Application of probiotics in trout farms in North-West Russia

In recent years, various probiotic and immunomodulating drugs have been actively used in aquaculture. The group of probiotics includes preparations of the Vetom series, created on the basis of the spore-forming bacteria Bacillus subtilus and Bacillus licheniformis. Recently, a large positive experience has been accumulated in the use of Vetom 1.1 in fish farming. The drug is actively used in trout cage farms in Karelia and the Leningrad region. Vetom 1.1 was administered orally with food at a dosage of 50–75 mg/kg ichthyomass per day for 10 days. An improvement in the epizootic state of fish was observed: regeneration of the affected fins and branchial epithelium, normalization of the blood state. Biocomplex Multibacterin (previously in research — Multibacterin OMEGA-10) is a functional food based on lactobacillus (Lactobacillus acidophilus). The drug has a high antagonistic activity against microorganisms — pathogens of bacterial etiology, stimulates the synthesis of immunoglobulins, improves metabolic processes in the body of animals, and stimulates regeneration processes. Multibacterin is recommended for introduction into trout feed in case of toxicosis, bacterial and fungal infection at a dosage of 0.1 ml/kg of ichthyomass for 10 days. The study of the effect of the Multibacterin biocomplex on the state of rainbow trout of different age groups, reared under different conditions, was carried out. With the introduction of the probiotic Multibacterin into the feed, a decrease in the death of fish was noted to 9.5% versus 20% in the control. An improvement in the state of the branchial epithelium was revealed, and the development of the regenerative process on the affected branchial lobes was noted. These preparations help to maintain the immunity of fish and can be recommended for use in aquaculture.

Chorion Alterations in Eyed-Stage Salmonid Eggs Farmed in La Araucanía, Chile: A Retrospective Study

The chorion is the primary envelop that protects the fish embryo against mechanical actions, pathogens, and abrupt changes in physical and chemicals conditions of the incubation medium. During embryo development, chorion alterations are not rare, but the occurrence of these is scarcely reported. Increased frequency of chorion alterations can result in increased embryo mortality and thus decreased reproductive performance and losses for fish farms. In this study, we characterize different chorion alterations observed in samples collected over 14 years from 12 salmon and trout farms located in the region of La Araucanía in southern Chile, which sent live eyed-stage embryos (‘eyed-eggs’) for quality analysis to our laboratory. We found soft chorion as the most common alteration observed, being present in the whole 14-year series analyzed in Atlantic Salmon (Salmo salar) and affecting up to 35.0% of the samples examined in a year. This alteration also affected up to 20.0 and 5.7% of Coho Salmon (Oncorhynchus kisutch) and Rainbow Trout (Oncorhynchus mykiss) samples analyzed in a year, respectively. We also found an increase of other chorion alterations, including perforated and white-spotted chorion in Atlantic and Coho Salmon, in the last 8 years. Among the three species, Rainbow Trout exhibited fewer chorion alterations. As the embryonated eggs analyzed here were obtained from broodstocks maintained under standard industrial conditions, these alterations might be linked to changes in environmental conditions affecting the incubation water that need to be further investigated.

Evaluation of Potential Transfer of the Pathogen Saprolegnia parasitica between Farmed Salmonids and Wild Fish

Saprolegnia infections are among the main parasitic diseases affecting farmed salmonids. The distribution and potential transfer of Saprolegnia spp. between farms and the natural environment has been scarcely investigated. Therefore, this work aimed to study the diversity and abundance of oomycete species in salmonid farms, tributary water, and effluent water systems. Four trout farms in Italy and two Atlantic salmon farms in Scotland were considered. In Italian farms, 532 isolates of oomycetes were obtained from fish and water, at upstream, inside, and downstream the farms. In Scottish farms, 201 oomycetes isolates were obtained from water outside the farm and from fish and water inside the farming units. Isolates were identified to the species level through amplification and sequencing of the ITS rDNA region. In Italy, S. parasitica was significantly more present in farmed than in wild fish, while in water it was more frequently isolated from the wild, particularly in effluent systems, not associated with more frequent isolation of S. parasitica in wild fish downstream the farm. In Scotland, S. parasitica was the most prevalent species isolated from fish, while isolates from water were mostly Pythium spp. with few S. parasitica isolates from upstream and downstream the farms.

Dual-Organ Transcriptomic Analysis of Rainbow Trout Infected With Ichthyophthirius multifiliis Through Co-Expression and Machine Learning

Ichthyophthirius multifiliis is a major pathogen that causes a high mortality rate in trout farms. However, systemic responses to the pathogen and its interactions with multiple organs during the course of infection have not been well described. In this study, dual-organ transcriptomic responses in the liver and head kidney and hemato-serological indexes were profiled under I. multifiliis infection and recovery to investigate systemic immuno-physiological characteristics. Several strategies for massive transcriptomic interpretation, such as differentially expressed genes (DEGs), Poisson linear discriminant (PLDA), and weighted gene co-expression network analysis (WGCNA) models were used to investigate the featured genes/pathways while minimizing the disadvantages of individual methods. During the course of infection, 6,097 and 2,931 DEGs were identified in the head kidney and liver, respectively. Markers of protein processing in the endoplasmic reticulum, oxidative phosphorylation, and the proteasome were highly expressed. Likewise, simultaneous ferroptosis and cellular reconstruction was observed, which is strongly linked to multiple organ dysfunction. In contrast, pathways relevant to cellular replication were up-regulated in only the head kidney, while endocytosis- and phagosome-related pathways were notably expressed in the liver. Moreover, interestingly, most immune-relevant pathways (e.g., leukocyte trans-endothelial migration, Fc gamma R-mediated phagocytosis) were highly activated in the liver, but the same pathways in the head kidney were down-regulated. These conflicting results from different organs suggest that interpretation of co-expression among organs is crucial for profiling of systemic responses during infection. The dual-organ transcriptomics approaches presented in this study will greatly contribute to our understanding of multi-organ interactions under I. multifiliis infection from a broader perspective.

Antimicrobial Susceptibility Profiles and Resistance Genes in Genus Aeromonas spp. Isolated from the Environment and Rainbow Trout of Two Fish Farms in France

This study presents the occurrence and abundance of Aeromonas antibiotic-resistant bacteria (ARB) and genes (ARGs) isolated from water, biofilm and fish in two commercial trout farms before and one week after flumequine treatment. Wild (WT) and non-wild (NWT) strains were determined for quinolones (flumequine, oxolinic acid and enrofloxacin), oxytetracycline (OXY), florfenicol (FFN), trimethoprim-sulfamethoxazole (TMP) and colistin (COL), and pMAR (presumptive multi-resistant) strains were classified. Forty-four ARGs for the mentioned antibiotics, β-lactams and multi-resistance were quantified for 211 isolates. BlaSHV-01, mexF and tetE were the dominant ARGs. A greater occurrence and abundance of tetA2, sul3, floR1, blaSHV-01 and mexF were observed for NWT compared to WT. The occurrence of pMAR and NWT Aeromonas for quinolones, OXY, FFN, TMP, COL and ARGs depended on the Aeromonas origin, antibiotic use and the presence of upstream activities. Our results revealed the impact of a flumequine treatment on Aeromonas present on a fish farm through an increase in NWT and pMAR strains. The link between fish and their environment was shown by the detection of identical ARB and ARGs in the two types of samples. There appears to be a high risk of resistance genes developing and spreading in aquatic environments.

Molecular Epidemiology of Novirhabdoviruses Emerging in Iranian Trout Farms

Novirhabdoviruses cause large epizootics and economic losses of farmed trout. In this study, we surveyed Viral hemorrhagic septicemia virus and Infectious hematopoietic and necrosis virus (VHSV and IHNV) through both monitoring and investigation of clinical outbreaks reported by farmers in the regions with major rainbow trout production in Iran from 2015 to 2019. RT-PCR assays of the kidney samples and cell culture (EPC/FHM cells) samples confirmed the presence of the viruses, with 9 VHSV and 4 IHNV isolates, in both endemic and new areas of Iran. Sequence analysis of the G gene revealed that VHSV isolates belonged to genogroup Ia, and IHNV isolates were clustered into genogroup E, both typical for isolates from European countries. A haplotype analysis based on non-homologous amino acids of the G gene supports the emergence of two lineages of IHNV from clade 1 (E-1), as well as VHSV clade 2 (Ia-2) of the European genogroups, confirming that VHSV and IHNV isolates in Iran, have originated from Europe possibly via imported eggs.

Lactococcus garvieae Isolates from Rainbow Trout (Oncorhynchus mykiss, W.) Compared by PLG and SA1B10 PCR Primer Pairs

The aim of this study was to identify and compare Lactococcus garvieae strains using the PLG primer pair and SA1B10 primer pair. Also, the antibiotic resistance of the strains was investigated in the study. For this aim, commercial trout farms at Kemer, Korkuteli, and Manavgat, Antalya Province, Turkey were visited every month from June to September 2018. Thirty sick fish were sampled in the study. Lethargy, anorexia, darkening of skin color, unilateral or bilateral exophthalmos, opacification and hemorrhages in the eyes of the sick fish, and abdominal dropsy were observed. At necropsy, hemorrhages in the internal organs, splenomegaly, and darkening of the spleen and ascites were present. Seventy-five strains from sick fish samples verified on the basis of the biochemical characterization and PCR studies. The strains showed homogeneity in terms of phenotypic characteristics and all strains were identified as Lactococcus garvieae. The PCR technique was applied to 50 of 75 strains using PLG primer pair. While 47 of 50 strains gave positive results, amplification was not observed in 3 strains. When the PCR technique using SA1B10 primer pair was applied to a total of 25 strains, 3 of which were negative, 22 of which gave positive amplification, and 25 strains gave positive results. Resistance was determined by the disk diffusion method. All seventy-five strains were resistant to ampicillin and all strains were susceptible to bacitracin and tetracycline. It was found that the resistance and susceptibility of the strains showed variation to other antibiotics used in the study.Keywords: Lactococcus garvieae; Rainbow Trout; PCR; Antibiotic