Antagonism of Aeromonas hydrophila by propolis and its effect on the performance of Nile tilapia, Oreochromis niloticus

Dietary propolis improves the growth performance, redox status, and immune response of Nile tilapia upon a cold-stress challenge

The purpose of this research was to demonstrate the potential of adding propolis (PR) to the diet of Nile tilapia (Oreochromis niloticus) to mitigate the harmful effect of cold stress (CS) on the growth performance, redox status, and immunological response. Two trials were conducted in this study. First, 210 Nile tilapia fingerlings (28.61±0.20 g) were used in a preliminary trial to determine the appropriate PR level and supplementation period to be applied for the main trial. Fish were assigned into 7 treatment groups (3 aquaria replicates × 10 fish per aquarium in each treatment group) according to the rate of PR supplementation in the fish diets at 0, 2, 4, 6, 8, 10, and 12 g/kg for 6 consecutive weeks. The average body weight and body weight gain were determined weekly. It was found that PR supplementation at 10 g/kg in fish diet for 4 weeks was enough to obtain significant results on the growth performance of Nile tilapia. For the main trial of the present study, 480 Nile tilapia fingerlings (average weight 29.93±0.11 g) were distributed into randomized 2 PR × 2 CS factorial treatment groups (6 replicate aquariums containing 20 fish in each group). Fish of PR groups received a basal diet for a feeding period of 4 weeks, included with 10 g/kg PR (+ PR group) or without PR inclusion (- PR group). Fish of the CS groups were either challenged with cold stress at 18°C (+ CS group) or maintained at a temperature of 26°C during the feeding period (- CS group). The results showed that CS challenge significantly (p < 0.05) impaired the growth indices, redox status, and immune response in the challenged fish compared to the non-challenged fish. On contradictory, the inclusion of PR into fish diets enhanced (p < 0.05) the feed intake, growth indices, antioxidant enzyme activity, and immunological parameters. Moreover, PR treatment alleviated the CS deterioration of fish weights, specific growth rates, feed efficiency, antioxidant enzyme activity, lymphocyte proliferation, and phagocytosis activity and alleviated the elevated mortality, H/L ratio, and malondialdehyde levels by cold stress. It is concluded that the inclusion of propolis at 10 g/kg in the diet of Nile tilapia fish could be approved as a nutritional approach to enhance their performance, especially when stressed by low-temperature conditions.

Dietary propolis complementation relieves the physiological and growth deterioration induced by Flavobacterium columnare infection in juveniles of common carp (Cyprinus carpio)

The current study was proposed to explore the role of dietary propolis (PR) supplementation in alleviating the negative effects of columnaris disease (CD) challenge on the growth performance, plasma biochemicals, antioxidant activity, stress indicators, and immunological reactions of common carp (Cyprinus carpio) fish. Five hundred forty common carp juveniles were evenly placed in thirty-six 100-L tanks and stocked for acclimatization to the lab conditions with a control diet within a started period of 14 days. Fish (average initial weight of 7.11±0.06 g) were randomly distributed into one of six treatment groups (6 replicate tanks × 15 fish per tank in each treatment group). Fish in the first group was assigned as a negative control without CD challenge or PR supplementation. Fish in the other five groups were challenged with CD by immersion of fish for 60 min into a 10-L water bath supplemented with 6×106 CFU/mL (median lethal dose, LD50) of pathogenic F. columnare bacteria. After infection, the fish were restored to their tanks and fed on a basal diet supplemented with PR at 0, 3, 6, 9, or 12 g/kg diet. The experimental period continued for 6 consecutive weeks in which the feed was introduced twice a day (8:00 and 15:00 h) at a rate of 2% of the fish biomass. Ten percent of water was siphoned and renewed after each meal every day, in addition to 50% of water refreshment after cleaning the tank every three days. The tanks were continuously aerated and provided with standard rearing conditions for carp fish (24.0±1.12°C, 7.7±0.22 pH, 6.3±0.16 mg/L O2, and 14L/10D photoperiod). The growth performance traits such as feed intake (FI), weight gain (WG), final weight (FW), specific growth rate (SGR), feed efficiency (FE), and cumulative mortality rates (CM) were recorded during the experimental period. At the end of the trial, blood samples were obtained from the fish to evaluate some plasma biochemicals, including aspartate aminotransaminase (AST), alanine aminotransferase (ALT), creatinine (CRE), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH), antioxidant biomarkers, including total antioxidant capacity (TAOC), total superoxide dismutase (TSOD), reduced glutathione (rGSH), and catalase (CAT), stress indicators, including heterophil to lymphocyte (H/L) ratio, cortisol (COR), malondialdehyde (MDA), and myeloperoxidase (MPO), and immunological reactions, including peripheral blood leukocyte proliferation (PBLP), phagocytosis activity (PHG), lysozyme activity (LYS), alternative complement hemolytic action (ACH50), and total immunoglobulin concentration (TIG). In addition, samples of infected fish gills were taken to quantify the number of F. columnare in the PR-supplemented groups using the quantitative real-time polymerase chain reaction (qPCR) technique. The results showed that incorporating PR into the dietary ingredients of common carp has a protective effect against the challenge with F. columnare infection. There were linear and quadratic positive trends (P < 0.05) in most parameters of growth performance, plasma biochemicals, antioxidant activity, stress indicators, and immunological reactions with the increased PR-supplemented levels in the diet of infected fish. The best results were obtained when using PR at 9 g/kg in the diet, while higher levels (12 g/kg PR) showed an adverse trend in the evaluated parameters. The FI, WG, FW, SGR, and FE were improved by approximately 37, 104, 34, 73, and 49% in the fish treated with 9 g/kg PR compared to none-PR-infected fish. In addition, adding PR at the 9 g/kg diet level was the best dose that reduced the H/L ratio, COR, MDA, and MPO by about 14, 52, 48, and 29%, respectively, in the infected fish. Furthermore, the mortality rate was reduced by 94%, and the number of pathogenic bacteria cells adherent to the fish gills was lowered by 96% in the infected fish treated with 9 g/kg PR compared to none-PR infected fish. Our results concluded that dietary supplementation with 9 g/kg PR could be a promising nutritional approach for improving the growth performance, physiological profile, and health status of common carp fish, particularly when challenged with F. columnare or similar bacterial infections.

Review on Propolis Applications in Food Preservation and Active Packaging

Propolis is a natural hive product collected by honeybees from different plants and trees. The collected resins are then mixed with bee wax and secretions. Propolis has a long history of use in traditional and alternative medicine. Propolis possesses recognized antimicrobial and antioxidant properties. Both properties are characteristics of food preservatives. Moreover, most propolis components, in particular flavonoids and phenolic acids, are natural constituents of food. Several studies suggest that propolis could find use as a natural food preservative. This review is focused on the potential application of propolis in the antimicrobial and antioxidant preservation of food and its possible application as new, safe, natural, and multifunctional material in food packaging. In addition, the possible influence of propolis and its used extracts on the sensory properties of food is also discussed.

Immunoprotective role of aloin and disease resistance in Labeo rohita, infected with bacterial fish pathogen, Aeromonas hydrophila

The effect of aloin on mucosal immune response and disease resistance was elucidated in Labeo rohita infected with the bacterial fish pathogen, Aeromonas hydrophila. Fishes were divided into four groups: (i) control, (ii) vehicle control, (iii) bacteria infected and (iv) bacteria infected and aloin treated. Fish were intraperitoneally injected with A. hydrophila suspension at the dose of 2 × 10⁶ CFU/fish at 0 day (d). Following bacterial injection at 0 d, fish were treated with aloin at a dose of 1 mg/kg body weight intraperitoneally at an interval of 24 h for 4 consecutive days. Mucus collected from fish of each group was analyzed at 2 d, 4 d, 6 d, 8 d and 10 d. In bacteria-infected fish, a significant decrease (P < 0.05) in the activity of certain enzymatic and non-enzymatic immune parameters was observed. The activity of these immune parameters showed a gradual recovery on administration of aloin in bacteria-infected fish. Cumulative mortality was also found to be low in the aloin-treated group as compared to that in the infected group. Thus, aloin could act as an immunostimulant and play a protective role against disease caused by bacteria.

Establishment of Epidemiological Cut-Off Values and the Distribution of Resistance Genes in Aeromonas hydrophila and Aeromonas veronii Isolated from Aquatic Animals

The emergence of antimicrobial-resistant bacteria is an enormous challenge to public health. Aeromonas hydrophila and Aeromonas veronii are opportunistic pathogens in fish. They exert tremendous adverse effects on aquaculture production, owing to their acquired antibiotic resistance. A few Clinical and Laboratory Standards Institute (CLSI) epidemiological cut-off values (ECVs) against Aeromonas spp. are available. We evaluated antimicrobial susceptibility by establishing 8 ECVs using two analytical methods, normalized resistance interpretation and ECOFFinder. We detected antimicrobial resistance genes in two motile Aeromonas spp. isolated from aquatic animals. Results showed that 89.2% of A. hydrophila and 75.8% of A. veronii isolates were non-wild types according to the oxytetracycline ECV_CLSI and ECV_NRI, respectively. The antimicrobial resistance genes included tetA, tetB, tetD, tetE, cat, floR, qnrA, qnrB, qnrS, strA-strB, and aac(6′)-1b. The most common tet gene in Aeromonas spp. isolates was tetE, followed by tetA. Some strains carried more than one tet gene, with tetA–tetD and tetA–tetE found in A. hydrophila; however, tetB was not detected in any of the strains. Furthermore, 18.6% of A. hydrophila and 24.2% of A. veronii isolates showed presumptive multidrug-resistant phenotypes. The emergence of multidrug resistance among aquatic aeromonads suggests the spread of drug resistance and difficult to treat bacterial infections.

Propolis nanoparticles relieved the impacts of glyphosate-induced oxidative stress and immunosuppression in Nile tilapia

The risk of the waterborne toxicity caused by herbicides threatens the aquatic environment. In this study, propolis nanoparticles were shown to relieve the impacts of glyphosate-induced oxidative stress and immunosuppression in Nile tilapia. The control group was fed a basal diet and maintained in a glyphosate-free water (control). Simultaneously, the other three groups were exposed to sublethal concentrations of glyphosate (0.6 mg/L) and fed diets containing 0 and 10 g propolis and 10 g propolis nanoparticles for 4 weeks. Nile tilapia exposed to glyphosate for 2 and 4 weeks exhibited a significant increase in serum alanine aminotransferase, aspartate aminotransferase, urea, and creatinine values compared to the control. After 2 and 4 weeks, fish exposed to glyphosate who were not fed propolis and propolis nanoparticles showed a significant reduction in total protein, albumin, and globulin levels, lysozyme activity, and total immunoglobulin levels. Nile tilapia exposed to glyphosate displayed a significant increase in blood glucose and cortisol concentrations after 2 and 4 weeks. Furthermore, liver and gill tissues from fish exposed to glyphosate exhibited a significant increase in malondialdehyde (MDA) concentrations. Conversely, a statistically significant decrease was observed in the liver and gill MDA levels and AChE activity of the groups treated with propolis and propolis nanoparticles compared to the groups exposed to glyphosate and fed the basal diet. Fish exposed to glyphosate for 2 and 4 weeks showed a significant decrease (p < 0.05) in hepatic and gill glutathione (GSH) concentration and white blood cell and red blood cell counts compared to the control group. Meanwhile, these parameters in groups fed propolis and propolis nanoparticles were markedly ameliorated compared to exposed fish fed the basal diet. Dietary supplementation of propolis nanoparticles is superior to supplementation of propolis in the normal form for protecting Nile tilapia from glyphosate toxicity.

Bee pollen as a dietary supplement for fish: Effect on the reproductive performance of zebrafish and the immunological response of their offspring

Bee pollen, a natural resource collected by bees, is rich in many nutrients, therefore it may represent a useful dietary supplement. Different uses of bee pollen are proposed due to its beneficial health properties, which includes the capacity to improve animal performance and promote immunostimulation. Animal nutrition can directly affect adults and their offspring, and larval stage is a critical moment for fish due to high mortality related to immune challenges. Thus, the present study attempted to evaluate the effects of adding bee pollen to a zebrafish diet, specifically, analyzing the effects on reproduction and immunity transference to descendants. Zebrafish adults received control diets based on commercial flakes and live food Artemia sp. nauplii or bee pollen-supplemented diets, administered three times a day, at the same time. The animals received the diets over 60 d, and throughout this period, they were tested for: egg production per female, total number of eggs, embryo viability rate, larval survival rate after exposure to spring viremia of carp virus and to Salmonella enterica serovar Typhimurium, and larval neutrophil recruitment after tail wounding. Bee pollen supplementation failed to improve egg production and embryo viability, and was unable to substitute flakes in zebrafish breeders. Instead, the offspring of breeders fed with bee pollen supplemented diets showed longer survival upon virus exposure and higher neutrophil migration to wounds. These results indicate that bee pollen can influence vertical immunity through important mechanisms related to offspring immunity in the early stages, when larval immune system is not fully developed.

Propolis: Properties and composition, health benefits and applications in fish nutrition

Propolis is a viscous, waxy, resinous substance that is produced from the exudates of flowers and buds by the action of salivary enzymes of honey bees. Propolis may differ in color (brown, red or green), with color being influenced by the chemical composition and age of the product. Propolis has a special distinctive odor owing to the high concentration of volatile essential oils. It is composed of 5% pollen grains, 10% essential and aromatic oils, 30% wax, 50% resin and balsams, and other minor trace substances. Natural propolis products may be useful for a range of applications in aquaculture systems instead of relying on the application of synthetic compounds to manage many ailments that affect business profitability. It has been reported in several studies that propolis enhances performance, economics, immunity response and disease resistance in different fish species. This present review discusses the functional actions of propolis and the prospects of its use as an antimicrobial, antioxidant, immune-modulatory, antiseptic, antiparasitic, anti-inflammatory and food additive in aquaculture production. In summary, propolis could be a natural supplement that has the potential to improve fish health status and immunity thereby enhancing growth and productivity of the fish industry as well as economic efficiency.

Oral delivery of pVAX-OMP and pVAX-hly DNA vaccine using chitosan-tripolyphosphate (Cs-TPP) nanoparticles in Rohu, (Labeo rohita) for protection against Aeromonas hydrophila infection

The present study examines the effectiveness of DNA vaccine against Aeromonas hydrophila through oral route using chitosan-tripolyphosphate (Cs-TPP) nanoparticles encapsulation. The virulent gene of outer membrane protein (OMP) and hemolysin (hly) related to pathogenicity of A. hydrophila was used to construct a DNA vaccine using pVAX1, and the construct was named as pVAX-OMP and pVAX-hly DNA vaccines. The pVAX-OMP and pVAX-hly DNA vaccines were encapsulated by Cs-TPP nanoparticles and size measured by field emission scanning electron microscopy (FE-SEM). The encapsulation efficiency of Cs-TPP nanoparticles was found to be 79.6% for pVAX-OMP DNA and 82.3% for pVAX-hly DNA binding with Cs-TPP nanoparticles. The stability and invitro release profile of plasmid DNA was also determined after encapsulation using DNase and chitosanase. DNA vaccines distribution in tissues was investigated in fish fed with the pVAX-OMP, pVAX-hly and pVAX-OMP+pVAX-hly encapsulated in Cs-TPP nanoparticles and confirmed by PCR and multiplex PCR. The results suggest that Cs-TPP nanoparticles encapsulated DNA vaccine delivered into fish by feeding. After oral vaccination of Labeo rohita were challenged with A. hydrophila by intraperitoneal injection. Relatively, gene expression of c- and g-type lysozyme followed by pro- and anti-inflammatory cytokines (Interlukin-10 and Tumor Growth Factor β) was up-regulated in heart and kidney for pVAX-OMP+pVAX-hly vaccinated group. Moreover, fish fed with pVAX-OMP+pVAX-hly encapsulated in Cs-TPP nanoparticles had a significantly higher survival rate (76.2%) against A. hydrophila. This study concludes that pVAX-OMP and pVAX-hly DNA vaccines can be delivered orally using Cs-TPP nanoparticles for protection against A. hydrophilainfection.

Isolation and characterization of two virulent Aeromonads associated with haemorrhagic septicaemia and tail-rot disease in farmed climbing perch Anabas testudineus

Diseased Anabas testudineus exhibiting signs of tail-rot and ulcerations on body were collected from a fish farm in Assam, India during the winter season (November 2018 to January 2019). Swabs from the infected body parts were streaked on sterilized nutrient agar. Two dominant bacterial colonies were obtained, which were then isolated and labelled as AM-31 and AM-05. Standard biochemical characterisation and 16S rRNA and rpoB gene sequencing identified AM-31 isolate as Aeromonas hydrophila and AM-05 as Aeromonas jandaei. Symptoms similar to that of natural infection were observed on re-infecting both bacteria to disease-free A. testudineus, which confirmed their virulence. LC50 was determined at 1.3 × 104 (A. hydrophila) and 2.5 × 104 (A. jandaei) CFU per fish in intraperitoneal injection. Further, PCR amplification of specific genes responsible for virulence (aerolysin and enterotoxin) confirmed pathogenicity of both bacteria. Histopathology of kidney and liver in the experimentally-infected fishes revealed haemorrhage, tubular degeneration and vacuolation. Antibiotic profiles were also assessed for both bacteria. To the best of our knowledge, the present work is a first report on the mortality of farmed climbing perch naturally-infected by A. hydrophila as well as A. jandaei, with no records of pathogenicity of the latter in this fish.

Skin Multi-Omics-Based Interactome Analysis: Integrating the Tissue and Mucus Exuded Layer for a Comprehensive Understanding of the Teleost Mucosa Functionality as Model of Study

From a general structural perspective, a mucosal tissue is constituted by two main matrices: the tissue and the secreted mucus. Jointly, they fulfill a wide range of functions including the protection of the epithelial layer. In this study, we simultaneously analyzed the epithelial tissue and the secreted mucus response using a holistic interactome-based multi-omics approach. The effect of the gilthead sea bream (Sparus aurata) skin mucosa to a dietary inclusion of spray-dried porcine plasma (SDPP) was evaluated. The epithelial skin microarrays-based transcriptome data showed 194 differentially expressed genes, meanwhile the exuded mucus proteome analysis 35 differentially synthesized proteins. Separately, the skin transcripteractome revealed an expression profile that favored biological mechanisms associated to gene expression, biogenesis, vesicle function, protein transport and localization to the membrane. Mucus proteome showed an enhanced protective role with putatively higher antioxidant and antimicrobial properties. The integrated skin mucosa multi-interactome analysis evidenced the interrelationship and synergy between the metabolism and the exuded mucus functions improving specifically the tissue development, innate defenses, and environment recognition. Histologically, the skin increased in thickness and in number of mucous cells. A positive impact on animal performance, growth and feed efficiency was also registered. Collectively, the results suggest an intimate crosstalk between skin tissue and its exuded mucus in response to the nutritional stimulus (SDPP supplementation) that favors the stimulation of cell protein turnover and the activation of the exudation machinery in the skin mucosa. Thus, the multi-omics-based interactome analysis provides a comprehensive understanding of the biological context of response that takes place in a mucosal tissue. In perspective, this strategy is applicable for evaluating the effect of any experimental variable on any mucosal tissue functionality, including the benefits this assessment may provide on the study of the mammalian mucosa.

Alterations in the epidermis of the carp, Labeo rohita (Cyprinidae: Cypriniformes), infected by the bacteria, Aeromonas hydrophila: A scanning electron microscopic, histopathological and immunohistochemical investigation

This study was carried out to comprehend the pathogenicity of the bacteria in the epidermis of Labeo rohita inoculated with Aeromonas hydrophila. Alterations in the histopathology of the epidermis were examined using scanning electron microscopy, light microscopy and the localization of iNOS and caspase 3 + ve cells by means of immunohistochemical methods. Skin samples obtained from infected fish at different intervals 2, 4, 6, 8 and 10 days showed significant changes in the cellular components of the epidermis. Epithelial cells often appeared hypertrophied with fragmented and loosely arranged microridges, and in the process of exfoliation. Mucous goblet cells increased significantly in density. Club cells showed degenerative changes, often with simultaneous confluence of adjacent cells and release of their contents. Increase in density of iNOS and caspase 3 + ve cells indicates inflammatory response and apoptosis. This study could provide valuable information on the pathogenesis of the disease, and disease outbreaks in farmed fish. Further, it could provide useful guidelines for fish farmers to take preventive measures for the control of the disease.

The Inclusion of a Supercritical Fluid Extract, Obtained From Honey Bee Pollen, in the Diet of Gilthead Sea Bream (Sparus aurata), Improves Fish Immune Response by Enhancing Anti-oxidant, and Anti-bacterial Activities

In the present study, the immune-stimulatory effect of two levels of honey bee pollen (5 and 10%, P5 and P10 treatment, respectively) and its supercritical fluid extract (0. 5 and 1%, E0.5 and E1, respectively) included in the diet, was tested in gilthead seabream (Sparus aurata). The in vivo trial was preceded by the evaluation of antioxidant properties of three different bee pollen extracts obtained by water, ethanol 80%, and Supercritic Fluids Extraction (SFE). The preliminary evaluation attested that the SFE showed the lowest extraction yield (10.47%) compared to ethanol 80% (48.61%) and water (45.99%). SFE extract showed good antioxidant properties with high polyphenol content (13.06 mg GAE/g), radical scavenging activity (3.12 mg/ml), reducing power (38.68 mg/mL EC50). On the contrary, the water extract showed the significantly lowest polyphenol content (2 mg GAE/g; P < 0.05). The results of in vivo trial demonstrate that the diets supplemented with SFE bee pollen extract had a stimulatory effect on fish serum immunity, respect to the inclusion of raw pollen, this latter revealing some inhibitory effects in the immune response, such a decrease of serum peroxidase and lysozyme activities, particularly in P10 group significantly different (P < 0.05) from the control group. On the contrary, serum peroxidase, protease, antiprotease, were significantly increased in fish fed the diets supplemented with supercritical fluid extract, respect to the fish fed on control and on diets supplemented with 5 and 10% of raw pollen. For what concerns the bactericidal activity against Vibrio harveyii, all the treatments containing bee pollen regardless of the type showed their serum bactericidal activity significantly increased with respect to the control groups (p < 0.05). Given its high antioxidant properties, the absence of toxic solvents and the positive action carried out on improving the humoral response in gilthead seam bream, honey bee pollen SFE extract can be taken into account in the formulation of fish feeds.

GWAS Analysis Indicated Importance of NF-κB Signaling Pathway in Host Resistance Against Motile Aeromonas Septicemia Disease in Catfish

Motile Aeromonas septicemia (MAS) disease caused by a bacterial pathogen, Aeromonas hydrophila, is an emerging but severe disease of catfish. Genetic enhancement of disease resistance is considered to be effective to control the disease. To provide an insight into the genomic basis of MAS disease resistance, in this study, we conducted a genome-wide association study (GWAS) to identify quantitative trait loci (QTL). A total of 1820 interspecific backcross catfish of 7 families were challenged with A. hydrophila, and 382 phenotypic extremes were selected for genotyping with the catfish 690 K SNP arrays. Three QTL on linkage group (LG) 2, 26 and 29 were identified to be significantly associated with MAS resistance. Within these regions, a total of 24 genes had known functions in immunity, 10 of which were involved in NF-κB signaling pathway, suggesting the importance of NF-κB signaling pathway in MAS resistance. In addition, three suggestively significant QTL were identified on LG 11, 17, and 20. The limited numbers of QTL involved in MAS resistance suggests that marker-assisted selection may be a viable approach for catfish breeding.

Chemical Diversity and Biological Activity of African Propolis

Natural remedies have for centuries played a significant role in traditional medicine and continue to be a unique reservoir of new chemical entities in drug discovery and development research. Propolis is a natural substance, collected by bees mainly from plant resins, which has a long history of use as a folk remedy to treat a variety of ailments. The highly variable phytochemical composition of propolis is attributed to differences in plant diversity within the geographic regions from which it is collected. Despite the fact that the last five decades has seen significant advancements in the understanding of the chemistry and biological activity of propolis, a search of the literature has revealed that studies on African propolis to date are rather limited. The aim of this contribution is to report on the current body of knowledge of African propolis, with a particular emphasis on its chemistry and biological activity. As Africa is a continent with a rich flora and a vast diversity of ecosystems, there is a wide range of propolis phytochemicals that may be exploited in the development of new drug scaffolds.

Italian acacia honey exhibits lytic effects against the crayfish pathogens Aphanomyces astaci and Fusarium avenaceum

This study purpose was to evaluate the in vitro inhibitory properties of Italian acacia honey extracts against pathogenic aquatic oomycete/fungal isolates that cause different diseases in crayfish, resulting in an elevated mortality rate. The antimycotic activity of acacia honey aqueous extracts was evaluated against the strain UEF88662 of Aphanomyces astaci (oomycete) and the strain SMM2 of Fusarium avenaceum (fungus). The extracts preparation was carried out with water by a cheap, not complex and organic solvent-free procedure, with low environmental impact and the higher possibility of large-scale reproducibility. The anti-oomycete and antifungal activities were quantitatively evaluated by growth, survival and sporulation microbiological assays. The extracts displayed a dose-dependent inhibitory efficacy on oomycete and fungal growth and survival, as well as on the production of oomycete and fungal spores. Supported by future in vivo studies, our results encourage the use of natural extracts like honey as innovative tools to counteract mycotic infections. SIGNIFICANCE AND IMPACT OF THE STUDY: The continuous spread of aquatic fungal disease as the 'crayfish plague' and the 'burn spot disease' has severe ecological and commercial repercussions. Critical factor to prevent further spread is the availability of effective antifungals possibility derived from local natural resources to use in innovative strategies of control and eradication of these diseases. This study provides relevant information about the in vitro anti-oomycete and antifungal activity of Italian acacia honey aqueous extracts against two highly infectious and dangerous pathogenic species, Aphanomyces astaci and Fusarium avenaceum, that are responsible for important crayfish diseases.

A Review of Molecular Responses of Catfish to Bacterial Diseases and Abiotic Stresses

Catfish is one of the major aquaculture species in the United States. However, the catfish industry is threatened by several bacterial diseases such as enteric septicemia of catfish (ESC), columnaris disease and Aeromonas disease, as well as by abiotic stresses such as high temperature and low oxygen. Research has been conducted for several decades to understand the host responses to these diseases and abiotic stresses. With the development of sequencing technologies, and the application of genome-wide association studies in aquaculture species, significant progress has been made. This review article summarizes recent progress in understanding the molecular responses of catfish after bacterial infection and stress challenges, and in understanding of genomic and genetic basis for disease resistance and stress tolerance.

Dietary olive leaf (Olea europea L.) extract alters some immune gene expression levels and disease resistance to Yersinia ruckeri infection in rainbow trout Oncorhynchus mykiss

The aim for the present study was to investigate the effects of olive leaf (Olea europea L.) extract (OLE) on the control of Yersinia ruckeri infection in rainbow (Oncorhynchus mykiss) trout and to assess the impact on the expression of immune-related genes in the spleen and serum biochemical parameters of rainbow trout. Five experimental diets were prepared by adding 0.0%, 0.1%, 0.25%, 0.50% and 1.0% of OLE. Each diet was fed to triplicate groups of fish (mean body weight 51.22 ± 3.04 g) twice a day (at 09:00 and 17:00 h) for 60 days. The dietary supplementation of OLE did not affect growth performance and feed utilization (P > 0.05). Major changes due to graded levels of OLE in the diets were observed in blood biochemical parameters (P < 0.05). TNFα, IL1-β and IL-8 gene expressions were significanlty up-regulated in OLE 0.1% group compared with others (P < 0.05). Also, diet supplemented with OLE reduced mortality in rainbow trout fed with OLE 0.1% added diet. Present study suggests that OLE especially at 0.1% added feed may effectivelly enhance the serum biochemical parameters, survival rate and immune gene expression in rainbow trout.

Antioxidant enzymes, hematology and histology of spleen in Nile tilapia fed supplemented diet with natural extracts challenged with Aeromonas hydrophila

This study investigated the effects of dietary supplementation with the extrats of propolis and Aloe barbadensis (aloe) on the antioxydant enzime activity, hematology and histology of the spleen of Nile tilapia challenged with Aeromonas hydrophila. Seventy two juvenile Nile tilapia were divided in four treatments and three replicates and fed extract mixture for 15 days: fish fed supplemented diet with 1% of the mixture of extracts of propolis and aloe (1:1) injected with phosphate-buffered saline (PBS); fish fed suplemented diet with 1% of the mixture of extracts of propolis and aloe (1:1) injected with the A. hydrophila, fish fed supplemented diet with the mixture of propolis extracts and aloe, injected with PBS and injected with A. hydrophila. The influence of the supplementation of propolis and Aloe extracts on the immunomodulation in tilapias was observed by the evaluation of the survival of the animals after challenge with A. hydrophila. Non-supplemented fish had a 44.5% survival rate and those supplemented with 1% of the mixture of extracts showed 55.6% survival 7 days after challenge. The supplemented animals also showed a significant increase in the number of lymphocytes in the evaluation of the blood parameters and, consequently, in the histopathological evaluation, presented greater presence of centers of melanomacrophages. In addition, the activity of the antioxidant enzymes glutathione reductase (GR) in the spleen presented a significant difference in fish supplemented with 1% of the extracts mixture, being superior in the animals injected with PBS when compared to those challenged with A. hydrophila.

Ameliorative effect of propolis supplementation on alleviating bisphenol-A toxicity: Growth performance, biochemical variables, and oxidative stress biomarkers of Nile tilapia, Oreochromis niloticus (L.) fingerlings

Bisphenol-A (BPA) is one of the important pollutants in aquatic ecosystems and its detrimental effect on fish has a great concern. Propolis is a natural immune-stimulant that has various biological and pharmacological activities. Thus, its capability to alleviate the toxic effect of BPA on Nile tilapia, Oreochromis niloticus (L.) performance was assessed in a study based on a 2×2 factorial design with two levels of ethanolic extract of propolis (EEP) and two waterborne BPA concentrations in triplicates. Fish (33.9±0.55g) were exposed to 0.0 or 1.64μgBPA/L for 6weeks during which fish were fed on diets containing 0.0 or 9.0gEEP/kg diet. Fish performance, biochemical variables, and oxidative stress enzymes were significantly affected by propolis supplementation, BPA exposure, and their interaction. Propolis supplementation significantly improved fish growth and feed intake, which were significantly retarded by BPA exposure. Additionally, total protein, albumin, globulin, and acetylcholine esterase (AChE) decreased significantly. Meanwhile aspartate transferase (AST), alanine transferase (ALT), alkaline phosphatase (ALP), creatinine, and uric acid increased significantly with exposure to BPA. Levels of malondialdehyde (MDA) as well as superoxide dismutase (SOD) and catalase (CAT) activities increased significantly due to BPA exposure, whereas significant reductions in the activity of glutathione peroxidase (GPx) and glutathione S-transferase (GST) were also recorded compared to the control fish. It is noticed that EEP co-administration ameliorated these parameters. The present results evoked that propolis administration improves fish growth and alleviated BPA-induced toxicity.

Activity of Brazilian propolis against Aeromonas hydrophila and its effect on Nile tilapia growth, hematological and non-specific immune response under bacterial infection

The effect of the ethanolic extract of propolis (EEP) on Aeromonas hydrophila was analyzed by determination of minimum inhibitory concentration (MIC). Then, the effects of crude propolis powder (CPP) on growth, hemato-immune parameters of the Nile tilapia, as well as its effects on resistance to A. hydrophila challenge were investigated. The CPP (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0%) was added to the diet of 280 Nile tilapia (50.0 ± 5.7 g fish-1). Hemato-immune parameters were analyzed before and after the bacterial challenge. Red blood cell, hematocrit, hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), and hydrogen peroxide (H2O2) and nitric oxide (NO) were evaluated. The MIC of the EEP was 13% (v/v) with a bactericidal effect after 24 hours. Growth performance was significantly lower for those fish fed diets containing 2.5 and 3% of CPP compared to the control diet. Differences in CPP levels affected fish hemoglobin, neutrophils number and NO following the bacterial challenge. For others parameters no significant differences were observed. Our results show that although propolis has bactericidal properties in vitro, the addition of crude propolis powder to Nile tilapia extruded diets does not necessarily lead to an improvement of fish health.

Effects of replacing fish meal with rubber seed meal on growth, nutrient utilization, and cholesterol metabolism of tilapia (Oreochromis niloticus × O. aureus)

A feeding trial was conducted to evaluate the effects of replacing fish meal with rubber seed meal (RSM) on growth, nutrient utilization, and cholesterol metabolism of tilapia (Oreochromis niloticus × Oreochromis aureus). Five experimental diets were formulated with 0, 150, 300, 450, and 600 g kg^-1 RSM replacing graded levels of fish meal, respectively. Each diet was randomly assigned to triplicate groups of 25 fish (initial average weight 65.3 g) per aquarium in a rearing system maintained at 29 ± 1 °C for 8 weeks. Dietary 150 g kg^-1 RSM inclusion did not affect the weight gain and daily growth coefficient, whereas these were depressed by a further inclusion. Additionally, feed efficiency ratio and protein efficiency ratio were not affected by dietary RSM inclusion regardless of inclusion level. However, the inclusion of 450 and 600 g kg^-1 RSM decreased the mid-intestinal trypsin, lipase, and amylase activities; the hepatic acyl-CoA/cholesterol acyl transferase; low-density lipoprotein receptor; and 3-hydroxy-3-methyl-glutaryl-CoA reductase activities. Similarly, dietary 600 g kg^-1 RSM inclusion inhibited the plasma catalase and hepatic glutathione peroxidase activities. These results indicated that 150 g kg^-1 RSM can be included in tilapia diets, whereas higher inclusion of RSM inhibited the growth rate, digestive enzyme activity, antioxidant capacity, and cholesterol metabolism.

Protective efficacy of cationic-PLGA microspheres loaded with DNA vaccine encoding the sip gene of Streptococcus agalactiae in tilapia

Streptococcus agalactiae (S. agalactiae) is an important fish pathogen, which has received more attention in the past decade due to the increasing economic losses in the tilapia industry worldwide. As existing effective vaccines of S. agalactiae in fish have obvious disadvantage, to select immunoprotective antigens and package materials would undoubtedly contribute to the development of novel oral vaccines. In the present study, surface immunogenic protein (sip) was selected from the S. agalactiae serovar I a genomes as immunogenic protein in DNA vaccine form with cationic chitosan and biodegradable and biocompatible PLGA. The pcSip plasmid in cationic-PLGA was successfully expressed in tissues of immunized tilapia and the immunogenicity was assessed in tilapia challenge model. A significant increase was observed in the cytokine levels of IL-1β, TNF-α, CC1, CC2 in spleen and kidney tissues. Furthermore, immunized tilapia conferred different levels of protection against challenge with a lethal dose of highly virulent serovar I a S. agalactiae. Our results indicated that the pcSip plasmid in cationic-PLGA induced high level of antibodies and protection against S. agalactiae infection, could be effective oral DNA vaccine candidates.

Assessment of immune status of yellowfin seabream (Acanthopagrus latus) during short term exposure to phenanthrene

The aim of the present investigation was to assess the immune status in yellowfin seabream (Acanthopagrus latus) exposed to different concentrations of phenanthrene (Phe) for 14days. In addition, the Phe accumulation in the fish muscle was measured during the experiment. Fish were injected with different concentrations (0, 2, 20 and 40mg/kg) of Phe and samples were taken from tissue and blood of fish 1, 4, 7 and 14days after injection. Exposure of fish to Phe caused a significant decrease in white blood cells, C3 and C4 levels, lysosomal membrane stability, lysozyme activity after 4days and antibacterial activity after 7days of the experiment. In contrast, cortisol level significantly increased after 4days. The concentration of Phe in fish muscle increased rapidly after 4days. The main tissue changes observed in the head kidney including increase in melanomacrophage centers (MMCs), empty spaces between cells and hemorrhage. The degree of tissue changes ranged from normal to moderate in Phe-treated fish. The size and number of MMCs in treated fish were significantly higher than control. In conclusion, Phe toxicity in yellowfin seabream can induce increased cortisol level, tissue changes and immune suppression.

Algerian propolis extracts: Chemical composition, bactericidal activity and in vitro effects on gilthead seabream innate immune responses

Propolis has been used as a medicinal agent for centuries. The chemical composition of four propolis samples collected from four locations of the Sétif region, Algeria, using gas chromatography-mass spectrometry was determined. More than 20 compounds and from 30 to 35 compounds were identified in the aqueous and ethanolic extracts, respectively. Furthermore, the antimicrobial activity of the propolis extracts against two marine pathogenic bacteria was evaluated. Finally, the in vitro effects of propolis on gilthead seabream (Sparus aurata L.) leucocyte activities were measured. The bactericidal activity of ethanolic extracts was very high against Shewanella putrefaciens, average against Photobacterium damselae and very low against Vibrio harveyi. The lowest bactericidal activity was always that found for the aqueous extracts. When the viability of gilthead seabream head-kidney leucocytes was measured after 30 min' incubation with the different extracts, both the ethanolic and aqueous extracts of one of the propolis samples (from Babor) and the aqueous extract of another (from Ain-Abbassa) provoked a significant decrease in cell viability when used at concentrations of 100 and 200 μg ml^-1. Furthermore, significant inhibitory effects were recorded on leucocyte respiratory burst activity when isolated leucocytes where preincubated with the extracts. This effect was dose-dependent in all cases except when extracts from a third propolis sample (from Boutaleb) were used. Our findings suggest that some of Algerian propolis extracts have bactericidal activity against important bacterial pathogens in seabream and significantly modulate in vitro leucocyte activities, confirming their potential as a source of new natural biocides and/or immunomodulators in aquaculture practice.

Enhancing growth and non-specific immunity of grass carp and Nile tilapia by incorporating Chinese herbs (Astragalus membranaceus and Lycium barbarum) into food waste based pellets

The effects of Astragalus membranaceus and Lycium barbarum on the growth performance and non-specific immunity of grass carp and Nile tilapia were studied. Herb extracts of Chinese medicinal herbs (2 g kg^-1 or 20 g kg^-1) were incorporated into food waste based fish feed pellets. Fish growth and selected non-specific immune parameters of grass carp and Nile tilapia were studied in two separate feeding trials. Both grass carp and Nile tilapia fed diets of feed pellets containing 2 g kg^-1Lycium barbarum extract achieved the best relative weight gain, feed conversion ratio, specific growth rate and protein efficiency ratio among all experimental diets. Fish fed with diets containing 2 g kg^-1Lycium barbarum also resulted in significantly higher total immunoglobin, bactericidal activity and anti-protease activity; and also a lower mortality when challenged with pathogenic bacteria. On the other hand, both fish species fed with diets containing 20 g kg^-1 of Astragalus membranaceus and 20 g kg^-1Lycium barbarum, resulted in significantly impaired weight gain. In addition, incorporation of 2 g kg^-1Lycium barbarum extract would be a more suitable dose for both fish species, in terms of achieving better feed conversion ratio, specific growth rate, protein digestibility, and improved non-specific immune parameters. Based on this study, it can be concluded that waste based feed pellets incorporated with Chinese medicinal herb extracts have the ability to enhance growth and immunity of fish. Therefore, the use of Chinese medicinal herbs in aquaculture should be encouraged, in order to replace certain antibiotics known to impose environmental and health effects through the discharge of aquaculture effluents.

Oreochromis mossambicus diet supplementation with Psidium guajava leaf extracts enhance growth, immune, antioxidant response and resistance to Aeromonas hydrophila

In this research, we focused on the efficacy of aqueous and ethanol leaf extracts of Psidium guajava L. (guava) based experimental diets on the growth, immune, antioxidant and disease resistance of tilapia, Oreochromis mossambicus following challenge with Aeromonas hydrophila. The experimental diets were prepared by mixing powdered (1, 5 and 10 mg/g) aqueous and ethanol extract of guava leaf with commercial diet. The growth (FW, FCR and SGR), non-specific cellular immune (myeloperoxidase activity, reactive oxygen activity and reactive nitrogen activity) humoral immune (complement activity, antiprotease, alkaline phosphatase activity and lysozyme activity) and antioxidant enzyme responses (SOD, GPX, and CAT) were examined after 30 days of post-feeding. A significant enhancement in the biochemical and immunological parameters of fish were observed fed with experimental diets compared to control. The dietary supplementation of P. guajava leaf extract powder for 30 days significantly reduced the mortality and increased the disease resistance of O. mossambicus following challenge with A. hydrophila at 50 μl (1 × 10⁷ cells ml^-1) compared to control after post-infection. The results suggest that the guava leaf extract could be used as a promising feed additive in aquaculture.

Camellia sinensis supplemented diet enhances the innate non-specific responses, haematological parameters and growth performance in Mugil cephalus against Photobacterium damselae

This study evaluated the effect of dietary supplementation of Camellia sinensis leaf-extract on non-specific immune responses and disease resistance of Mugil cephalus fingerling against P. damselae. Fish were fed with 0 (unsupplemented), 50, 100 and 200 mg/kg of green tea extract (GTE) supplemented diets. Results indicated that GTE decreased mortality in M. cephalus in a dose-dependent manner after challenge with P. damselae. Haematological parameters containing RBC, Hct, Hb and WBC and growth performance (weight gain) showed remarkable changes in comparison with control group. In addition, the phagocytic (PA) and respiratory burst activity (RBA) significantly increased in M. cephalus, fed 100 and 50, 100 and 200 mg/kg GTE, respectively. Lysozyme statistically increased in GTE supplemented fish. Overall, our results indicated that incorporation of C. sinensis supplemented diet at 100 and 200 mg/kg doses significantly enhanced the immune responses in M. cephalus and that the mortality percentage could be remarkably reduced after challenging the fish against P. damselae.

The response of fish to immunostimulant diets

In order to maintain fish health and to improve performance immunostimulants have been used as dietary additives to improve weight gain, feed efficiency, and/or disease resistance in cultured fish. In aquaculture, non-specific immunostimulants have been widely used probably due to the limited knowledge of the immune response in fish and the ease of their application. Many studies have been carried out to assess the effect of dietary immunostimulants in fish including algal derivatives, herb and plant extract containing diets using a wide range of downstream analytical techniques. Many immunostimulants are based upon tradition and folklore transferred through generations and specific to certain geographical regions rather than known biological properties. However, there are studies in which it is possible to observe a clear and direct dose-dependent stimulatory effect upon the immune system. Other dietary supplements used contain PAMPs (Pathogen Associated Molecular Patterns) as immunostimulants whose recognition depends upon PRR (pathogen recognition receptor) interactions including the TLRs (Toll-like receptor). Despite the growing interest in the use of immunostimulants across the aquaculture industry the underlying mechanisms of ligand recognition, extract composition and activation of the fish immune response remains fragmented. In this review we focus upon the last 15 years of studies addressing the assessment of: (1) plant, herb and algae extracts; and (2) PAMPs, upon non-specific immune parameters of activation and immunostimulant diet efficacy.

Honey bee pollen improves growth, immunity and protection of Nile tilapia (Oreochromis niloticus) against infection with Aeromonas hydrophila

The mode of action of honey bee pollen (HBP) was investigated in Nile tilapia (Oreochromis niloticus) challenged with Aeromonas hydrophila. Thus, fish with an average weight of 29 ± 3 g were divided into four groups, and fed with HBP-free diet (control), and 1%, 2.5% and 4% (w/v) HBP incorporated into basal diet for 10, 20 and 30 days. Immunological, hematological, biochemical and growth parameters were measured, and sub-groups of fish were challenged with A. hydrophila via intraperitoneal injection. HBP significantly increased the growth performance parameters [body weight, length, average daily gain (ADG), specific growth rate (SGR), and feed efficiency ratio (FER)] and immunological (phagocytic activity, serum bactericidal activity and nitroblue tetrazolium assay (NBT)), hematological (hematocrit (Hct), leucocrit (Lct), the numbers of neutrophils, monocytes and lymphocytes) and biochemical parameters (serum total protein, albumin and globulin ratios). Furthermore, all treated fish exhibited significant protection against challenge with A. hydrophila, with the highest protection (93%) observed in the group fed with 2.5% (w/v) HBP for 20 and 30 days.

Serum bactericidal activity as indicator of innate immunity in pacu Piaractus mesopotamicus (Holmberg, 1887)

The immune system of teleost fish has mechanisms responsible for the defense against bacteria through protective proteins in several tissues. The protein action can be evaluated by serum bactericidal activity and this is an important tool to analyze the immune system. Pacu, Piaractus mesopotamicus, is one of the most important fish in national aquaculture. However there is a lack of studies on its immune responses. In order to standardize and assess the accuracy of the serum bactericidal activity assay, fish were briefly challenged with Aeromonas hydrophila and sampled one week after the challenge. The bacterial infection increased the concentration of protective proteins, resulting in a decrease of colony-forming unit values expressed as well as an enhanced serum bactericidal activity. The protocol showed a reliable assay, appropriate to determine the serum bactericidal activity of pacu in the present experimental conditions.

Comparative transcriptional analysis reveals distinct expression patterns of channel catfish genes after the first infection and re-infection with Aeromonas hydrophila

To determine whether transcriptional levels of channel catfish (Ictalurus punctatus) genes are differentially regulated between a first infection with Aeromonas hydrophila and a re-infection, suppression subtractive hybridization (SSH) was performed in this study using anterior kidney cDNA after the re-infection as tester. Of the 96 clones isolated from the SSH library, 28 unique expressed sequence tags (ESTs) were obtained, of which eight were confirmed to be slightly but significantly (P < 0.05) more up-regulated by the re-infection at 6 h post infection (hpi). Expression kinetics studies at 3, 6, 12, 24, and 48 hpi revealed that the eight ESTs were significantly (P = 0.016) more up-regulated by the first infection, with a major peak at 3 hpi. A total of 96 genes reported in literature to be up-regulated by bacterial infections were selected and subjected to expression analysis at 3 hpi. Of the 96 selected genes, 19 were found to be significantly (P < 0.05) induced by A. hydrophila after the first infection and the re-infection. The 19 genes belonged to the following five main categories: 1) toll-like receptor (TLR2, TLR3, TLR5, TLR21); 2) antimicrobial peptide (NK-lysin type 1, NK-lysin type 2, NK-lysin type 3, cathepsin D, transferrin, hepcidin); 3) cytokine or chemokine (interleukin-1β, interleukin-10, tumor necrosis factor α, chemokine CXCL-10); 4) signaling proteins (cadherin EGF LAG seven-pass G-type receptor 1, very large inducible GTPase 1, arginine deiminase type 2, lymphokine-activated killer T-cell originated protein kinase); 5) lysozyme (lysozyme c). Overall, the total 27 genes (8 ESTs plus the 19 selected genes) were significantly (P < 0.001) more induced by the first infection. Peaked expression of lysozyme c and serum lysozyme activity after the first infection were seen at 24 hpi, whereas that after the re-infection were seen at 12 hpi, suggesting that both innate and adaptive immunity were involved in the defense against the re-infection of A. hydrophila.

Effect of Sophora flavescens on non-specific immune response of tilapia (GIFT Oreochromis niloticus) and disease resistance against Streptococcus agalactiae

The paper describes the effect of a diet supplemented with the Chinese traditional herbal medicine Sophora flavescens on the immunity and disease resistance of an Oreochromis niloticus GIFT strain. Experimental diets containing 0.025%, 0.050%, 0.100%, 0.200%, and 0.400% S. flavescens, as well as a control group without S. flavescens were used. We tested the non-specific humoral immune responses (lysozyme, antiprotease, and complement) and cellular immune responses (reactive oxygen species and nitrogen species production and myeloperoxidase), as well as disease resistance against Streptococcus agalactiae. S. flavescens supplementation at all dose significantly enhanced serum lysozyme, antiprotease, and natural hemolytic complement activity. Similarly, all S. flavescens doses enhanced cellular myeloperoxidase activity. The increased production of reactive oxygen species and reactive nitrogen intermediates by peripheral blood leucocytes was observed in most of the treatment groups throughout the test period. The fish fed 0.100% S. flavescens had a percent mortality of 21.1% and a relative percent survival of 73.3% compared with the group fed the basal diet during the S. agalactiae challenge. The results suggest that S. flavescens can be recommended as a tilapia feed supplement to enhance fish immunity and disease resistance against S. agalactiae.

Attenuation of a virulent Aeromonas hydrophila with novobiocin and pathogenic characterization of the novobiocin-resistant strain

AIM

To determine whether novobiocin resistance strategy could be used to attenuate a virulent Aeromonas hydrophila AH11P strain and to characterize the growth and pathogenic differences between the novobiocin-resistant strain and its virulent parent strain AH11P.

METHODS AND RESULTS

A novobiocin-resistant strain AH11NOVO was obtained from a virulent Aer. hydrophila strain AH11P through selection of resistance to novobiocin. AH11NOVO was found to be avirulent to channel catfish (Ictalurus punctatus), whereas AH11P was virulent. When AH11NOVO vaccinated channel catfish were challenged with AH11P at 14 days postvaccination, relative per cent of survival of vaccinated fish was 100%. The cell proliferation rate of AH11NOVO was found to be significantly (P < 0.05) less than that of AH11P. In vitro motility assay revealed that AH11NOVO was nonmotile, whereas AH11P was motile. AH11NOVO had significantly (P < 0.05) lower in vitro chemotactic response to catfish mucus than that of AH11P. Although the ability of AH11NOVO to attach catfish gill cells was similar to that of AH11P, the ability of AH11NOVO to invade catfish gill cells was significantly (P < 0.05) lower than that of AH11P.

CONCLUSIONS

The novobiocin-resistant AH11NOVO is attenuated and different from its parent AH11P in pathogenicity.

SIGNIFICANCE AND IMPACT OF THE STUDY

The significantly lower chemotactic response and invasion ability of AH11NOVO compared with that of its virulent parent strain AH11P might shed light on the pathogenesis of Aer. hydrophila.

The effect of mistletoe, Viscum album coloratum, extract on innate immune response of Nile tilapia (Oreochromis niloticus)

The purpose of the present study was to evaluate the effect of dietary mistletoe extracts on non-specific immune response and disease resistance of Nile tilapia (Oreochromis niloticus) against Aeromonas hydrophila infection. Tilapia fingerlings were fed with a diet containing 0 mg as a control, 10 mg, 50 mg, and 200 mg mistletoe powder kg(-1) dry diet for 80 days. The immunological parameters, respiratory burst activity, lysozyme activity, alternative complement haemolysis activity (ACH(50)), and phagocytic activity of fish were investigated following 20, 40 and 80 days of feeding. Fish were challenged with A. hydrophila on 80 days after feeding and mortalities were checked over 10 days post-infection. The results show that fish fed with mistletoe extract exhibited an increase in activity in all immunological parameters (P < 0.05) compared to the control group depending on feeding periods and doses of mistletoe. Following challenge with A. hydrophila, 42% less survivability was observed in the control group than in other experimental diet groups. The highest survival rate (83%) was shown in the group fed with a 50 mg mistletoe kg(-1) diet. The results suggest that mistletoe enables tilapia to promote immunity and be more resistant to A. hydrophila infection.

Atividade antimicrobiana in vitro de extratos etanólicos de própolis de três estados brasileiros sobre Aeromonas hydrophila isoladas de peixes

O presente estudo teve como objetivo avaliar a sensibilidade in vitro de Aeromonas hydrophila frente a extratos etanólicos de própolis (uma verde e duas marrons) obtidos em três estados brasileiros (Minas Gerais, Ceará e Pernambuco). Para verificar a atividade antimicrobiana in vitro da própolis, 15 isolados de A. hydrophila foram testados para determinar a Concentração Bactericida Mínima (CBM) dos extratos. Curvas de sobrevivência para o crescimento bacteriano foram determinadas pela incubação dos isolados em extratos etanólicos de própolis a 15% por 24 horas. As médias da CBM dos extratos de própolis foram 1,68% para a própolis verde, 2,31% para a própolis marrom do Ceará e 3,75% para a própolis marrom de Pernambuco. A curva de sobrevivência dos isolados demonstrou uma inibição parcial com até três horas de incubação. Este resultado é compatível com o efeito bacteriostático da própolis, o que pode ser de interesse para a terapia em aquicultura, como alternativa às poucas drogas antimicrobianas disponíveis.

Transcriptional profiles of multiple genes in the anterior kidney of channel catfish vaccinated with an attenuated Aeromonas hydrophila

A total of 22 uniquely expressed sequence tags (ESTs) were identified from channel catfish anterior kidney subtractive cDNA library at 12 h post vaccination with an attenuated Aeromonas hydrophila (AL09-71 N+R). Of the 22 ESTs, six were confirmed to be significantly (P < 0.05) induced by the vaccination. Of 88 channel catfish genes selected from literature, 14 were found to be significantly (P < 0.05) upregulated by the vaccination. The transcriptional levels of the total 20 genes induced by the vaccination were then compared to that induced by the virulent parent A. hydrophila (AL09-71) at different time points. At 3 h post vaccination (hpv) or infection (hpi), Na(+)/K(+) ATPase α subunit was upregulated the most. At 6 and 12 hpv or hpi, hepcidin and interleukin-1β were induced the highest. At 24 hpv or hpi, hepcidin was upregulated the most, followed by lysozyme c. At 48 hpi, lysozyme c and hepcidin were significantly induced. When vaccinated fish were challenged by AL09-71, relative percent of survival of vaccinated fish were 100% at 14 days post vaccination (dpv). Transcriptional levels of toll-like receptor 5 and hepcidin were significantly upregulated in vaccinated fish at 14 dpv. Taken together, our results suggest that vaccination with attenuated A. hydrophila mimics infection by live bacteria, inducing multiple immune genes in channel catfish.

Effect of ethanolic extract of propolis on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss)

This study was conducted to evaluate the effect of ethanolic extract of propolis (EEP) on growth performance and plasma biochemical parameters of rainbow trout (Oncorhynchus mykiss). Graded levels of EEP [0 (control), 1, 2, and 4 g kg(-1) diet] were fed to trout juveniles (mean weight 7.73 ± 0.17 g) for 10 weeks. Dietary EEP supplementation regardless of inclusion level significantly improved the specific growth rate of fish. Similarly, supplemental EEP generally improved the feed efficiency ratio and protein efficiency ratio, but no significant differences were observed between the 1 g kg(-1) EEP group and the control group. In addition, dietary EEP supplementation generally increased the plasma superoxide dismutase, lysozyme, total antioxidant capacity, glutathione peroxidase, and catalase activities, but decreased the plasma malondialdehyde level. The plasma triglycerides level was significantly lower in the 1 or 4 g kg(-1) EEP group as compared with the control group. Dietary EEP supplementation generally decreased the plasma aspartate aminotransferase and alanine aminotransferase activities, but increased the hepatic aspartate aminotransferase and alanine aminotransferase activities. These results indicate the potential to use the EEP as a growth promoter, hepatoprotective agent, and immunostimulant for rainbow trout.

Identification and expression profiles of multiple genes in Nile tilapia in response to bacterial infections

To understand the molecular mechanisms involved in response of Nile tilapia (Oreochromis niloticus) to bacterial infection, suppression subtractive cDNA hybridization technique was used to identify upregulated genes in the posterior kidney of Nile tilapia at 6h post infection with Aeromonas hydrophila. A total of 31 unique expressed sequence tags (ESTs) were identified from 192 clones of the subtractive cDNA library. Quantitative PCR revealed that nine of the 31 ESTs were significantly (p<0.05) upregulated in Nile tilapia at 6h post infection with A. hydrophila at an injection dose of 10(5)CFU per fish (≈ 20% mortality). Of the nine upregulated genes, four were also significantly (p<0.05) induced in Nile tilapia at 6h post infection with A. hydrophila at an injection dose of 10(6)CFU per fish (≈ 60% mortality). Of the four genes induced by A. hydrophila at both injection doses, three were also significantly (p<0.05) upregulated in Nile tilapia at 6h post infection with Streptococcus iniae at doses of 10(6) and at 10(5)CFU per fish (≈ 70% and ≈ 30% mortality, respectively). The three genes induced by both bacteria included EST 2A05 (similar to adenylate kinase domain containing protein 1), EST 2G11 (unknown protein, shared similarity with Salmo salar IgH locus B genomic sequence with e value of 0.02), and EST 2H04 (unknown protein). Significant upregulation of these genes in Nile tilapia following bacterial infections suggested that they might play important roles in host response to infections of A. hydrophila and S. iniae.

Virulence of Aeromonas hydrophila to channel catfish Ictaluras punctatus fingerlings in the presence and absence of bacterial extracellular products

We investigated the virulence of three 2009 west Alabama isolates of Aeromonas hydrophila (AL09-71, AL09-72 and AL09-73) to channel catfish Ictalurus punctatus fingerlings (4.6 +/- 1.3 g) in the presence and absence of extracellular products (ECPs) from overnight bacterial culture using both bath immersion and intraperitoneal injection routes. At a concentration of 1.65 x 10(8) colony-forming units (CFU) ml(-1), AL09-73 without its ECPs killed 100% of the catfish fingerlings within 2 h by bath immersion. However, at a similar concentration, AL09-73 in the presence of its ECPs killed only 23 +/- 6% catfish fingerlings. The absence of ECPs in the bath immersion experiment also significantly (p < 0.05) increased the virulence of AL09-71, AL09-72, and AL98-C1B, a 1998 Alabama strain of A. hydrophila, suggesting that the virulence of the 4 A. hydrophila isolates was mainly due to bacterial cells, not to their overnight ECPs. Filter-sterilized ECPs failed to kill any catfish by bath immersion or injection. The virulence order of the 4 A. hydrophila isolates, by both bath immersion and intraperitoneal injection, was: AL09-73 > or = AL09-71 > AL09-72 > or = AL98-C1B. At 2 h post bath immersion, all 4 isolates of A. hydrophila were found in all tissues studied (skin, intestine, liver, spleen, kidney, gill and brain), with the highest bacteria count being in the gill and kidney.

Molecular identification and virulence of three Aeromonas hydrophila isolates cultured from infected channel catfish during a disease outbreak in west Alabama (USA) in 2009

Three isolates (AL09-71, AL09-72, and AL09-73) of Aeromonas hydrophila were cultured from infected channel catfish Ictalurus punctatus during a disease outbreak in west Alabama, USA, in August 2009. Sequence analysis of the 16S-23S rDNA intergenic spacer region (ISR), cpn60, gyrB, and rpoD genes of the 3 strains revealed that the 3 strains were closely related to each other, sharing 97 to 99% nucleotide sequence similarities. However, ISR sequences of the 3 isolates from 2009 shared only 64% nucleotide sequences with AL98-C1B, a 1998 isolate of A. hydrophila cultured from diseased fish in Alabama. Sequences of cpn60, gyrB, and rpoD from the 3 isolates from 2009 shared 91 to 95% homologies with AL98-C1B. Based on both LD50 and LD95 values of intraperitoneal injection assays, the virulences of the 3 isolates from 2009 were not significantly different from each other, but were at least 200-fold more virulent than AL98-C1B, indicating that the 3 west Alabama isolates of A. hydrophila from 2009 were highly virulent to channel catfish.

An in vitro screening method to evaluate chemicals as potential chemotherapeutants to control Aeromonas hydrophila infection in channel catfish

AIMS

To develop an in vitro screening method to be used for identifying potential effective chemotherapeutants to control Aeromonas hydrophila infections.

METHODS AND RESULTS

Using catfish gill cells G1B and four chemicals (hydrogen peroxide, sodium chloride, potassium permanganate and D-mannose), the feasibility of using an in vitro screening method to identify potential effective chemotherapeutants was evaluated in this study. In vitro screening results revealed that, at concentration of 100 mg l⁻¹, H₂O₂ was the only chemical tested that was able to completely abolish the attachment and invasion of Aer. hydrophila to catfish gill cells. In vivo virulence studies using live channel catfish through bath immersion confirmed that H₂O₂ was the only chemical tested that was able to significantly (P < 0·001) reduce the mortality (from 90 or 100% to 0 or 20%) caused by Aer. hydrophila infections.

CONCLUSIONS

The in vitro screening method using catfish gill cells G1B could be used to initially identify potential effective chemotherapeutants to control Aer. hydrophila.

SIGNIFICANCE AND IMPACT OF THE STUDY

An in vitro screening method using catfish gill cells to identify potential effective chemotherapeutants described here will cut cost in research compared with the method of using live fish to screen lead compounds for fish disease control.

Long-term effects of propolis on serum biochemical parameters of rainbow trout (Oncorhynchus mykiss)

Long-term effects of propolis administration on serum biochemical parameters of rainbow trout (Oncorhynchus mykiss) were investigated. To determine the possible toxicity and side effects of propolis, fish were fed on diets containing 0, 0.5, 1.5, 4.5 and 9 g propolis/kg diet for 8 weeks. At the end of the experiment, various seric biochemical parameters were determined. Our results showed that all dosages induced no significant alterations in growth parameters and the seric levels of total protein, albumin, globulin, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol and triglycerides and activities of glutamic pyruvic transaminase, glutamic oxaloacetic transaminase, alkaline phosphatase and lactate dehydrogenase, when compared to the control group. On the basis of our findings, propolis is a non-toxic substance for rainbow trout and its long-term administration might not have any side effects.