Immunostimulants added to injected Aeromonas salmonicida bacterin enhance the defense mechanisms and protection in rainbow trout (Oncorhynchus mykiss)

The Synergic Effect of Gut-Derived Probiotic Bacillus cereus SL1 And Ocimum sanctum on Growth, Intestinal Histopathology, Innate Immunity, and Expression of Enzymatic Antioxidant Genes in Fish, Cirrhinus mrigala (Hamilton, 1822)

An effective alternative approach to combat aquaculture challenges is the strategic application of bioresources, which not only mitigate disease ailment but also optimize fish growth. Hence, current research was undertaken to highlight the synergic role of bioresources such as plant immunostimulant Ocimum sanctum along with potent gut-derived probiotic Bacillus cereus strain SL1 (Gen Bank Accession Number: FJ627945.1) on mrigal (Cirrhinus mrigala) growth, antioxidant status, gut histopathology, and immune response. For 90 days, fingerlings (average weight 6.8 ± 0.5 g) were fed on diets having varying concentrations of O. sanctum and B. cereus. After the completion of the feeding trial, various growth, immunity, and histological and antioxidant metrics were evaluated according to standard procedures. In comparison to the control and other treatment groups, T3 group showed a significant (P < 0.05) increase in growth parameters, antioxidant enzymatic activity, and hematological and immunological parameters. In addition to it, supplementation of both B. cereus and O. sanctum also upregulated the antioxidant-related gene expressions, such as hepatic catalase gene by 1.89-3.00 folds, hepatic SOD-1 by 4.46-7.52 folds, and GPx-1of the liver by 1.56-1.95 folds. For 10 days, fingerlings were challenged with the pathogenic bacterium Aeromonas hydrophila (MTCC-1739), and maximum survival rate (77.77%) was reported in fingerlings of T3 treatment. Further histopathological studies of gut tissues affirm that O. sanctum and B. cereus play a synergic role in the protection of digestive organs from the pathogenic bacterium A. hydrophila. These results suggest that O. sanctum and B. cereus synergically improved the growth performance, immunity, antioxidant status, and gut histology of C. mrigala leading to its sustainable culture.

Effect of Dietary Origanum onites on Growth, Non Specific Immunity and Resistance against Yersinia ruckeri of Rainbow Trout ( Oncorhynchus mykiss)

Natural substances has been identified to maintain health and improve growth performance in the aquaculture. The effect of Origanum onites on growth and immune response of rainbow trout was investigated. Experimental groups (A and B) of 70 fish were separated into 10 different treatments. A groups were fed with dietary administration of O. onites essential oil (0.5 mL kg-1 and 3.0 mL kg-1) and crude powder (1.0 g kg-1 and 10.0 g kg-1) for a period of 8 weeks. Other groups (B) were vaccinated against Yersinia ruckeri at the beginning of experiment and then fed the same diets described above. Results showed that feed conversion ratio in fish fed a combination of O. onites and vaccine was statistically better than the control. NBT-positive cells, phagocytic activity, serum lysozyme activity and immunoglobulin M level were stimulated in both non vaccinated and vaccinated fish (p<0.05). Cumulative mortality in fish fed O. onites was lower than controls following challenge with Y. ruckeri. No mortality was observed in vaccinated fish fed with 0.5 mL kg-1 of O. onites. These results indicated that dietary administration of O. onites could act as an enhanced non specific immune response, growth performance and resistance to Y. ruckeri.

Role of Zingiber officinale and autochthonous probiotic Bacillus coagulans in feeds of Catla catla (Hamilton, 1822) for growth promotion, immunostimulation, histoprotection, and control of DNA damage

Experiment was conducted to assess the impact of ginger (Zingiber officinale) as a dietary supplement with probiotic bacterium Bacillus coagulans on growth performance, hematological parameters, and non-specific immune parameters in Catla catla. An attempt was also made to investigate their effects on histology and extent of DNA damage against pathogenic bacterium Aeromonas hydrophila in C. catla. Ten dietary treatments were designed in triplicate in which five groups of fingerlings fed on diets containing different incorporation level of dried ginger at 0 g kg-1 (C1; basal diet 1 with duckweed as major protein source), 1 g kg-1 (G1), 5 g kg-1 (G2), 10 g kg-1 (G3), and 15 g kg-1 (G4) and other five groups of fingerlings fed on diets (G5-G9) containing different incorporation level of dried ginger at 0, 1, 5, 10, and 15 g kg-1 along with probiotic bacterium B. coagulans @ 3000 CFU ml-1 for 90 days. Results clearly revealed significantly (P < 0.05) high values of weight gain, growth % gain in body weight, specific growth rate (SGR), RBC and WBC count, phagocytic activity, respiratory burst activity, serum protein, and serum bactericidal activity in group of fingerlings fed on ginger supplemented diets which further improved with the inclusion of probiotic with best results in treatment G8. Histopathological study and COMET assay reflected that Z. officinale and probiotics protect extent of DNA damage and the digestive organs from the detrimental effects of pathogenic bacteria affirming their positive role and harmonious effects of probiotic bacterium with Z. officinale-supplemented diets.

Immunity and growth improvement of rainbow trout (Oncorhynchus mykiss) fed dietary nettle (Urtica dioica) against experimental challenge with Saprolegnia parasitica

In this study, effects of nettle (Urtica dioica) on growth, immunity, and gene expressions were examined in rainbow trout after an 8-week feeding period. A total of 264 juvenile rainbow trout (10.72 ± 0.55 g) were selected and stocked randomly in 12 aquaria. Nettle powder was added to the fish feed at three doses, 0.5,1 and 1.5% served as treatments. At the end of 8-week feeding period, the fish were exposed to Saprolegnia parasitica for 3 weeks. Results showed that all treatments fed with nettle diets exhibited significant increases in weight gain and SGR, and decreased FCR compared to the control. Feeding the fish with dietary nettle resulted in significant rises in blood indices and non-specific immunity in comparison with the control. Furthermore, fish fed 0.5% of dietary nettle showed significantly increased expressions of TNF-α, IL-1b, IL-6 and IL-8 genes following 8 weeks of feeding. A significant reduction in mortality rate was observed in the fish treated with 0.5% of nettle compared to the control following challenging with S. parasitica. Our observations indicate that the use of 0.5% nettle powder in rainbow trout diet can improve growth and immunity parameters as well as fish resistance against S. parasitica contamination.

α-Enolase as a novel vaccine candidate against Streptococcus dysgalactiae infection in cobia (Rachycentron canadum L.)

Streptococcus dysgalactiae is an important pathogenic bacterium that has caused economic loss for the cobia industry in Taiwan, ROC. This study presents a highly effective subunit vaccine composed of a moonlight protein, α-enolase, for the prevention of S. dysgalactiae infection. First, α-enolase was cloned, transformed, and expressed in E. coli for production of recombinant protein. Then, the protective efficacies of α-enolase recombinant protein were evaluated in combination with either a pro-inflammatory cytokine, TNF-α, or an oil adjuvant, ISA 763 AVG. The results showed that the combination of α-enolase and ISA 763 AVG was highly protective (RPS = 88.89%), while a negative effect was found in the group immunised with α-enolase adjuvanted with TNF-α (RPS = 22.22%). A further study was conducted with double dose of ISA 763 AVG, which led to an increased RPS value of 97.37%. Moreover, immunised cobia exhibited significantly greater lysozyme activity, antibody responses, and expression of certain immune-related genes post-challenge. Altogether, our results demonstrated that a combination of α-enolase recombinant protein with ISA 763 AVG adjuvant is a promising vaccine that can be employed for protection of cobia against S. dysgalactiae infection.

Live vaccines against bacterial fish diseases: A review

Fish diseases are often caused either by bacteria, viruses, fungi, parasites, or a combination of these pathogens. Of these, bacterial fish diseases are considered to be a major problem in the aquaculture industry. Hence, the prevention of such diseases by proper vaccination is one of the integral strategies in fish health management, aimed at reducing the fish mortality rate in the aquaculture farms. Vaccination offers an effective yet low-cost solution to combat the risk of disease in fish farming. An appropriate vaccination regime to prevent bacterial diseases offers a solution against the harmful effects of antibiotic applications. This review discusses the role of live-attenuated vaccine in controlling bacterial diseases and the development of such vaccines and their vaccination strategy. The current achievements and potential applications of live-attenuated and combined vaccines are also highlighted. Vaccine development is concluded to be a demanding process, as it must satisfy the requirements of the aquaculture industry.

Growth performance, immune response, and digestive enzyme activity in Pacific white shrimp, Penaeus vannamei Boone, 1931, fed dietary microbial lysozyme

The present study investigates the effects of the dietary microbial lysozyme (ML) as an immunostimulant, on the growth performance, some immune parameters and digestive enzyme of Pacific white shrimp, Penaeus vannamei. Six hundred shrimps were obtained and randomly allocated into four groups as follows with three replicates. The shrimps were fed diets supplemented with 0 (control), 0.5, 1, and 2 g kg^-1 ML for 4 months. The results indicated that dietary supplementation of ML significantly improved final weight, weight gain, average daily weight gain rate (ADG), feed conversion rate (FCR), and feed efficiency rate (FER) compared to the control (P ˂ 0.05). However, weight gain specific growth rate (SGR) and survival rate were not significantly affected by dietary ML (P ˃ 0.05). Dietary ML had a progressive effects on some immune parameters status including total antioxidant capacity (TAOC), superoxide dismutase (SOD), glutathione peroxidase (GPX), lysozyme (LYZ), alkaline phosphatase (ALP), phenoloxidase (PO) and acid phosphatase (ACP) activity as well as differential haemocyte count (DHC) and total haemocyte count (THC), in shrimps treated with the lysozyme than untreated shrimps (P ˂ 0.05). However, feeding with ML had no significant effect on plasma malondialdehyde (MDA) level (P ˃ 0.05). Furthermore, intestinal digestive enzymes (lipase, protease, and amylase) in shrimp fed with dietary ML were significantly (P ˂ 0.05) higher than those fed with non-supplemented control basal diet. Thus, the results indicate that oral administration of ML can be recommended for shrimp feed to improve immune response as well digestive enzymes activity modulation.

Enhancement of broodstock health and maternal immunity in gilthead seabream (Sparus aurata L.) using ExcelMOS®

The current study was conducted to investigate the effect of ExcelMOS® in enhancing the immune system of Sparus aurata broodstock and their impact on offspring health through displaying the maternal transfer of immunity. Broodstock were divided into two groups: one was injected intraperitoneally with ExcelMOS® 1 month before spawning, while the other group was used as a control (without injection). Comprehensive increase in survival rate was observed for larvae hatched from ExcelMOS®-injected broodstock than those of the control (P ≤ 0.05). Hematological analysis showed increases in leukocyte count and hematocrit percentage (P ≤ 0.05) and significant enhancement in immune assays as phagocytic, respiratory burst, lysozyme activities in ExcelMOS®-injected broodstock (P ≤ 0.05). Additionally, total immunoglobulin levels in the serum, eggs, and larvae resulted from ExcelMOS®-injected broodstock were highly significant (P ≤ 0.05) than those in the control ones. Transmission electron microscopy and semi-thin sections in posterior intestine of ExcelMOS®-injected broodstock revealed reinforcement of the epithelial barrier structure, intestinal integrity, and functionality in combination with the stimulation of innate immune system. In conclusion, immunostimulation of Sparus aurata broodstock using ExcelMOS® has improved survival of larvae and enhanced both innate and adaptive immune defense mechanisms. Further investigations are required to show the effect of ExcelMOS® on fish cultured in intensive culture systems.

Muli bamboo (Melocanna baccifera) leaves ethanolic extract a non-toxic phyto-prophylactic against low pH stress and saprolegniasis in Labeo rohita fingerlings

Bamboo (Melocanna baccifera) plant plays a significant role in traditional Asian medicine and it can be used as an alternative to various chemo-therapeutics or prophylactic agents used in aquaculture. In the present study, the 1^st experiment was done for the preparation of extracts from bamboo leaves by using 90% alcohol as a solvent. In the 2^nd experiment, toxicity study was carried on Labeo rohita fingerlings (average length of 10.3 ± 1.5 cm and weight 18.5 ± 1.5 g) using BLAL (Bamboo Leaf Alcoholic) extract and it did not show any mortalities in fish even at the dose of 20 g kg^-1 body weight, which can be regarded as virtually non-toxic with minimal effect. The 3^rd experiment was conducted to find out the effect of BLAL extract based isocaloric and isonitrogenous feed (doses: control- 0.0%, diet T1-0.01%, diet T2-0.1%, diet T3-1% BLAL extract kg^-1 feed) on the haemato-immuno-biochemical parameters of L. rohita fingerlings (average length 15.7 ± 1.5 cm and weight 20.2 ± 1.5 g). Regular sampling was done (on 7^th, 15^th, 30^th and 60^th day of feeding) for different haematological, immunological and biochemical parameters. The study revealed that the best response occurred within 7 days of feeding with BLAL extract and long-term feeding have shown immunosuppressive condition in the fish. In the 4^th experiment, fish were exposed to multiple stressors like low pH stress, and Saprolegnia parastica infection after feeding with BLAL extract (0.1%) based feed for 7 days. The study showed that the BLAL extract can make fish resistant to single stress however, not able to reduce the fish mortality under multiple stresses (S. parastica infection under low pH). Thus, it can be concluded that the BLAL has the potentiality to be used as a non-toxic phyto-prophylactic which can induce non-specific immune response, reduces the low pH stress responses and increases the resistance against saprolegniasis under neutral pH condition in rohu fingerlings.

Aloe vera enhances the innate immune response of pacu (Piaractus mesopotamicus) after transport stress and combined heat killed Aeromonas hydrophila infection

In this study, pacu (Piaractus mesopotamicus) were fed with diets containing Aloe vera for 10 days prior to transport stress and infection with heat killed Aeromonas hydrophila. A. vera is popular around the world due to its medicinal properties, including immunostimulatory effects which was observed in this study. The results show that transport causes immunosuppression, an effect that was prevented by A. vera. Specifically, A. vera prevented reductions of both leukocyte respiratory burst and hemolytic activity of complement system caused by transport. Further, fish fed with A. vera also showed significantly higher leukocyte respiratory burst, serum lysozyme concentrations and activity of complement system 24 h after bacterial infection. Additionally, we observed that A. vera may modulate the innate response through activation of complement system during bacterial immune stimulation. In summary, A. vera extract enhanced innate immune parameters and consequently the ability of fish to cope with pathogens following transport stress. These findings show that A. vera has promise for use in aquaculture and add further evidence that medicinal herbs added to fish feed assist to prevent disease outbreaks.

Efficacy of a formalin-inactivated vaccine against Streptococcus iniae infection in the farmed grouper Epinephelus coioides by intraperitoneal immunization

Vaccination is the most effective means of preventing infectious diseases; however, few vaccines are effective against Streptococcus iniae (S. iniae) in grouper. This work presents an efficacious and safe vaccine against S. iniae infections in the grouper Epinephelus coioides. The vaccine candidate was the S. iniae GSI-310 strain. The vaccination was administered by intraperitoneal injection, and consisted of formalin-inactivated antigens combined with an AS-F or ISA763A adjuvant. Peripheral blood samples were collected for RT-qPCR and phagocytosis and agglutination assays. Our results indicated that immunoglobulin M (igm) was maximally expressed in the two vaccinated groups at 3 months post-secondary vaccination (PSV). A significant upregulation of mRNA expression for interleukin-1β (il-1β) and tumor necrosis factor-α (tnf-α) was also observed in fish treated with antigens combined with ISA763A, which peaked at 3 months PSV. In fish treated with antigens combined with AS-F, il-1β and tnf-α expression peaked at 14 days post-primary vaccination (PPV). Phagocytic activity and index increased significantly in the two vaccinated groups. Furthermore, fish in the two vaccinated groups exhibited significantly elevated agglutination titers compared to fish in the control group, in which almost no agglutination reaction was detected. In the efficacy test, the vaccinated and control groupers were treated with S. iniae at 1, 3, and 6 months PSV. The relative percentage survival (RPS) values of antigens with AS-F and antigens with ISA763A were both 100% at 1 and 3 months PSV; at 6 months PSV, the RPS values for these groups were 100% and 97.7%, respectively. Furthermore, the level of protection observed in the field trial closely resembled that achieved on a laboratory scale. Therefore, the proposed vaccine mixed with AS-F or ISA763A improved immune responses and provided safe and long-lasting protection in farmed groupers.

Effects of Prunella vulgaris labiatae extract on specific and non-specific immune responses in tilapia (Oreochromis niloticus)

We examined the effects of Prunella vulgaris Labiatae (P. vulgaris L.) on specific and non-specific immune responses of Nile tilapia, Oreochromis niloticus. The optimal concentration without toxicity of P. vulgaris was determined to 30-40 μg/ml in vitro and 120 μg/100 g of fish in vivo. P. vulgaris significantly elicited an antibody titer compared to FCA or β-glucan. β-glucan plus P. vulgaris group synergistically enhanced antibody production. No significant difference in antibody production was observed between P. vulgaris and P. vulgaris plus β-glucan group. A respiratory burst activity of head kidney (HK) leucocytes of tilapia administered with 300 or 500 μg P. vulgaris was significantly (p < 0.05) enhanced compared with the PBS-injected control group and FCA-treated group. Maximum increase in the NBT reduction value was observed in 500 μg P. vulgaris group but no significant difference was found between 300 and 500 μg P. vulgaris group. The level of serum lysozyme activity was significantly (p < 0.05) higher in the 300 and 500 μg P. vulgaris than 100 μg P. vulgaris and FCA group. The phagocytic activities of HK leucocytes from tilapia administered with 300 and 500 μg P. vulgaris were significantly (p < 0.05) higher than 100 μg P. vulgaris and the control group. P. vulgaris was revealed with a good immunoadjuvant evoking the specific and non-specific immune responses of tilapia.

Effects of praziquantel and sanguinarine on expression of immune genes and susceptibility to Aeromonas hydrophila in goldfish (Carassius auratus) infected with Dactylogyrus intermedius

Praziquantel and sanguinarine have been demonstrated positive therapeutic effects on monogenean Dactylogyrus intermedius; however, few studies have considered the post impacts of these antiparasitic chemicals on host after repelling the parasites. The changes of expression of selected immune genes (CCL-1, CXCL-8, IL-1β-1, IL-1β-2, TNFα-1, TNFα-2 and TGF-β) in gill, kidney and spleen and bacterial loads of Aeromonas hydrophila in gill, kidney, spleen and liver following bath administration of these antiparasitic chemicals were evaluated. The results showed that praziquantel and sanguinarine up-regulated to varying degrees of CXCL-8, IL-1β-1, IL-1β-2, TNFα-1 and TNFα-2 in gill, kidney and spleen. They both decreased the CCL-1 expression in gill while increased it in kidney and spleen. However, in all the tested tissues, the expression of TGF-β decreased in praziquantel treated goldfish whereas that increased in sanguinarine treated goldfish. The A. hydrophila challenge test showed that the praziquantel treatment enhanced the susceptibility to A. hydrophila while sanguinarine treatment decreased the susceptibility, as compared with the non-treated group. Overall, the results indicate that bath administration of praziquantel and sanguinarine modulates the immune related genes in goldfish and these may, to some extent, affect their ability to resist bacterial pathogens.

The effect of lycopene on oxytetracycline-induced oxidative stress and immunosuppression in rainbow trout (Oncorhynchus mykiss, W.)

The aim of this study was to determine the effects of lycopene on oxytetracycline (OTC)-induced oxidative stress and immunosuppression in rainbow trout. The experimental fish analysed in this study were divided into 6 different experimental groups. Group 1 was the control group, and groups 2, 3 and 4 received corn oil, lycopene and OTC, respectively, for 14 days. Group 5 received OTC for 14 days after lycopene pre-treatment for 14 days, while group 6 received OTC for 14 days before lycopene post-treatment for 14 days. Blood and tissue samples were collected at the end of the experiment and analysed for the oxidant-antioxidant status and changes in the immune response. There was a significant increase in the malondialdehyde level, which is an index of lipid peroxidation, and a decrease in superoxide dismutase, catalase, and glutathione peroxidase activity as well as a decrease in the glutathione level in the blood, liver, kidney and spleen of OTC-treated fish. Glutathione-S-transferase activity was significantly increased in the blood, liver, kidney and spleen samples of the group that received OTC alone. OTC also appeared to suppress specific and nonspecific immune system parameters, such as the haematocrit, leucocyte count, oxidative radical production (nitroblue tetrazolium activity), total plasma protein and immunoglobulin levels and phagocytic activity. Pre- and post-treatment with lycopene attenuated the OTC-induced oxidative stress by significantly decreasing the tissue malondialdehyde level. The superoxide dismutase, catalase and glutathione peroxidase activities as well as the glutathione levels were significantly increased with lycopene administration, while glutathione-S-transferase activity was significantly decreased. Lycopene administration was also associated with a significant increase in the OTC-suppressed immune system parameters in fish. Thus, the present results suggest that pre- and post-treatment with lycopene (10 mg per kg fish weight, delivered orally) may alleviate OTC-induced oxidative stress and immunosuppression.

Effect of Coriolus versicolor supplemented diet on innate immune response and disease resistance in kelp grouper Epinephelus bruneus against Listonella anguillarum

The effect of Coriolus versicolor extract supplemented diets on innate immune response and disease resistance in kelp grouper, Epinephelus bruneus against Listonella anguillarum, is reported. Kelp grouper were divided into four groups of 25 each and fed with C. versicolor enriched diets at 0% (control), 0.01%, 0.1%, and 1.0% level. After 30 days of feeding, all fish were injected interaperitoneally (i.p.) with 50 μl of L. anguillarum (4.7 × 10(7) CFU) to investigate the immune parameters at weeks 1, 2, and 4. The reactive oxygen species and reactive nitrogen species production were significantly enhanced in fish fed with 0.1% and 1.0% supplementation diets from weeks 1-4 when compared to the non enriched diet fed and infected control. The phagocytic activity significantly increased with 0.1% and 1.0% diets on weeks 2 and 4. The leucocyte myeloperoxidase content, lysozyme activity, and total protein level significantly increased when fed with 0.1% and 1.0% supplementation diets from weeks 1-4. The cumulative mortality was 35% and 45% in 1.0% and 0.1% enriched diet fed groups whereas it was 55% and 80% in 0.01% and 0% groups respectively. The present results suggest that diets enriched with C. versicolor at 0.1% or 1.0% level positively enhance the innate immune system and affords protection from L. anguillarum.

Protective effect of propolis against oxidative stress and immunosuppression induced by oxytetracycline in rainbow trout (Oncorhynchus mykiss, W.)

The aim of this study was to investigate the effects of propolis on oxytetracycline (OTC)-induced oxidative stress and immunosuppression in fish. OTC (100 mg per kg⁻¹ body weight) was orally administered to fish for 14 days. A significant elevation in the level of malondialdehyde, as an index of lipid peroxidation, and reductions in antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase) and low molecular weight antioxidant (reduced glutathione) levels were observed in the blood, liver, kidney, spleen, and heart tissues of OTC-treated fish. OTC also had a suppressive effect on specific and non-specific immune system parameters, such as leucocyte counts, oxidative radical production (nitrobluetetrazolium activity), total plasma protein and immunoglobulin levels, and phagocytic activity. Pre-treatment, post-treatment, and simultaneous treatment with propolis (50 mg per kg⁻¹ body weight, orally) attenuated the OTC-induced oxidative stress by significantly decreasing the levels of malondialdehyde in tissues. In addition, propolis significantly increased the level of reduced glutathione and the catalase, glutathione peroxidase, and superoxide dismutase activities. Upon the administration of propolis, the suppressed immune system parameters were significantly increased in fish treated with OTC. The present results suggest that pre-treatment, post-treatment, and simultaneous administration of propolis might alleviate OTC-induced oxidative stress and immunosuppression.

In vivo modulation of immune response and antioxidant defense in Atlantic cod, Gadus morhua following oral administration of oxolinic acid and florfenicol

Oxolinic acid and florfenicol are the commonly used antibiotics for the treatment of bacterial diseases in Atlantic cod, Gadus morhua. The changes in selected innate humoral immune response of the fish, bacterial proliferation in serum and transcriptional activity of selected immune and antioxidant defense-related genes following oral administration of these antimicrobial compounds were evaluated. Juvenile cod (75-100 g) were fed commercial feed coated with either florfenicol (10 mg kg(-1) fish, active ingredient) or oxolinic acid (20 mg kg(-1) fish, active ingredient) at a ration of 0.5% body weight for 10 days. Whole blood and serum samples were collected on the 10th day of feeding the antibiotics and at 3, 5 and 10 days after their withdrawal. Serum protein was significantly higher in fish at the 10th day post-withdrawal of both antibiotics. Florfenicol-fed fish had lower myeloperoxidase activity at 3 days post-withdrawal, while there were differential effects on alkaline phosphatase activity. Vibrio anguillarum and Aeromonas salmonicida were significantly reduced in the sera of antibiotics-fed fish until the 5th day post-withdrawal. Florfenicol could inhibit V. anguillarum better than oxolinic acid, while A. salmonicida was more susceptible than V. anguillarum upon treatment with both antibiotics. Furthermore, transcriptional profiles of selected genes related to bacterial defense, inflammation and antioxidant defense were dependent on the type of antibiotics that was administered and the time of sampling. These results indicate that oral administration of antibiotics modulates the immune response and antioxidant defense in Atlantic cod and these may, in turn, affect their ability to resist bacterial pathogens.

Dietary Korean mistletoe enhances cellular non-specific immune responses and survival of Japanese eel (Anguilla japonica)

The present study was performed to investigate the immunostimulatory effects of Korean mistletoe extract (KM-110; Viscum album Coloratum) on the non-specific immune response and protection against Aeromonas hydrophila infection in Japanese eel (Anguilla japonica). Eels were fed under 4 regimes, 0%, 0.1%, 0.5% and 1.0% KM-110 mixed diet. On day 14 after feeding, 15 fish from each group were injected i.p. with live A. hydrophila (3 x 10(6)CFU) and the remaining unchallenged fish from each group were used to study the innate immune response. On 14 days post-infection, the total survival rates were 26.6% in control, and 33.3%, 66.6% and 80% in 0.1%, 0.5% and 1% KM-110-treated groups, respectively. The maximum lysozyme activity was observed in the 1% KM-110-treated group. There was no significant difference of lysozyme activity between 0.1% and 0.5% KM-110 group. Superoxide anion (O(2)(-)) production was significantly (p<0.05) augmented in the 0.5% and 1% KM-110 groups compared to the control and 0.1% KM-110 group. No significant difference of (O(2)(-) production was found between 0.5% and 1% KM-110 group. Likewise, there was a significant increase in phagocytic activity in the 0.5% KM-110 group compared with the 0.1% group (p<0.05), but no significant difference between the 0.5% and the 1% KM-110 group indicating that 0.5% KM-110 concentration is suitable for stimulating maximum phagocytic activity resulting in a high amount of ROI production. Considering the present results, KM-110 could be utilized as a promising immunostimulating substance for a diet in aquaculture.

Influences of traditional Chinese medicine on non-specific immunity of Jian Carp (Cyprinus carpio var. Jian)

The influence of traditional Chinese medicine (TCM) formulation from Astragalus Root (Radix astragalin seu Hedysari) and Chinese Angelica Root (R. Angelicae Sinensis) at a ratio of 5:1 (w/w) on non-specific immunity of Jian carp, Cyprinus carpio var. Jian was investigated. The number of NBT-positive cells in the blood and lysozyme and complement activities in the serum of Carp fed with commercial feed supplemented with 1.0% (diet 1) and 1.5% (diet 2) TCM at 10 day of post-feeding were not different from those of the control group fed with feed unsupplemented TCM 10 days post-feeding (P>0.05), but at 20 and 30 days they increased significantly (P<0.05). The values of diet 1 group and diet 2 group at 20 day and at 30 day were not significantly different (P>0.05) from each other. In addition, the TCM formula increased body weight of experimental fish by about 16.84% (diet 1) and 19% (diet 2) above that of the control group. Therefore, these data suggest that the TCM formula could elevate the function of non-specific immunity of Jian carp. The optimal dosage added to commercial carp feed was 1.0% (w/w) and the oral administration time as a course of treatment was 20 days.

Cellulose beads bound to cellulose binding domain-fused recombinant proteins; an adjuvant system for parenteral vaccination of fish

A recombinant form of the outer membrane protein (A-layer protein) associated with atypical Aeromonas salmonicida was expressed, fused to a cellulose binding domain (CBD) isolated from Clostridium cellulovorans. The resultant chimerical protein was bound to either Sigmacell 20((R)) or Orbicell cellulose particles. Common goldfish were injected intraperitoneally with the cellulose-protein complex and blood serum antibody levels produced against A-protein were examined weekly by means of ELISA. These titers were compared to those induced by immunization of goldfish with the same protein, with or without Freund's incomplete adjuvant, as well as to a standard bacterin-adjuvant system. Small Orbicell beads (1-10 microM) induced antibody levels that were equal to the titers produced by the adjuvanted protein and bacterin formulae. In comparison, the larger Sigmacell particles (10-20 microM) proved to be poor immunopotentiators. The long-term titer elicited from a single injection of A-protein bound to Orbicell beads was equivalent to that induced by two injections. All the vaccinated fish demonstrated memory to the A-layer protein after exposure to a pathogenic load of atypical A. salmonicida with Orbicell treated fish displaying the highest titer. No direct correlation was found between the presence of anti-A-protein antibodies and protection against infection. The paper describes a simple and safe method to increase the potential immunogenicity of soluble recombinant proteins by employing relatively inexpensive cellulose particles.

Levamisole is a potent enhancer of gilthead seabream natural cytotoxic activity

Gilthead seabream (Sparus aurata L.) head-kidney (HK) leucocytes were incubated with 10(3) to 10(-4) ng levamisole/ml for 4, 24 or 48 h and then assayed for their natural cytotoxic activity against xenogeneic tumor cells. This activity was slightly increased after 24 h of incubation. In a second experiment, fish specimens were fed 0, 75, 150 or 300 mg levamisole/kg diet for 10 consecutive days. The fish were then fed a commercial non-supplemented diet and sampled 0, 1, 2, 3, 4 and 6 weeks post-administration of levamisole. The cytotoxic activity was found increased along the experiment and remained greatly enhanced at the end. In conclusion, levamisole enhanced seabream natural cytotoxic cell activity both in vitro and in vivo and had a great and lasting action when administered by feeding.

Evaluation of immune functions of rainbow trout (Oncorhynchus mykiss)--how can environmental influences be detected?

In fish, the first line of defense against infectious microorganisms is based on a broad range of nonspecific humoral and cellular immune mechanisms ("innate immunity") which without prior specific activation can act in forming a more static barrier (Fish Shellfish Immunol. 10 (2000) 243; Dev. Comp. Immunol. 25 (2001) 827). This natural resistance is normally effective enough to protect fish from infectious diseases until specific immune responses are being induced (Fig. 1; Dev. Comp. Immunol. 25 (2001) 841). Healthy fish exhibit both nonspecific and specific immune responses depending directly on environmental temperature. Pollution of the natural aquatic environment with industrial or agricultural sewage is an important immunosuppressing factor resulting in higher susceptibility to infectious diseases. To date, the possible immunotoxicity of a substance is evaluated using quantification of humoral factors like lysozyme, complement, C-reactive protein or total immunoglobulins but less often using functional assays. Furthermore, most of the functional assays (phagocytosis, respiratory burst, proliferative response) are based on the measurement of the response of resting but not of specific activated immune cells. However, the physiological responses of the immune system to an infection are based on a complex, stepwise activation and proliferation, especially of the specific immune functions after first contact to the microorganisms. In this report we describe in vitro methods for the evaluation of cellular immune functions of different leukocyte populations after specific in vivo triggering of the immune system. Parameters to be evaluated are activation and proliferation of leukocyte populations, phagocytosis and respiratory burst, secretion of antigen-specific antibodies and specific cell-mediated cytotoxicity. Furthermore, challenge models with bacterial (Aeromonas salmonicida) and viral pathogens (Viral Haemorrhagic Septicemia Virus, VHSV) are presented.

Effect of sulphadiazine and trimethoprim on the immune response of rainbow trout (Oncorhynchus mykiss)

A combination of sulphadiazine and trimethoprim at a ratio of 5:1 (SDZ/TMP) was tested for possible immunomodulatory effects. The aim of the study was to follow the immune response after vaccination with simultaneous drug treatment. The fish were immunised with a commercial oil-based divalent (furunculosis/vibriosis) vaccine and were simultaneously given oral drug treatment. The specific immune response was monitored by analysing the levels of specific antibodies with ELISA. As indicators of the nonspecific immune response, the lysozyme activity of serum was measured and the phagocytic activity of circulating leucocytes was monitored by a chemiluminescence assay. Total circulating leucocyte counts and differentials were also monitored. The disease resistance was evaluated by challenge tests at the end of the experiment. The results indicate that SDZ/TMP at a ratio of 5:1 does not interfere negatively with the immune response in rainbow trout after vaccination. A slight stimulation in the antibody response as well as in the chemiluminescence response of circulating granulocytes was recorded in fish treated with the drugs in connection with vaccination. The drugs did not significantly affect the survival after challenge.

The effect of dietary immunomodulation upon Edwardsiella tarda vaccination in healthy and immunocompromised Indian major carp (Labeo rohita)

In order to determine the impact on disease resistance of four dietary immunomodulators viz., beta-1,3 glucan, levamisole, vitamins C and E, in an important farmed Indian major carp species, rohu (Labeo rohita Ham.), fish were fed diets containing various levels of these substances during a 60 day trial. Aflatoxin B1 (AFB,) at 125 mg kg(-1) body weight was injected intraperitoneally (i.p.) into fish to induce an immunosuppressive state on the first day of the experiment in some individuals. The fish were vaccinated against formalin-killed Edwardsiella tarda vaccine on day 30 of the experiment. Specific immunity, as measured by bacterial agglutination titre and disease resistance against E. tarda, was determined at the end of the trial. The results demonstrate that all the four immunomodulators were capable of significantly (P<0.05) increasing specific immunity and reducing mortality in immunocompromised fish but failed to enhance specific immunity and protection in healthy fish. The increased bacterial agglutination titre by beta-1,3 glucan, and reduced mortality losses by both beta-1,3 glucan and levamisole were marked in healthy vaccinated fish compared with their controls. Similarly, all four substances significantly reduced the mortality rates in immunocompromised and healthy unvaccinated fish. Out of these four substances, glucan was recorded to be the most effective immunomodulator in rohu. The present results suggest that the introduction of these substances into the diet of fish grown in farms under immunosuppressive/stressful conditions could increase their resistance to infection by reducing mortality rates and offer economic benefits.

Effect of florfenicol on the immune response of rainbow trout (Oncorhynchus mykiss)

Florfenicol, a drug effective against several bacterial diseases of fish, was tested for possible immunomodulatory effects. The aim of the study was to follow the kinetics of the immune response after vaccination with simultaneous oral antibiotic treatment. The fish were immunised with a commercial oil-based divalent (furunculosis/vibriosis) vaccine and were simultaneously given oral antibiotic treatment. The specific immune response was monitored by analysing the levels of specific antibodies with ELISA. As an indicator of the non-specific immune response the phagocytic activity of circulating leucocytes was measured by a chemiluminescence assay. Total circulating leucocyte counts and differentials were also monitored. The disease resistance was evaluated by challenge tests at the end of the experiment. The results showed that florfenicol did not have any significant effect on antibody production and circulating leucocyte levels but caused a suppression in chemiluminescence response/phagocytic cell 5-6 weeks after vaccination. The survival after challenge was slightly suppressed by the florfenicol treatment. The RPS-value for the vaccinated group was 98% and for the florfenicol-treated group was 88%.

Influence of flumequine on in vivo mitogen responses of European eel (Anguilla anguilla L., 1758) lymphoid cells

The influence of flumequine on mitogen induced lymphoid cell proliferation in European eels (Anguilla anguilla L., 1758) was studied. For this purpose an in vivo test, using peroral drug administration followed by successive intraperitoneal injections with concanavalin A (ConA) or bacterial lipopolysaccharides (LPS) and 5-bromo-2'-deoxyuridine, was applied. Direct counting of proliferated cells in blood smears revealed that flumequine possesses mitogenic properties. A synergistic and an antagonistic effect of the drug was observed after LPS and ConA stimulation, respectively. Flow cytometric analysis of peripheral blood lymphoid cells showed a significant reduction of the mean proportion surface immunoglobulin positive cells in the flumequine-treated animals. It is concluded that flumequine enhances proliferation of lymphoid cells (probably surface immunoglobulin negative cells) in eel under the present experimental conditions.

Dietary intake of immunostimulants by rainbow trout affects non-specific immunity and protection against furunculosis

Immunostimulant preparations Macrogard, Candida utilis, Saccharomyces cerevisiae, Evetsel, Chitosan, or FinnStim were mixed into semipurified diets and fed to groups of rainbow trout for 1 week. Fish were bled by non-lethal caudal puncture and blood samples assayed for changes in non-specific cellular immunity and humoral protein levels. In the immunostimulated fish, hematocrit levels and lymphocyte counts remained relatively stable; however, elevations were observed in oxidative radical release, myeloperoxidase activity, phagocytic indexes, and potential killing activities of phagocytic cells including neutrophils. Total plasma protein and total immunoglobulin levels were elevated by the dietary immunostimulants. A challenge with the virulent pathogen that causes furunculosis, Aeromonas salmonicida, showed that the immunostimulated groups of fish were more resistant to the disease, confirming the potential use of these substances in fish culture for the prevention of disease.