Kim D. Thompson

Chinese herbs (Astragalus radix and Ganoderma lucidum) enhance immune response of carp, Cyprinus carpio, and protection against Aeromonas hydrophila

The effect of Chinese herbs (Astragalus radix and Ganoderma lucidum) on immune response of carp was investigated. Fish were fed diets containing Astragalus (0.5%), Ganoderma (0.5%) and combination of two herbs (Astragalus 0.5% and Ganoderma 0.5%) for 5 weeks. Other groups of fish were vaccinated (i.p.) against Aeromonas hydrophila/Aeromonas salmonicida (Shering Plough, Essex, U.K.) at the beginning of the experiment and fed the same diets as described above. Control fish (negative control) and fish vaccinated only (positive control) were fed basal diets without supplements of herbs. The respiratory burst activity, phagocytosis, lysozyme activity and circulatory antibody titres in plasma were monitored. Following 5 weeks after feeding, fish were infected with A. hydrophila and mortalities were recorded. The results of this study showed that feeding non-vaccinated and vaccinated carp with combination of Astragalus and Ganoderma stimulated respiratory burst activity, phagocytosis of phagocytic cells in blood and lysozyme and circulatory antibody titres in plasma in vaccinated carp. Fish challenged with A. hydrophila had variable survival. The best survival (60%) was in vaccinated group fed with both herbs, while almost 90% of control fish (negative control) and 60% of fish vaccinated only (positive control) died.

Immune responses of Nile tilapia (Oreochromis niloticus L.) clones: I. Non-specific responses.

The importance of genetic variation in the non-specific immune responses of Nile tilapia (Oreochromis niloticus L.) clones was investigated. Fully inbred clones (IC) of Nile tilapia, produced using gynogenesis and sex reversal, and crosses between these lines (outbred clones) were used in this study. Non-specific immune responses were compared between the ICs, including serum lysozyme activity and phagocytosis, and significant differences were observed between the different groups. Their natural resistance to Aeromonas hydrophila infection was also assessed by bacterial challenge. A positive correlation was observed between the level of infection obtained and the non-specific immune parameters measured. Cumulative mortalities of fish obtained in the study showed that when a IC susceptible to A. hydrophila was crossed with a resistant IC, the resulting progeny exhibited intermediate levels of resistance to that of their parents.

Survival and replication of Piscirickettsia salmonis in rainbow trout head kidney macrophages

Piscirickettsia salmonis is pathogenic for a variety of cultured marine fish species worldwide. The organism has been observed within host macrophages in natural disease outbreaks among coho salmon and European sea bass. In vitro studies, incorporating transmission electron microscopy (TEM) and ferritin loading of lysosomes, have confirmed that P. salmonis is capable of surviving and replicating in rainbow trout macrophages. Certain features of this intracellular survival underline its difference to other intracellular pathogens and suggest that a novel combination of defence mechanisms may be involved. Escape into the macrophage cytoplasm is not used as a means to avoid phago-lysosomal fusion and the organism remains at least partly enclosed within a vacuole membrane. While the piscirickettsial vacuole is often incomplete, survival and replication appear to require occupation of a complete, tightly-apposed, vacuolar membrane which does not fuse with lysosomes. Unlike some mammalian rickettsiae, actin-based motility (ABM) is not used as a means of intercellular spread. It is postulated that the presence of numerous small vesicles within vacuoles, and at gaps in the vacuolar membrane, may result from the blebbing of the piscirickettsial outer membrane seen early in the infection.

Immunostimulation of striped snakehead Channa striata against epizootic ulcerative syndrome

Abstract Five immunostimulants were injected intraperitoneally into striped snakeheads (Channa striata). The inhibitory effects of the serum and macrophages collected from the treated fish on the germination and subsequent growth of Aphanomyces invadans (=piscicida), the causative agent of epizootic ulcerative syndrome (EUS), were then assessed. Salar-bec, a vitamin premix, and Ergosan, an alginate, both stimulated the inhibitory effects of serum on the germination and subsequent growth of A. invadans cysts, and the inhibitory effect of macrophages on growth. Betamak C85, a yeast extract containing β glucans and mannans, and Lysoforte, a lysophospholipid biosurfactant, induced little or no improvement in the parameters measured. Oro glo layer dry, a xanthophyll preparation, was rejected because of high mortalities among injected fish. Salar-bec showed the greatest improvement in the inhibition of both germination and growth by serum, and of growth by macrophages. It was selected for a tank trial in which snakeheads were fed on pellets coated with 2 g kg−1 Salar-bec, then injected with A. invadans. Control fish were fed on uncoated feed. Although the incidence of infection was not affected, hyphae appeared later in treated fish and granulomata developed faster at the infection site, suggesting an enhanced ability to contain the infection. Relative percent survival of treated fish was 59.2% higher than the controls over the 40-day trial. Anti-A. invadans antibody concentration was higher in treated fish, which may also have contributed to the containment of the infection.

Understanding the interaction between Betanodavirus and its host for the development of prophylactic measures for viral encephalopathy and retinopathy

Over the last three decades, the causative agent of viral encephalopathy and retinopathy (VER) disease has become a serious problem of marine finfish aquaculture, and more recently the disease has also been associated with farmed freshwater fish. The virus has been classified as a Betanodavirus within the family Nodaviridae, and the fact that Betanodaviruses are known to affect more than 120 different farmed and wild fish and invertebrate species, highlights the risk that Betanodaviruses pose to global aquaculture production. Betanodaviruses have been clustered into four genotypes, based on the RNA sequence of the T4 variable region of their capsid protein, and are named after the fish species from which they were first derived i.e. Striped Jack nervous necrosis virus (SJNNV), Tiger puffer nervous necrosis virus (TPNNV), Barfin flounder nervous necrosis virus (BFNNV) and Red-spotted grouper nervous necrosis virus (RGNNV), while an additional genotype turbot betanodavirus strain (TNV) has also been proposed. However, these genotypes tend to be associated with a particular water temperature range rather than being species-specific. Larvae and juvenile fish are especially susceptible to VER, with up to 100% mortality resulting in these age groups during disease episodes, with vertical transmission of the virus increasing the disease problem in smaller fish. A number of vaccine preparations have been tested in the laboratory and in the field e.g. inactivated virus, recombinant proteins, virus-like particles and DNA based vaccines, and their efficacy, based on relative percentage survival, has ranged from medium to high levels of protection to little or no protection. Ultimately a combination of effective prophylactic measures, including vaccination, is needed to control VER, and should also target larvae and broodstock stages of production to help the industry deal with the problem of vertical transmission. As yet there are no commercial vaccines for VER and the aquaculture industry eagerly awaits such a product. In this review we provide an overview on the current state of knowledge of the disease, the pathogen, and interactions between betanodavirus and its host, to provide a greater understanding of the multiple factors involved in the disease process. Such knowledge is needed to develop effective methods for controlling VER in the field, to protect the various aquaculture species farmed globally from the different Betanodavirus genotypes to which they are susceptible.

The search for the IFN-γ receptor in fish: functional and expression analysis of putative binding and signalling chains in rainbow trout Oncorhynchus mykiss.

Interferons (IFNs), consisting of three major subfamilies, type I, type II (gamma) and type III (lambda) IFN, activate vertebrate antiviral defences once bound to their receptors. The three IFN subfamilies bind to different receptors, IFNAR1 and IFNAR2 for type I IFNs, IFNgammaR1 and IFNgammaR2 for type II IFN, and IL-28R1 and IL-10R2 for type III IFNs. In fish, although many types I and II IFN genes have been cloned, little is known about their receptors. In this report, two putative IFN-gamma receptor chains were identified and sequenced in rainbow trout (Oncorhynchus mykiss), and found to have many common characteristics with mammalian type II IFN receptor family members. The presented gene synteny analysis, phylogenetic tree analysis and ligand binding analysis all suggest that these molecules are the authentic IFNgammaRs in fish. They are widely expressed in tissues, with IFNgammaR1 typically more highly expressed than IFNgammaR2. Using the trout RTG-2 cell line it was possible to show that the individual chains could be differentially modulated, with rIFN-gamma and rIL-1beta down regulating IFNgammaR1 expression but up regulating IFNgammaR2 expression. Over-expression of the two receptor chains in RTG-2 cells revealed that the level of IFNgammaR2 transcript was crucial for responsiveness to rIFN-gamma, in terms of inducing gammaIP expression. Transfection experiments showed that the two putative receptors specifically bound to rIFN-gamma. These findings are discussed in the context of how the IFNgammaR may bind IFN-gamma in fish and the importance of the individual receptor chains to signal transduction.

Adhesion of the fish pathogen Flavobacterium psychrophilum to unfertilized eggs of rainbow trout (Oncorhynchus mykiss) and n-hexadecane

Aims: The ability of Flavobacterium psychrophilum, the causative agent of rainbow trout fry syndrome (RTFS) in fish, to attach to unfertilized rainbow trout (Oncorhynchus mykiss) eggs and to hydrocarbon n‐hexadecane was examined in the present study.

Immune Response of Rainbow Trout to Extracellular Products of Mycobacterium spp.

Abstract A primary intraperitoneal (IP) vaccination of extracellular products (ECP) from Mycobacterium spp. (strains TB40, TB267, or Mycobacterium marinum) mixed with Freunds incomplete adjuvant and followed by a secondary IP injection at 8 weeks resulted in the elevation of both the nonspecific and the specific immune responses of rainbow trout Oncorhynchus mykiss. Increased nitroblue tetrazolium and phagocytosis activity were observed in these fish; peaks in activity occurred at weeks 2 and 6 after primary immunization with a third peak at week 10. Lysozyme activity, on the other hand, peaked at weeks 2 and 8 after primary immunization except in the TB40-immunized group. A third peak of lysozyme activity was observed at week 10 after primary immunization. The activity of the specific immune response was monitored by an enzyme-linked immunosorbent assay and Western blot. The results indicate that antibodies to the ECP of Mycobacterium spp. were present in rainbow trout serum and that they reacted with m...

The effects of feeding immunostimulant β-glucan on the immune response of Pangasianodon hypophthalmus.

Immunostimulants are food additives used by the aquaculture industry to enhance the immune response of fish, and although β-glucans are now commonly used for this purpose in aquaculture, little is known about their effects on the immune response of Pangasianodon hypophthalmus. Thus, a variety of immune parameters (e.g. phagocytosis, respiratory burst, lysozyme, complement, peroxidase, total protein, total anti-protease, total IgM, natural antibody titres, and specific IgM titres) was examined in this species after feeding fish with a basal control diet or diets supplemented with 0.05, 0.1, or 0.2 g/kg fungal-derived β-glucan or 0.1% commercial yeast-derived β-glucan, as a positive control diet, for a period of four weeks. The effect of the glucans on disease resistance was then evaluated by experimentally infecting the fish with Edwardsiella ictaluri by immersion and mortalities monitored for 14 days. Samples were collected from fish for analysis at 0, 1, 3, 7, 14, 21 and 28 days post-feeding (dpf), and also at 14 days post infection (dpi). The lowest dose of fungal-derived β-glucan (0.05%) appeared insufficient to effectively stimulate the immune response of the fish, while those fed with the two highest levels of fungal-derived β-glucan had enhanced immune responses compared to the control group. Significantly elevated levels of respiratory burst activity on all days examined (P < 0.05) and lysozyme activity on 7 dpf were found in the group fed 0.2% fungal-derived β-glucan, while plasma anti-protease activity was significantly enhanced (P < 0.05) by 21 dpf, natural antibody titres by 3 dpf and complement activity by 7 dpf and also at 14 dpi in the group fed 0.1% fungal-derived β-glucan. No statistical differences was seen in the level of mortalities between the dietary groups, although the group fed with the control diet had the highest level of mortalities and the groups fed with commercial yeast-derived β-glucan and 0.2% fungal-derived β-glucan the lowest.

The influence of dietary β-glucans on the adaptive and innate immune responses of European sea bass (Dicentrarchus labrax) vaccinated against vibriosis

Abstract The effects of feeding 1,3/1,6 β-glucans on the innate and the adaptive immune responses of European sea bass (Dicentrarchus labrax) was investigated. Two experiments were carried out during the study. In the first, a number of non-specific immune parameters were examined at 4, 7, 10, 14, 21 and 25 days of feeding fish with a semipurified diet containing Macrogard ©, a commercially available form of 1,3/1,6 β-glucans. The respiratory burst activity of head kidney macrophages isolated from the different groups of fish fed the immunostimulant peaked and subsequently decreased at different times during the experiment. Head kidney macrophages from fish fed 250 ppm β-glucans had a statistically higher level of respiratory burst activity at Day 21 of feeding compared with fish fed no immunostimulant. No statistical differences were observed in lyzozyme activity during this trial. In the second experiment, the effect of feeding 1,3/1,6 β-glucans on the immune response of fish to an alginate-encapsulated Vibrio vaccine administered orally was examined. Respiratory burst of head kidney macrophages and serum lysozyme activity decreased in all fish over the course of the trial, while serum lysozyme activity was considerably lower than values obtained in the first experiment. Fish vaccinated orally had significant increases in antibody response by Week 2 post-vaccination, but β-glucans did not appear to affect these levels. Vaccination may have resulted in activating the immune system as a whole, thus masking any difference in immunostimulation by the β-glucans. It may be that the optimal doses and timing of β-glucans administration is different when the immunostimulant is administered alone or in combination with the vaccine. In conclusion, European sea bass can be immunomodulated with oral administration of β-glucan. Optimal doses and administration times have been established when β-glucans are fed alone, although further studies are needed to establish ideal feeding regimes for glucans administrated in combination with vaccination.