Immune Response Of Rainbow Trout Research Articles

Extract of common mallow (Malvae sylvestris) enhances growth, immunity, and resistance of rainbow trout (Oncorhynchus mykiss) fingerlings against Yersinia ruckeri infection

The dietary effects of a native medicinal plant from Iran, common mallow (Malvae sylvestris), was evaluated on growth performance, innate immune parameters, mucosal immune parameters, and resistance of rainbow trout (Oncorhynchus mykiss) against Yersinia ruckeri. Therefore, 360 fish (initial weight 10.42 ± 0.09 g) were randomly distributed into 12 fiberglass tanks. Experimental diets supplemented with 0 (as control- C), 1% (M1), 3% (M2) and 5% (M3) levels of M. sylvestris flowers extract were fed to the fish based on 3% of body weight for 8 weeks. At the terminal sampling, growth performance, liver and digestive enzymes activities, blood and mucosal immune responses were determined. Results showed that M2 and M3 had greater final weight, weight gain, SGR, survival rate and lower FCR; higher levels of total protein, albumin, globulin, and lower cortisol levels in comparison to control; 5% extract also lowered cholesterol and glucose levels as well as Lactate Dehydrogenase (LDH) activity. We reported higher values of hematocrit, hemoglobin, Mean Corpuscular Hemoglobin (MCH), Mean Corpuscular Volume (MCV), White Blood Cell (WBC), Red Blood Cell (RBC) and lymphocytes for treated groups. Innate immune responses (Alternative complement activity (ACH50) in M2 and M3 group, total Immunoglobulin (Ig) and lysozyme in M3), mucosal immune parameters (ACH50, total Ig for M2 and M3 group and lysozyme in all treated groups) were enhanced. Activities of digestive enzymes (protease in all treated groups, amylase for 3 and 5%, while lipase only for 5%) and lower activity of liver ALT enzyme in individuals treated with highest dose was observed. Overall results indicated that the extract can positively affect growth performance and immune responses of rainbow trout.

Effects of Lipopolysaccharides (LPS) of Yersinia ruckeri on Immune Response in Rainbow Trout (Oncorhynchus mykiss) by Intraperitoneal and Oral Administration

BACKGROUND: Recently, the researches about herbal medicines as substitutes for chemical drugs have risen in number. OBJECTIVES: To add more aspects to this research area, this study evaluated the changes in biochemical factors of the blood serum due to the consumption of Thymus daenensis extract and the effect of the period of its consumption into the diet of herd dogs. METHODS: Eight adult male dogs were chosen and fed with a fixed diet for 1 month. Then they were ran- domly assigned to two groups of four. The members of first (control) group were fed only with the fixed diet and the second group received 200mg/ml, administered as 1ml/kg of Thymus daenensis extract into their fixed diet. Finally, the dogs were bloodlet at 3 different times, namely before intervention, 7 and 14 days after the in- tervention to measure the factors of glucose, cholesterol, triglyceride, LDL and HDL, alanine aminotransferase and aspartate aminotransferases. RESULTS: Comparing to the control group and the starting point of this experiment, levels of FBS, LDL, TGL, CHOL, AST factors significantly decreased 14 days after intervention, but the HDL factor increased after 7 and 14 days of intervention (P 0.05). CONCLUSIONS: Consequently, oral consumption of Thymus daenensis extract led to decrease in the amounts of glucose and lipids of blood and this herb can be recommended for treating diabetics and persons suffering from high cholesterol.

Effect of lemon balm (Melissa officinalis) extract on growth performance, digestive and antioxidant enzyme activities, and immune responses in rainbow trout (Oncorhynchus mykiss).

This study was conducted to determine the effects of dietary supplementation of lemon balm (Melissa officinalis) aqueous methanolic extract on growth performance, blood parameters, digestive and antioxidant enzyme activities, and non-specific immune responses in rainbow trout (Oncorhynchus mykiss). Fish with an average weight of 23.03 ± 0.07g were fed a diet supplemented with an aqueous methanolic extract of lemon balm at a dose of 0 (control), 0.1 (LB0.1), 0.5 (LB0.5), and 1gkg-1 (LB1) for 75days. The final weight, weight gain, and specific growth rate were observed to be significantly increased in LB0.5 and LB1 groups compared with that of the control. No differences were observed in feed conversion ratio values. WBC increased at the 45th day of the study in LB0.1 group. No differences were determined in RBC (P > 0.05). At the end of the study, lipase increased significantly in all experimental groups compared with the control. Pepsin was also elevated in LB0.5 and LB1 groups compared with the control. Increased trypsin was determined in LB1 group (P < 0.05). SOD activity increased at the end of the study in LB1 group (P < 0.05). CAT values had no differences compared with control. GR activity increased in all experimental groups compared with control. GPx improved in LB0.5 and LB1 groups significantly (P < 0.05). Lipid peroxidation was decreased in LB1 group compared with that of control, but this decrease was not significant (P < 0.05). Oxidative radical production and lysozyme activity significantly increased in LB1 group (P < 0.05). The highest MPO was determined in control group (P < 0.05). Current results suggest that lemon balm extract stimulates growth promoting antioxidant and immune responses in rainbow trout.

Short-term effects of feeding powdered Aloe vera (Aloe barbadensis) and nettle (Urtica dioica) on growth performance and stimulation of innate immune responses in rainbow trout (Oncorhynchus mykiss)

To evaluate the nutritional impacts of powdered Aloe vera and nettle plants on growth performance and some parameters of immune response in rainbow trout, a total of 462 fish with an average weight of 10.80 ± 0.59 g were obtained from authentic fish farms. The fish were fed in seven groups with diets containing 0.5, 1, and 1.5% of Aloe vera powder and 0.5, 1, and 1.5% of nettle powder, and also a control with a basal diet without herbal supplementation for 4 weeks. The results of fish biometry showed that dietary supplementation with the powdered plants led to significant differences in weight gain, specific growth rate, feed conversion ratio, and feed efficiency ratio with 1.5% of Aloe vera and 0.5% of nettle supplementations compared with the control group. The treatments displayed increased hematological parameters as well as serum biochemical parameters. Serum lysozyme and complement system activities elevated due to dietary supplementations with the best results found in treatments with 1.5% of Aloe vera and 0.5% of nettle. However, despite an increase in respiratory burst activity of leukocytes in fish fed with powdered plants, no significant differences were observed as opposed to the control.

Effects of temperature and photoperiod on rainbow trout (Oncorhynchus mykiss) smoltification and haematopoiesis

• nkaα1a , nkaα1b and nkcc1a provide relevant information that the NKA activity does not reflect. • While nkaα1a and nkcc1a transcription are mainly regulated by temperature, nkaα1b is regulated mainly by photoperiod. • High water temperature could potentially compromise the adaptive and innate immune response of rainbow trout. • Increased water temperature (8 °C) during winter does not provide clear advantages for smoltification or size at harvesting.

The effects of starvation on some epidermal mucus immune parameters in rainbow trouts

The skin of a fish acts as the primary protective agent against biological, physical, and chemical stress. However, the effects of such stressors on fish mucosal immune responses have been hardly investigated. Fasting or feed deprivation commonly is occurred in aquaculture due to season, production policies, or disease. This research was aimed to investigate the impacts of 20-day starvation on skin mucosal immune responses of rainbow trout. The results revealed that the enzymatic activities of lysozyme (LZM) and alkaline phosphatase (ALP), as well as the total immunoglobulins (Ig) level and bactericidal activities were significantly reduced in the skin mucus of fasted fish. No significant changes were observed in the esterase and protease activities. Bactericidal activity in the mucus of starved fish was significantly lower than control group after 20 days. Therefore, it could be strongly suggested that this species should not remain under starvation stress as this kind of stress impairs mucosal immune barriers which, in turn, could make the fish more susceptible to infections or harmful agents.

Enhancing innate antiviral immune responses in rainbow trout by double stranded RNA delivered with cationic phytoglycogen nanoparticles

Innate immunity is induced when pathogen-associated molecular patterns (PAMPs) bind host pattern recognition receptors (PRRs). Polyinosinic:polycytidylic acid [poly(I:C)] is a synthetic analogue of viral dsRNA that acts as a PAMP, inducing type I interferons (IFNs) in vertebrates. In the present study, the immunostimulatory effects of high molecular weight (HMW) poly(I:C) in rainbow trout cells were measured when bound to a cationic phytoglycogen nanoparticle (Nano-HMW). The physical characteristics of the nanoparticle itself, when bound to different lengths of dsRNA and when cell associated was evaluated. Optimal concentration and timing for innate immune stimulation was measured using the RTG-P1 reporter cell line. The immunostimulatory effects of HMW poly (I:C) was compared to Nano-HMW in vitro using the RTgutGC cell line cultured in a conventional monolayer or a transwell culture system. The ability of an activated intestinal epithelium to transmit an antiviral signal to macrophages was evaluated using a co-culture of RTgutGC cells and RTSll (a monocyte/macrophage cell). In all culture conditions, Nano-HMW was a more effective inducer of IFN-related antiviral immune responses compared to HMW poly (I:C) alone. This study introduces the use of cationic phytoglycogen nanoparticles as a novel delivery system for immunomodulatory molecules to enhance immune responses in aquatic vertebrates.

Genome-Wide Association Analysis for Resistance to Infectious Pancreatic Necrosis Virus Identifies Candidate Genes Involved in Viral Replication and Immune Response in Rainbow Trout (Oncorhynchus mykiss).

Infectious pancreatic necrosis (IPN) is a viral disease with considerable negative impact on the rainbow trout (Oncorhynchus mykiss) aquaculture industry. The aim of the present work was to detect genomic regions that explain resistance to infectious pancreatic necrosis virus (IPNV) in rainbow trout. A total of 2,278 fish from 58 full-sib families were challenged with IPNV and 768 individuals were genotyped (488 resistant and 280 susceptible), using a 57K SNP panel Axiom, Affymetrix. A genome-wide association study (GWAS) was performed using the phenotypes time to death (TD) and binary survival (BS), along with the genotypes of the challenged fish using a Bayesian model (Bayes C). Heritabilities for resistance to IPNV estimated using genomic information, were 0.53 and 0.82 for TD and BS, respectively. The Bayesian GWAS detected a SNP located on chromosome 5 explaining 19% of the genetic variance for TD. The proximity of Sentrin-specific protease 5 (SENP5) to this SNP makes it a candidate gene for resistance against IPNV. In case of BS, a SNP located on chromosome 23 was detected explaining 9% of the genetic variance. However, the moderate-low proportion of variance explained by the detected marker leads to the conclusion that the incorporation of all genomic information, through genomic selection, would be the most appropriate approach to accelerate genetic progress for the improvement of resistance against IPNV in rainbow trout.

Effect of sulfated polysaccharides extracted from marine macroalgae (Ulva intestinalis and Gracilariopsis persica) on growth performance, fatty acid profile, and immune response of rainbow trout (Oncorhynchus mykiss)

Supplementation of seaweed to fish diets has been widely reported to improve growth and immunity. This study was conducted to investigate the effect of sulfated polysaccharide extract from the green alga Ulva intestinalis and the red alga Gracilariopsis persica as a dietary supplement on growth performance, fatty acid profile, stress response, antioxidant enzyme activity, and nonspecific immune responses in rainbow trout (Oncorhynchus mykiss) (15.74 ± 0.48 g). The five experimental diets include control (without sulfated polysaccharide), 0.5SPG (0.5 g kg−1 sulfated polysaccharide from G. persica), 1.5SPG (1.5 g kg−1 sulfated polysaccharide from G. persica), 0.5SPU (0.5 g kg−1 sulfated polysaccharide from U. intestinalis), and 1.5SPU (1.5 g kg−1 sulfated polysaccharide from U. intestinalis) were formulated and fed to fish for 8 weeks. Results of growth trial indicated a significant enhancement of growth performance of fish fed 1.5SPG, 0.5SPU, and 1.5SPU as compared with control. Although there was no significant difference in the fatty acid profile of muscle, fish fed the 1.5SPG diet showed higher protein and lower lipid contents than the control group. While the lysozyme and complement activity of serum was significantly enhanced in fish fed 1.5SPG and 1.5 SPU diets, superoxide dismutase in these treatments was lower than the control group. Furthermore, the amount of cortisol in individuals fed experimental diets after 3-h confinement stress was lower than fish fed the control diet. To conclude, in consideration of all factors, we suggest the potential benefits of using 1.5SPG diet in the aquaculture industry as a diet supplementation.

Protec™ improves innate immune response and specific antibody response against Lactococcus garvieae in rainbow trout (Oncorhynchus mykiss)

Protec™ is a commercial aquafeed (Skretting Italia) containing a combination of glucans, vitamin C, vitamin E and zinc (immune support pack). No research information concerning its capability to improve fish immune response is available, so in this study the potential immunomodulatory effects of Protec™ were investigated in rainbow trout (Oncorhynchus mykiss). Head kidney (HK) leukocytes from adult fish (100 g, n = 6) were in vitro incubated with Protec™ immune support pack resulting in significantly higher respiratory burst activity and proliferation. Specifically, sonicated Protec™ immune support pack (160 μg/ml) induced a respiratory burst response similar to that promoted by zymosan and lipopolysaccharide (LPS), while non-sonicated Protec™ immune support pack induced a response comparable to that of cells stimulated with phorbol myristate acetate (PMA). Moreover, the proliferation of leukocytes exposed to sonicated Protec™ immune support pack (20 μg/ml) was significantly higher than that of cells stimulated with zymosan, and it was comparable to the proliferation of cells stimulated with phytohaemagglutinin (PHA) and LPS. Afterwards, a feeding trial was performed in a rainbow trout farm. Two groups of juvenile rainbow trout (10 g) were acclimated for 7 weeks before the experiment and fed daily with a commercial control diet (Optiline HE, Skretting Italia) at 2% BW/day. At the end of acclimation, one group of fish was fed with Protec™ diet (Skretting Italia) at 2% BW/day whereas the other group continued to feed the control diet at the same level for further 4 weeks. Then, fish were sampled (HK leukocytes from n = 6 fish/group, serum from n = 12 fish/group) or intraperitoneally vaccinated against lactococcosis (n = 160/dietary group/time point). Fish fed the same diets for further 4 weeks after vaccination, then feeding returned to the control diet in both groups until the end of the trial. The specific antibody response was recorded at 4 and 8 weeks after vaccination (n = 12 fish/group). The administration of Protec™ significantly enhanced the respiratory burst activity of leukocytes and the synthesis of specific IgM against Lactococcus garvieae, whereas the serum lysozyme activity was unaffected. The present research suggests that the administration of Protec™ can improve both innate and adaptive immune response of rainbow trout, proving to be an interesting strategy for enhancing the immune reactivity of fish to vaccines.

NKEF, an antiviral protein involved in the immune response of rainbow trout red blood cells

NKEF, an antiviral protein involved in the immune response of rainbow trout red blood cells

The differential regulating roles of mTOR signaling on IGM+ and IGT+ B cells in systematic and mucosal immune responses of rainbow trout

The differential regulating roles of mTOR signaling on IGM+ and IGT+ B cells in systematic and mucosal immune responses of rainbow trout

Development of a live vector vaccine against infectious hematopoietic necrosis virus in rainbow trout

Infectious hematopoietic necrosis virus (IHNV) leads to serious disease and economic losses in the salmonid aquaculture industry. The present study aimed to develop an effective and efficient vaccine to protect rainbow trout (Oncorhynchus mykiss) against IHNV infection. Administered via the immersion route, a live vector vaccine containing the regions of the IHNV glycoprotein (G) induced immune responses in rainbow trout. Use of the immersion route induced more-efficient mucosal immunity than intramuscular injection vaccination. IHNV G gene expression was detected in the spleens of rainbow trout at 3, 7 and 15 days post-vaccination (dpv). The G gene expression continuously decreased between 3 and 15 dpv. In addition, the expression of TLR-3, TLR-7 and TLR-8 was upregulated after vaccination, and the highest expression levels of IFN-1, Mx-1, Mx-3, Vig-1 and Vig-2 were observed at 3 dpv. Four markers of the adaptive immune response (CD4, CD8, IgM and IgT) gradually increased. When experimental fish were challenged with IHNV by immersion, significant differences in cumulative percentage mortality were observed in the vaccinated fish and the unvaccinated (empty-plasmid-vaccinated) fish. The relative survival rate was 92% and 6% in the vaccinated group and empty-plasmid group, respectively. Serum antibody levels gradually increased in the vaccinated fish, unlike in the unvaccinated fish, after 7 dpv. Our results suggest there was a significant increase in fish immune responses and resistance to infection with IHNV following administration of the live vector vaccine. Therefore, this live vector vaccine is a promising vaccine that may be utilized to protect rainbow trout against IHNV.

Application of Spirulina in aquaculture: a review on wastewater treatment and fish growth

AbstractThere is an urgent need to find alternatives to fish meal and fish oil in compound feeds due to their rapidly rising prices and the demand for sustainable fisheries. Spirulina, a filamentous blue‐green microalga, is an excellent source of plant protein and could replace expensive animal‐derived proteins in fish feed. Studies have evaluated the use of spirulina as a fish meal for different fish species. This paper reviews research on the effects of spirulina on the growth performance of various fish species. It is apparent that spirulina can be a highly important component of the diet of fish; it has a number of benefits, such as promoting the growth of tilapia (Oreochromis niloticus) and carp (Labeo rohita), improving the reproductive performance of yellow tail cichlid (Pseudotropheus acei) and enhancing the immune response of rainbow trout (Oncorhynchus mykiss). Recent studies have shown that spirulina can be used for treating wastewater, including effluent from fish culture activities, as it can efficiently metabolize the nutrients and remove the heavy metals contained in aquaculture effluent. Fish aquaculture could apply an integrated strategy of simultaneously treating aquaculture effluent while producing spirulina biomass to supplement fish diets.

Skin immune response of rainbow trout (Oncorhynchus mykiss) experimentally exposed to the disease Red Mark Syndrome

Red Mark Syndrome (RMS) is a skin disease reported from farmed rainbow trout. Since the turn of the millennium it has been spreading through Europe. RMS is probably a bacterial disease caused by a Midichloria-like organism (MLO). It is non-lethal and causes little obvious changes in appetite or behavior but results in red hyperaemic skin lesions, which may lead to economic losses due to downgrading. Here we transfer RMS to naïve specific pathogen free (SPF) fish by cohabitation with RMS-affected seeder fish. During disease development we characterize local cellular immune responses and regulations of immunologically relevant genes in skin of the cohabitants by immunohistochemistry and qPCR. Skin samples from SPF controls and cohabitants (areas with and without lesions) were taken at 18, 61, 82 and 97 days post-cohabitation. Gene expression results showed that lesions had a Th1-type profile, but with concurrent high expression levels of all three classes of immunoglobulins (IgD, IgM and IgT). The marked local infiltration of IgD + cells in the skin lesions as well as a highly up-regulated expression of the genes encoding sIgD and mIgD indicate that this immunoglobulin class plays an important role in skin immunity in general and in RMS pathology in particular. The co-occurrence of an apparent B cell dominated immune reaction with a Th1-type profile suggests that the local production of antibodies is independent of the classical Th2 pathway.

The skin immune response of rainbow trout, Oncorhynchus mykiss (Walbaum), associated with puffy skin disease (PSD)

Puffy skin disease (PSD) is an emerging skin condition which affects rainbow trout, Oncorhynchus mykiss (Walbaum). The transmission pattern of PSD suggests an infectious aetiology, however, the actual causative infectious agent(s) remain(s) unknown. In the present study, the rainbow trout epidermal immune response to PSD was characterised. Skin samples from infected fish were analysed and classified as mild, moderate or severe PSD by gross pathology and histological assessment. The level of expression of 26 immune-associated genes including cytokines, immunoglobulins and cell markers were examined by TaqMan qPCR assays. A significant up-regulation of the gene expression of C3, lysozyme, IL-1β and T-bet and down-regulation of TGFβ and TLR3 was observed in PSD fish compared to control fish. MHCI gene expression was up-regulated only in severe PSD lesions. Histological examinations of the epidermis showed a significant increase in the number of eosinophil cells and dendritic melanocytes in PSD fish. In severe lesions, mild diffuse lymphocyte infiltration was observed. IgT and CD8 positive cells were detected locally in the skin of PSD fish by in situ hybridisation (ISH), however, the gene expression of those genes was not different from control fish. Total IgM in serum of diseased animals was not different from control fish, measured by a sandwich ELISA, nor was significant up regulation of IgM gene expression in PSD lesions observed. Taken together, these results show activation of the complement pathway, up-regulation of a Th17 type response and eosinophilia during PSD. This is typical of a response to extracellular pathogens (i.e. bacteria and parasites) and allergens, commonly associated with acute dermatitis.

Effects of different cytokines on immune responses of rainbow trout in a virus DNA vaccination model.

Seven rainbow trout cytokine genes (interleukin (IL)-2, IL-8, IL-15, IL-17, IL-1β, intracellular interferon (iIFN) 1a, and IFN-γ2) were evaluated for their adjuvant effects on a DNA vaccine, called pG, containing the glycoprotein gene of infectious hematopoietic necrosis virus (IHNV). Distinct DNA constructs in expression plasmid pcDNA3.1 encoding a cytokine gene were generated. Immunofluorescence assays in rainbow trout gonadal cells demonstrated successful protein expression from all these constructs. Subsequently, fish were immunized with pG alone or together with a cytokine expression plasmid. Results showed that each cytokine plasmids at an appropriate dose showed notable effects on immune gene expression. IL-17 and IFN-γ2 can enhance early specific IgM response. All cytokines, except IL-8, can benefit initial neutralizing antibody (NAb) titers. At 35 days post immunization (dpi), NAb titers of fish immunized with pG and IL-2, iIFN1a, or IFN-γ2 plasmids remained at high levels (1:160). NAb titers of fish immunized with pG alone decreased to 1:40. IL-8 or IL-1β can enhance antigen-specific proliferative T-cell responses at 14 dpi. At 28 dpi, coinjection of pG with IL-2, IL-8, IL-15, or IL-17 plasmids induced considerably stronger lymphocyte proliferation than that with injection of pG alone. All cytokine plasmids delivered with pG plasmid enhanced protection of trout against IHNV-mediated mortality. These results indicate that the type and dose of trout cytokine genes injected into fish affect quality of immune response to DNA vaccination.

CK12a, a CCL19-like Chemokine That Orchestrates both Nasal and Systemic Antiviral Immune Responses in Rainbow Trout.

Chemokines and chemokine receptors have rapidly diversified in teleost fish but their immune functions remain unclear. We report in this study that CCL19, a chemokine known to control lymphocyte migration and compartmentalization of lymphoid tissues in mammals, diversified in salmonids leading to the presence of six CCL19-like genes named CK10a, CK10b, CK12a, CK12b, CK13a, and CK13b. Salmonid CCL19-like genes all contain the DCCL-conserved motif but share low amino acid sequence identity. CK12 (but not CK10 or CK13) is constitutively expressed at high levels in all four trout MALT. Nasal vaccination with a live attenuated virus results in sustained upregulation of CK12 (but not CK10 or CK13) expression in trout nasopharynx-associated lymphoid tissue. Recombinant His-tagged trout CK12a (rCK12a) is not chemotactic in vitro but it increases the width of the nasal lamina propria when delivered intranasally. rCK12a delivered intranasally or i.p. stimulates the expression of CD8α, granulysin, and IFN-γ in mucosal and systemic compartments and increases nasal CD8α+ cell numbers. rCK12a is able to stimulate proliferation of head kidney leukocytes from Ag-experienced trout but not naive controls, yet it does not confer protection against viral challenge. These results show that local nasal production of CK12a contributes to antiviral immune protection both locally and systemically via stimulation of CD8 cellular immune responses and highlight a conserved role for CK12 in the orchestration of mucosal and systemic immune responses against viral pathogens in vertebrates.

Extended fasting does not affect the liver innate immune response in rainbow trout

Activation of immune response pathway is energy demanding. We tested the hypothesis that negative energy balance will curtail the liver's capacity to evoke an immune response in rainbow trout (Oncorhynchus mykiss). Fish were either fed or fasted for 118 d and challenged with lipopolysaccharide (LPS) to determine the liver capacity to elicit an immune response. Fasting led to negative specific growth rate, reduced tissue metabolite levels, and higher transcript abundance of SOCS-2. LPS treatment increased the liver transcript abundances of IL-1β and IL-8 and serum amyloid protein A, while SOCS-2 was reduced. LPS lowered plasma cortisol level only in the fasted fish, but did not affect liver glucocorticoid or mineralocorticoid receptor protein expressions. Extended fasting did not suppress the liver capacity to evoke an immune response. Upregulation of liver SOCS-2 may be playing a key role in the energy repartitioning, thereby facilitating immune response activation despite extended fasting in trout.

Effects of Aloe Vera crude extract on growth performance and some hemato-immunological indices of Oncorhynchus mykiss in farm scale

BACKGROUND: The immunostimulating effect of Aloe vera in mammals has been documented, but few works were done on effect of A. vera on fish health and immune responses. OBJECTIVES: In this study the effect of oral administration of A. vera on growth indices, hematological parameters and immune responses of rainbow trout were investigated. METHODS: One thousand five hundred rainbow trout fingerling (20 ± 2 g, Mean ± SD) were divided into five groups, each in triplicate, in farm scale. Group 1 were adopted as control and fed with non-supplemented feed, groups 2 to 5 were fed with diet supplemented by 0.05%, 0.1%, 0.2% and 0.5% A. vera extract respectivly for 60 days. Growth indices (SGR, FCR, PWG, FER, PER and CF) calculated in day 30 and 60. Blood samples were taken in day 60 and hematological parameters including: PCV, Hb, RBC, WBC, MCH, MCV, MCHC as well as immunological parameters including: Lysozyme and serum bactericidal activity, serum total protein and globulin were compared among the groups. RESULTS: Results showed that all calculated growth indices (except CF) and all mentioned immunological parameters were significantly increased in fish fed with 0.1% and 0.2% A. vera supplemented food (G3 and G4) compare to control group (P 0.05). CONCLUSIONS: It can be concluded that oral administration of 0.1% and 0. 2% A. vera crud extract in food (G3 and G4) can improved growth indices, stimulate non-specific immune responces and affect some hematological parameters positively in rainbow trout.