Immune-related gene expression and physiological responses in rainbow trout (Oncorhynchus mykiss) after intraperitoneal administration of Rhodomyrtus tomentosa leaf extract: A potent phytoimmunostimulant

Dietary flaxseed (Linum usitatissimum) oil supplementation affects growth, oxidative stress, immune response, and diseases resistance in rainbow trout (Oncorhynchusmykiss)

This paper describes the effects of flaxseed (Linum usitatissimum) oil (FSO) as a feed additive on growth performance, oxidative stress, immunity, and disease resistance in rainbow trout (Oncorhynchus mykiss). Four-hundred-and-twenty rainbow trout individuals (mean weight: 25.66 ± 1.33 g) were fed with different doses of FSO (0.5, 1, and 1.5%) ad libitum two times a day for 9 weeks. At the end of the feeding, growth performance was evaluated and the fish were challenged with two different bacteria (Yersinia ruckeri and Aeromonas hydrophila). At the end of the 3rd, 6th, and 9th weeks, blood and tissue samples were collected from 9 fish per treatment to evaluate innate immune response, cytokine gene expression levels, antioxidant enzyme activities and lipid peroxidation levels, and digestive enzyme activities. Determination of haematological parameters and histological examination was also carried out to evaluate the general health status of the fish. Results showed that the final weight and specific growth rate of fish supplemented with FSO increased significantly (p < 0.05). FSO-supplemented fish showed higher resistance to Y. ruckeri infection than the control group (p < 0.05). However, survival rates of all groups in A. hydrophila challenge test were similar (p > 0.05). Among the investigated innate immune response parameters, the potential killing activity of phagocytes, myeloperoxidase activity, and lysozyme activity increased in the FSO-supplemented groups (p < 0.05). Almost all cytokine gene expression levels in the experimental groups up-regulated especially after 9 weeks of feeding in the head kidney and intestine (p < 0.05). Similarly, superoxide dismutase and catalase activities were found to be significantly higher in the FSO group than in the control (p < 0.05) whereas, the lipid peroxidation levels drastically declined as a result of the FSO supplementation (p < 0.05). These results suggest that FSO can improve growth, enhance immune response, and lower oxidative damage in rainbow trout when supplemented at the rates of 0.5-1.5% for 9 weeks.

Effects of white mustard (Sinapis alba) oil on growth performance, immune response, blood parameters, digestive and antioxidant enzyme activities in rainbow trout (Oncorhynchusmykiss)

A study was conducted to evaluate the effects of dietary supplementation of white mustard (Sinapis alba) oil (WMO) on growth performance, immune responses, digestive and antioxidant enzyme activities in juvenile rainbow trout (Oncorhynchus mykiss). For this purpose, fish (initial weight: 25.77 ± 0.13 g) were divided into four experimental groups in triplicate and fed ad libitum twice a day with diets containing WMO at 0 (control), 0.5, 1, and 1.5% of diet for 9 weeks. Three fish from each tank (n:9 per treatment) were sampled on 21st, 42nd, and 63rd days for further analyses. At the end of the feeding period, fish were challenged with Aeromonas hydrophila and Yersinia ruckeri in two separate experimental setups. Results showed that final weight, weight gain, and specific growth rate were significantly increased in all experimental groups compared to the control. Feed conversion ratio was similar among treatments. Respiratory burst and potential killing activity decreased in all experimental groups compared to the control (P < 0.05). Lysozyme and myeloperoxidase activities were elevated in all experimental groups at the end of the experiment compared to the control (P < 0.05). Cytokine gene expressions in the head kidney and intestine were elevated in all experimental groups compared to that of the control in general (P < 0.05). Hematological responses of the experimental fish groups were similar to that of the control (P > 0.05). Pepsin and trypsin levels decreased in all experimental groups (P < 0.05). In terms of antioxidant enzyme activities, significant improvement in liver superoxide dismutase, catalase, and glutathione s-transferase activities in all treatment groups were determined (P < 0.05). In addition, a significant decline in liver lipid peroxidation levels was recorded in all treated groups at all sampling times compared to the control (P < 0.05). At the end of this feeding trial, no significant differences (P > 0.05) were observed in survival against A. hydrophila among experimental groups compared to the control (P > 0.05). However, increased survival against Y. ruckeri was determined in experimental fish groups (P < 0.05). This study suggests that white mustard oil had a favorable effect on the overall health and growth of rainbow trout.

Environmentally relevant concentrations of fenvalerate induces immunotoxicity and reduces pathogen resistance in Chinese rare minnow (Gobiocypris rarus)

Fenvalerate is a broadly used type II pyrethroid with a potential toxic effect in fish. However, information on the immunotoxicity of fenvalerate in fish is scarce. Here, to discover the immunotoxicity of fenvalerate and its underlying mechanism in fish, adult Chinese rare minnow was exposed to fenvalerate at 0, 0.3, 1, and 3 μg/L for 28 days and then subjected to Pseudomonas fluorescens (P. fluorescens) challenge. Fenvalerate induced significant pathological changes, with disintegration of cell boundaries in the intestine, epithelial hyperplasia in gills, and vacuolation of hepatocytes at 3 μg/L treatment. Additionally, the pathological characteristics were more serious during P. fluorescens infection after fenvalerate exposure. A significant increase in neutrophil counts was observed after 3 μg/L fenvalerate exposure for 28 days (p < 0.05), whereas significantly increased monocyte and neutrophil counts and greatly decreased lymphocyte counts were detected at 24 h post-injection (hpi) with P. fluorescens (p < 0.05). Furthermore, obvious decreases in LYS, IgM, ALP, and C3 levels were detected in plasma after 3 μg/L fenvalerate exposure for 28 days, which was consistent with the results at 24 and 48 hpi. Notably, fish exposed to fenvalerate suppressed the transcription of TLR-NF-κB signaling pathway-relevant genes in response to P. fluorescens, accompanied by high mortalities and bacterial loads. Therefore, our results demonstrate that fenvalerate at environmentally relevant concentrations caused immunotoxicity in fish. This study highlights the importance of considering the combined effects of chemicals and pathogens to refine our ability to predict the effects of environmental contaminants on aquatic organisms.

Growth hormone secretagogue peptide-6 enhances oreochromicins transcription and antimicrobial activity in tilapia (Oreochromis sp.)

Growth Hormone-Releasing Peptide 6 (GHRP-6) (His-(D-Trp)-Ala-Trp-(D-Phe)-Lys-NH2) is an agonist of the growth hormone secretagogue receptor. GHRP-6 mimics the effect of ghrelin. The present study focuses on the immunomodulatory effects of GHRP-6 in tilapia with and without the presence of Pseudomonas aeruginosa infection. GHRP-6 up-regulated the transcription levels of three piscidin-like antimicrobial peptides (Oreochromicins I, II, and III) and granzyme in a tissue-dependent manner. Antimicrobial activity stimulation in serum (lysozyme and anti-protease activity) was also confirmed. Besides, GHRP-6 enhanced the in vitro antimicrobial activity against P. aeruginosa in tilapia gills mucus and serum samples and decreased the bacterial load in vivo after infection with this Gram-negative bacterium. Our results evidenced, for the first time, a direct link between a growth hormone secretagogue ghrelin mimetic in fish and the enhancement of antimicrobial peptides transcription, which suggests that this secretagogue is capable to lead the activation of microbicidal activity in tilapia. Thus, these results open new possibilities for GHRP-6 application in aquaculture to stimulate the teleost immune system as an alternative treatment against opportunistic bacteria.

Dietary Ginkgo biloba leaf extract alters immune-related gene expression and disease resistance to Aeromonas hydrophila in common carp Cyprinus carpio

Ginkgo biloba leaf is widely used in traditional medicine in China. The present study aimed to illustrate the effects of dietary Ginkgo biloba leaf extract (GBLE) on growth performance and immune responses in common carp infected by Aeromonas hydrophila. Six different diets either not treated (control) or treated with 0.5, 1, 2, 5 and 10 g/kg of GBLE were designed to feed the fishes for 8 weeks. The results indicated that, compared to the control groups, 10 g/kg dietary GBLE significantly increased body growth and feed utilization. In GBLE dietary groups, red blood cell levels, white blood cells, hematocrit, hemoglobin, total protein, albumin and globulin were significantly increased relative to the control groups. Dietary supplementation with 5 g/kg GBLE increased the phagocytic ratio, and phagocytic indexes increased in the 2, 5 and 10 g/kg groups relative to the control groups. Moreover, 2, 5 and 10 g/kg GBLE diets increased O₂^- production compared to the control groups. Additionally, GBLE diets stimulated lysozyme activity (in 10 g/kg group) and inhibited bactericidal activity (in 0.5, 2, 5 and 10 g/kg group). Quantitative real-time PCR showed that IL1β, IL8, TNF-α, IL10, TGFβ, and inducible enzyme genes were prone to decrease while SAA, hepcidin and GPX1 were increased due to the GBLE diet in the intestine. In the head-kidney, the GBLE treatment decreased IL1β, IL8, TNF-α, IL10, TGFβ, INOS and arginase gene expressions, whereas SOD upregulation was found in the GBLE condition. The mRNA expressions of IL1β, IL8, TNF-α, IL10 and INOS were decreased, but SAA, hepcidin, GPX1 and SOD mRNA levels were increased in the spleen in the GBLE diet compared to the control. Additionally, diet supplemented with GBLE improved the survival rate infected with A. hydrophila. Our observations suggest that GBLE effectively enhanced growth performance, modulated immune-related gene expression. It improved survival rate of common carp after A. hydrophila infection and the optimum concentration we recommend is 10 g/kg of GBLE.

Modulation of posterior intestinal mucosal proteome in rainbow trout (Oncorhynchus mykiss) after Yersinia ruckeri infection

Yersinia ruckeri is the causative agent of enteric redmouth disease in salmonids. In fish, the intestine represents an important site of nutrient uptake, host–pathogen interactions, and defense. The posterior intestine can be inflamed, reddened, and filled with an opaque, yellowish fluid during Y. ruckeri infection. Herein, we report an investigation on the proteome alteration in the posterior intestinal mucosa of rainbow trout (Oncorhynchus mykiss) after exposure to Y. ruckeri. The intestinal mucosal proteins were identified and quantified by a shotgun proteomic approach by applying data-independent quantification with sequential windowed acquisition of all theoretical mass spectra (SWATH). A total of 437 proteins were found to be differentially up- or downregulated in the posterior intestine. Gene ontology of upregulated proteins pointed to their involvement into exopeptidase, endopeptidase, and hydrolase activities, while the downregulated proteins were involved in lipid metabolism, actin binding, and translation processes. Additionally, upregulated proteins were predicted to be involved in lysosome, oxidative phosphorylation, and metabolic pathways, while downregulated proteins were implicated in focal adhesion, regulation of actin cytoskeleton, protein digestion and absorption pathways. This study showed that Y. ruckeri infection can alter protein abundance involved in serine-type carboxypeptidase, cysteine and aspartic-type endopeptidases, metallopeptidases, antioxidant defense, calcium ion binding, glycolytic and carbohydrate metabolic processes in the proteome of the intestinal mucosa of rainbow trout.

Immunomodulatory effects of orally administrated florfenicol in rainbow trout (Oncorhynchus mykiss) following experimental challenge with streptococcosis/lactococcosis

The purpose of the present work was to determine whether florfenicol (FFC) as the prominent broad-spectrum antibiotic could affect serum biochemical and immunological parameters, as well as immune-related genes expression in rainbow trout (55 ± 7.6 g) challenged with the Lactococcus garvieae and Streptococcus iniae. In the first trial, the doses of the pathogens for challenge test were determined based on LD50. The therapeutic dosage of the drug (15 mg.kg^-1 BW for 10 consecutive days) was administrated as medicated feed. After anesthesia, blood and kidney samples were collected from individual fish and were kept in deep freezing mode until the beginning of the measurements. Serum biochemical and enzymatic indices were measured using commercial kits. Immune parameters including total immunoglobulin level, lysozyme, ACH50, respiratory burst (RB), and phagocytic activities (PA) and the expression of immune genes namely TNF-α, IL-1β, IL-8, and IgM was evaluated. The levels of lysozyme and RB activities, as well as the expression of TNF-α and IL-1β genes, showed a significant increase in the FFC treated/infected fish compared to untreated diseased fish (P < 0.05). In contrast, serum total immunoglobulin and IgM-related genes expression were suppressed following drug administration represented by a significant reduction in untreated streptococcal infected fish compared to other treatments (P < 0.05). However, no significant effect of FFC was observed on serum ACH50 activity, PA values and IL-8-related gene expression (P > 0.05). These results demonstrated that FFC treatment could improve some physiological status including stress resistance and some liver function parameters, and much innate immunity was invigorated, but at the same time, the suppressive effects of FFC on acquainted immunity cannot be ignored.

Evaluation of development, locomotor behavior, oxidative stress, immune responses and apoptosis in developing zebrafish (Danio rerio) exposed to TBECH (tetrabromoethylcyclohexane)

Tetrabromoethylcyclohexane (TBECH), as one emerging brominated flame retardants, is ubiquitous in the environment, including water and aquatic organisms. TBECH was found to exhibit endocrine-disrupting effects in different models, whereas a survey of comprehensive toxic effects of TBECH on zebrafish is limited. In the present study, zebrafish (Danio rerio) were waterborne exposed continuously to TBECH from embryonic stage (3 h post-fertilization (hpf)) to the time when the respective parameters were evaluated. Exposure to TBECH reduced hatchability of zebrafish embryos at 72 and 96 hpf, diminished heart rate of zebrafish larvae at 48 hpf, and increased malformation in zebrafish larvae at 96 hpf. In addition, exposure to TBECH diminished free swimming distance both in the light and under a photoperiod of 10 min light/10 min dark cycles in zebrafish larvae at 6 days post-fertilization (dpf). Moreover, exposure to TBECH elevated activities of superoxide dismutase (SOD) and catalase (CAT), malondialdehyde (MDA) content, whereas it reduced glutathione (GSH) content, in zebrafish larvae at 6 dpf. Accordingly, RT-qPCR analysis demonstrated that TBECH exposure increased the mRNA levels of sod1, sod2, cat, and gpx1 in zebrafish larvae at 6 dpf. With respect to the immune aspect, the mRNA levels of pro-inflammatory genes, including il-1b, il-6, il-8, and tnfa, in larval zebrafish at 6 dpf were increased by exposure to TBECH, while pretreatment with TBECH inhibited 24 h of exposure to LPS-stimulated elevation in the mRNA levels of the abovementioned four pro-inflammatory genes in zebrafish larvae at 6 dpf. Furthermore, TBECH treatment increased caspase-3 enzyme activities and regulated apoptosis-related genes in larval zebrafish at 6 dpf. Taken together, the data obtained in this study demonstrated that TBECH caused developmental and locomotor behavioral toxicity, immunotoxicity, oxidative stress and proapoptotic effects in early life zebrafish. The present study will help to understand the comprehensive toxicity of TBECH in zebrafish.