In this study, effects of Aloe vera (Aloe barbadensis) on growth performance, hematology and serum biochemical properties, non-specific immune responses, gene expressions related to innate immunity, ...and resistance against Saprolegnia parasitica pathogenesis were studied in rainbow trout for 8 weeks. Aloe vera powder at concentrations of 0, 5, 10, and 15 g/kg were added to a basal diet. Fish were fed three times a day during the 8 weeks. At the end of feeding period, the fish were exposed to the oomycete S. parasitica for 3 weeks. The results showed that all treatments fed with Aloe vera-included diets showed significant increases in growth performance (weight gain, specific growth rate and low feed efficiency) compared to the control. Feeding the fish with 15 g/kg of dietary Aloe vera resulted in better hematology indices (red and white blood cell counts, and concentrations of hematocrit and hemoglobin), serum biochemical parameters (total protein, albumin, and globulin), and non-specific immunity indices (respiratory burst activity, lysozyme activity and complement system) in comparison with the other treatments and control. Furthermore, fish fed 10 and 15 g/kg of dietary Aloe vera showed up-regulation of TNF-α, IL-1b, IL-6 and IL-8 gene expression compared to the control. A significant reduction in mortality was observed in the treated fish with 15 g/kg of Aloe vera compared to the control following challenging with S. parasitica. The use of Aloe vera powder, particularly at a level of 15 g/kg, in rainbow trout diet was observed to improve growth and immunity parameters as well as boost fish resistance against S. parasitica contamination.
•15 g/kg of dietary Aloe vera was more effective on hematology and non-specific immunity indices.•The results showed that fed with Aloe vera showed significant increases in cytokine gene expiration.•The use of Aloe vera powder in rainbow trout diet was increased fish resistance against Saprolegnia parasitica contamination.
The effect of serial in vitro subculturing on three pathogenic strains of Saprolegnia parasitica was investigated. The isolates were passed through Atlantic salmon, Salmo salar L. parr, and then ...re‐isolated as single spore colonies. All strains caused infection. The isolate obtained from diseased fish served as a virulent reference culture and was designated ‘AP’ (‘activated through passage’). Successive subculturing was made by obtaining an inoculum from AP to produce the 2nd subculture and then passaged to the 3rd subculture (from the 2nd), until the 15th passage was obtained. Spores used to produce storage cultures were collected at passages 5, 10 and 15. The different passages of each strain were used to artificially infect Atlantic salmon parr. Morphological characterization of growth patterns was performed to observe differences occurring due to serial in vitro subculturing. Two of the strains declined in virulence after 15 successive in vitro subcultures, whereas one did not. This study is the first to investigate attenuation of virulence in Saprolegnia and whether or not isolates of S. parasitica should be passed through the fish host prior to challenge experiments. It reveals that some strains degenerate more rapidly than others when subjected to successive in vitro subculturing on glucose–yeast extract.
Oomycetes are eukaryotic pathogens infecting animals and plants. Amongst them Saprolegnia parasitica is a fish pathogenic oomycete causing devastating losses in the aquaculture industry. To secure ...fish supply, new drugs are in high demand and since fish experiments are time consuming, expensive and involve animal welfare issues the search for adequate model systems is essential. Galleria mellonella serves as a heterologous host model for bacterial and fungal infections. This study extends the use of G. mellonella for studying infections with oomycetes. Saprolegniales are highly pathogenic to the insects while in contrast, the plant pathogen Phytophthora infestans showed no pathogenicity. Melanisation of hyphae below the cuticle allowed direct macroscopic monitoring of disease progression. However, the melanin response is not systemic as for other pathogens but instead is very local. The mortality of the larvae is dose-dependent and can be induced by cysts or regenerating protoplasts as an alternative source of inoculation.
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•Galleria mellonella serves as a heterologous host model system for Saprolegniales.•The melanisation of the larvae is local around the growing hyphae.•Regenerating protoplasts can be used as an alternative inoculum to cysts.
Captive animal populations, be it for food production or conservation programmes, are often maintained at densities far beyond those in natural environments, which can have profound effects on ...behaviour, immune and stress levels, and ultimately welfare. How such alterations impact transcriptional responses to pathogen infection is a 'different kettle of fish' and remains poorly understood. Here, we assessed survival and gene expression profiles of infected fish reared at two different densities to elucidate potential functional genomic mechanisms for density-related differences in disease susceptibility.
Utilising a whole-transcriptome sequencing (RNAseq) approach, we demonstrate that rearing density in tilapia (Oreochromis niloticus) significantly impacts susceptibility to the oomycete Saprolegnia parasitica, via altered transcriptional infection responses. Tilapia held at low densities have increased expression of genes related to stress, likely due to increased aggressive interactions. When challenged with Saprolegnia, low-density fish exhibit altered expression of inflammatory gene responses and enhanced levels of adaptive immune gene suppression compared to fish reared at higher density, resulting in significantly increased mortality rates. In addition, Saprolegnia infection substantially perturbs expression of circadian clock genes, with fish reared at low-density having higher levels of molecular clock dysregulation.
Our results reveal the wide-scale impact of stocking density on transcriptional responses to infection and highlight the need to incorporate circadian biology into our understanding of disease dynamics in managed animals.
Many fishes possess specialized epidermal cells that are ruptured by the teeth of predators, thus reliably indicating the presence of an actively foraging predator. Understanding the evolution of ...these cells has intrigued evolutionary ecologists because the release of these alarm chemicals is not voluntary. Here, we show that predation pressure does not influence alarm cell production in fishes. Alarm cell production is stimulated by exposure to skin-penetrating pathogens (water moulds: Saprolegnia ferax and Saprolegnia parasitica), skin-penetrating parasites (larval trematodes: Teleorchis sp. and Uvulifer sp.) and correlated with exposure to UV radiation. Suppression of the immune system with environmentally relevant levels of Cd inhibits alarm cell production of fishes challenged with Saprolegnia. These data are the first evidence that alarm substance cells have an immune function against ubiquitous environmental challenges to epidermal integrity. Our results indicate that these specialized cells arose and are maintained by natural selection owing to selfish benefits unrelated to predator-prey interactions. Cell contents released when these cells are damaged in predator attacks have secondarily acquired an ecological role as alarm cues because selection favours receivers to detect and respond adaptively to public information about predation.
Infectious diseases represent an important barrier to sustainable aquaculture development. Rearing density can substantially impact fish productivity, health and welfare in aquaculture, including ...growth rates, behaviour and, crucially, immune activity. Given the current emphasis on aquaculture diversification, stress-related indicators broadly applicable across species are needed. Utilising an interspecific comparative transcriptomic (RNAseq) approach, we compared gill gene expression responses of Atlantic salmon (Salmo salar) and Nile tilapia (Oreochromis niloticus) to rearing density and Saprolegnia parasitica infection. Salmon reared at high-density showed increased expression of stress-related markers (e.g. c-fos and hsp70), and downregulation of innate immune genes. Upon pathogen challenge, only salmon reared at low density exhibited increased expression of inflammatory interleukins and lymphocyte-related genes. Tilapia immunity, in contrast, was impaired at low-density. Using overlapping gene ontology enrichment and gene ortholog analyses, we found that density-related stress similarly impacted salmon and tilapia in key immune pathways, altering the expression of genes vital to inflammatory and Th17 responses to pathogen challenge. Given the challenges posed by ectoparasites and gill diseases in fish farms, this study underscores the importance of optimal rearing densities for immunocompetence, particularly for mucosal immunity. Our comparative transcriptomics analyses identified density stress impacted immune markers common across different fish taxa, providing key molecular targets with potential for monitoring and enhancing aquaculture resilience in a wide range of farmed species.
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•Salmo salar reared at high density show higher expression of stress-related markers.•On pathogen challenge, density impacts salmon immune gene expression responses.•Salmon and Nile tilapia have contrasting “stressful” densities.•Density-related stress similarly impacted salmon and tilapia in key immune pathways.•Teleost markers of density-impacted immunity may include inflammatory and Th17 genes.
The present investigation estimated the potential anti-oomycetes activity of Thymus linearis leaf extract and identified the phytochemical compounds by Gas chromatography-Mass spectrometry (GC-MS). ...Saprolegnia parasitica isolated from the golden mahseer, Tor putitora was used for efficacy study. The effect of T. linearis plant extract on hyphal growth, zoospore production was employed by a agar diffusion method and microwell plate, respectively. The ethanolic extract of T. linearis exhibited hyphal growth inhibition to 54.45 ± 0.9% at 0.32 mg ml−1 and complete inhibition (100%) at 5.12 mg ml−1. The zoospore production was ultimately arrested at 0.32 mg ml−1 against S. parasitica. A total of 18 volatile constituents were identified from the GC–MS of the whole plant extract. The major volatile constituents in the extracts were ethyl (9z, 12z)-9, 12-octadecadienoate (22.58%), palmitic acid (11.95%), ethyl palmitate (9.89%), phytol (5.03%), stigmast-5-En-3-Ol, (3.Beta.)- (4.54%), (Z, Z)-6, 9-Cis-3, 4-epoxy-nonadecadiene (3.60%), carvacrol (3.59%), cryptomeridiol (3.22%), Heptadecanoic acid, ethyl ester (2.03%) and naphthalene, decahydro-(1.28%). Molecular docking was performed by Auto Dock Vina 4.0 of the constituents for obtaining the binding mode predictions with target proteins of S. parasitica. Phytol and carvacrol were identified to interact with plasma membrane ATPase, host target protein-1 and TKL protein kinase and V-type protein ATPase. Molecular interaction of phytol was stronger to V-type protein ATPase. From the results, it is evident that T. linearis contain various natural compounds and is recommended plant of phytopharmaceutical importance. T. linearis extract could be explored as antioomycetes compounds for treating oomycetes infections, saprolegniasis in aquaculture.
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•Ethanolic extract of Thymus linearis exhibited Saprolegnia parasitica growth inhibitory activity•Profiles of the phyto-constituents of T. linearis plant extract was obtained using GC-MS.•Binding mode predictions of carvacrol and phytol was performed through molecular modelling.•T. linearis extract could be explored as anti-oomycetes agent in aquaculture.
spp. water molds severely impact fish health in aquaculture, fish farms and hobby fish tanks colonizing mature and immature stages of fishes, as well as eggs. Considering that there are no drugs ...licensed for treating and/or control the organism, efficient and environmental low-impact methods to control these oomycetes in aquaculture are needed. The aim of the present report was to evaluate the in vitro sensitivity of
to essential oils (EOs) from
L.,
Risso et Poiteau,
Burm. f.,
Macfad,
Osbeck,
Blume,
(Nees ex Steud.) Watson,
Mill.,
Hook.f.,
(Lour.) Pers.,
L.,
L.,
L'Hér.,
Merr. & L.M.Perry, and
L., by microdilution test. The most effective EOs assayed were
and
, followed by
and
These EOs could be of interest for controlling
infections. Nevertheless, further safety studies are necessary to evaluate if these products could be dispersed in tank waters, or if their use should be limited to aquaculture supplies.
In this study, effects of nettle (Urtica dioica) on growth, immunity, and gene expressions were examined in rainbow trout after an 8-week feeding period. A total of 264 juvenile rainbow trout ...(10.72 ± 0.55 g) were selected and stocked randomly in 12 aquaria. Nettle powder was added to the fish feed at three doses, 0.5,1 and 1.5% served as treatments. At the end of 8-week feeding period, the fish were exposed to Saprolegnia parasitica for 3 weeks. Results showed that all treatments fed with nettle diets exhibited significant increases in weight gain and SGR, and decreased FCR compared to the control. Feeding the fish with dietary nettle resulted in significant rises in blood indices and non-specific immunity in comparison with the control. Furthermore, fish fed 0.5% of dietary nettle showed significantly increased expressions of TNF-α, IL-1b, IL-6 and IL-8 genes following 8 weeks of feeding. A significant reduction in mortality rate was observed in the fish treated with 0.5% of nettle compared to the control following challenging with S. parasitica. Our observations indicate that the use of 0.5% nettle powder in rainbow trout diet can improve growth and immunity parameters as well as fish resistance against S. parasitica contamination.
•The rainbow trout fed with nettle (Urtica dioica) diets exhibited significant increases in growth parameters.•Fish fed 0.5% of dietary nettle showed significantly increased expressions of TNF-α, IL-1b, IL-6 and IL-8 genes.•Reduction in mortality was observed in the fish treated with 0.5% of nettle after challenge with Saprolegnia parasitica.
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