being in fish fed 15 mg/kg P. minus. Highest percentage survival (%) rate was found in the 15 mg P. minus per kg diet. The results of this study confirm the beneficial effects of dietary P. minus on growth performance and immune parameters of rainbow trout.