The effect of seasonality on normal haematological and innate immune parameters of rainbow trout Oncorhynchus mykiss L

Dietary administration of Bacillus amyloliquefaciens AV5 on antioxidant activity, blood parameters, and stress responses of Nile tilapia (Oreochromis niloticus) raised under hypoxia and temperature variability

The inability of Nile tilapia to tolerate hypoxia, as well as low and high temperatures, presents a significant economic concern, as it adversely affects their growth and leads to increased mortality rates. A 42-day feeding trial was conducted to evaluate the impact of adding Bacillus amyloliquefaciens AV5 to a fish meal on the physiological response of Nile tilapia. Three meals were administered to fish (23.4 ± 0.3g) in triplicates. The diets included GC (without B. amyloliquefaciens AV5), G1 (106cfu/g), and G2 (108cfu/g). After the treatment trial, we assessed the antioxidant parameters, hemato-immunological indices, and stress-related genes in O. niloticus. Subsequently, we subjected the fish to hypoxia for 20h and low and high temperatures for 3h each. The findings demonstrated a significant rise in white blood cells, red blood cells, haemoglobin, and hematocrit levels in the blood of fish that were fed a meal supplemented with B. amyloliquefaciens AV5, compared to the control group (GC) (P<0.05) and compared to the control group, the serum of all fish groups that were supplemented with B. amyloliquefaciens AV5 exhibited an increase in catalase, total antioxidant capacity and superoxide dismutase activity and a decrease in lactate dehydrogenase, alanine aminotransferase, aspartate aminotransferase, pyruvate kinase, myeloperoxidase, glucose, cortisol (P< 0.05). In addition, all fish diet groups that received B. amyloliquefaciens AV5 as a supplement exhibited elevated levels of HIF-1α and HSP70 expression in their livers (P<0.05). Nile tilapia in the G2 diet, exhibited improved values in most evaluated indices under various stress settings (P<0.05). These data indicate that the G2 supplement may be used as a preventive measure to weaken the impacts of environmental stress on O. niloticus.

Annual rhythm in immune functions of blood leucocytes in an ophidian, Natrix piscator

Annual variations in animal's physiological functions are an essential strategy to deal with seasonal challenges which also vary according to the time of year. Information regarding annual adaptations in the immune-competence to cope with seasonal stressors in reptiles is scarce. The present research plan was designed to analyze the presence of circannual immune rhythms in defense responses of the leucocytes in an ophidian, Natrix piscator. Peripheral blood leucocytes were obtained, counted, and superoxide anion production, neutrophil phagocytosis, and nitrite release were tested to assess the innate immune functions. Peripheral blood lymphocytes were separated by centrifugation (utilizing density gradient) and the cell proliferation was measured. The Cosinor rhythmometry disclosed the presence of significant annual rhythms in the number of leucocytes, superoxide anion production, nitric oxide production, and proliferation of stimulated lymphocytes. The authors found that respiratory burst activity and proliferative responses of lymphocytes were crucial immune responses that showed the annual rhythm. It was summarized that the immune function of the N. piscator is a labile attribute that makes the animal competent to cope with the seasonal stressor by adjustment in the potency of response.

Seasonal Immune Rhythms of head kidney and spleen cells in the freshwater Teleost, Channa punctatus

Annual rhythms in immune function are the reflection of a crucial physiological strategy to deal with environmental stressors. The fish are pivotal animal models to study the annual rhythm and to understand the evolution of the vertebrate biological system. The current research was planned to assess the annual changes in the innate immune functions of immune cells in a teleost, Channa punctatus. Head kidney and splenic macrophage phagocytosis, superoxide generation, and nitrite release were evaluated to assess innate immunity. Cell-mediated immunity was measured through head kidney and splenic lymphocyte proliferation in presence of mitogens. The superoxide anion generation by the cells of head kidney and spleen was maximum in October. A bimodal pattern in nitrite production was observed with the first peak in November and the second in March. Cosinor analysis revealed a statistically significant annual rhythm in nitrite production. Similarly, phagocytosis and lymphocyte proliferation also showed statistically significant annual rhythms. It was concluded that animals maintain an optimum immune response in seasonally changing environments. Elevated immunity during certain times of the year might assist animals deal with seasonal environmental stressors. Further research may be focused upon measuring survival rate and reproductive success after season induced elevated immunity.

Host-microbiota-parasite interactions in two wild sparid fish species, Diplodus annularis and Oblada melanura (Teleostei, Sparidae) over a year: a pilot study

BACKGROUND

The microbiota in fish external mucus is mainly known for having a role in homeostasis and protection against pathogens, but recent evidence suggests it is also involved in the host-specificity of some ectoparasites. In this study, we investigated the influence of seasonality and environmental factors on both fish external microbiota and monogenean gill ectoparasites abundance and diversity and assessed the level of covariations between monogenean and bacterial communities across seasons. To do so, we assessed skin and gill microbiota of two sparid species, Oblada melanura and Diplodus annularis, over a year and collected their specific monogenean ectoparasites belonging to the Lamellodiscus genus.

RESULTS

Our results revealed that diversity and structure of skin and gill mucus microbiota were strongly affected by seasonality, mainly by the variations of temperature, with specific fish-associated bacterial taxa for each season. The diversity and abundance of parasites were also influenced by seasonality, with the abundance of some Lamellodiscus species significantly correlated to temperature. Numerous positive and negative correlations between the abundance of given bacterial genera and Lamellodiscus species were observed throughout the year, suggesting their differential interaction across seasons.

CONCLUSIONS

The present study is one of the first to demonstrate the influence of seasonality and related abiotic factors on fish external microbiota over a year. We further identified potential interactions between gill microbiota and parasite occurrence in wild fish populations, improving current knowledge and understanding of the establishment of host-specificity.

Exploring gut microbiota in adult Atlantic salmon (Salmo salar L.): Associations with gut health and dietary prebiotics

BACKGROUND

The importance of the gut microbiota for physiological processes in mammals is well established, but the knowledge of their functional roles in fish is still limited. The aims of this study were to investigate associations between variation in taxonomical composition of the gut microbiota and gut health status in Atlantic salmon and to explore possible modulatory effects of dietary prebiotics in one net-pen farm in open water. The fish with initial mean body weight of around 240 g were fed diets based on the same basal composition, either without (Ref diet) or with (Test diet) yeast cell wall based-prebiotics, during the marine production phase from December to September the following year. Sampling was conducted at three sampling time points: January, April, and September, with average water temperature of 3.9 ℃, 3.4 ℃ and 9.6 ℃, respectively.

RESULTS

As the fish progressed towards September, growth, brush border membrane enzyme activities, and the expression in the gut of most of the observed genes involved in immune (e.g., il8, cd4a, myd88, il1b, gilt, tgfb, cd8b and cd3), barrier (e.g., zo1, occludin, ecad, claudin25b and claudin15), and metabolism increased significantly. Lipid accumulation in pyloric enterocytes decreased remarkably, suggesting improvement of gut health condition. The growth of the fish did not differ between dietary treatments. Further, dietary prebiotics affected the gut health only marginally regardless of duration of administration. Regarding gut microbiota composition, a decrease in alpha diversity (Observed species, Pielou and Shannon) over time was observed, which was significantly associated with an increase in the relative abundance of genus Mycoplasma and decrease in 32 different taxa in genus level including lactic acid bacteria (LAB), such as Lactobacillus, Leuconostoc, and Lactococcus. This indicates that developmental stage of Atlantic salmon is a determinant for microbial composition. Multivariate association analysis revealed that the relative abundance of Mycoplasma was positively correlated with gut barrier gene expression, negatively correlated with plasma glucose levels, and that its relative abundance slightly increased by exposure to prebiotics. Furthermore, certain LAB (e.g., Leuconostoc), belonging to the core microbiota, showed a negative development with time, and significant associations with plasma nutrients levels (e.g., triglyceride and cholesterol) and gene expression related to gut immune and barrier function.

CONCLUSIONS

As Atlantic salmon grew older under large-scale, commercial farm settings, the Mycoplasma became more prominent with a concomitant decline in LAB. Mycoplasma abundance correlated positively with time and gut barrier genes, while LAB abundance negatively correlated to time. Dietary prebiotics affected gut health status only marginally.

Temperature-associated virulence, species susceptibility and interspecies transmission of a Lactococcus petauri strain from rainbow trout

Lactococcus petauri is an important emergent aquaculture pathogen in the USA. To better understand environmental conditions conducive to piscine lactococcosis and the susceptibility of fish species, laboratory-controlled challenges were used as models of infection. Rainbow trout Oncorhynchus mykiss maintained at 13 or 18°C were challenged by intracoelomic (ICe) injection with 101, 103 or 105 colony-forming units per fish (CFU fish-1) and monitored for 21 d. At 13°C, trout experienced mortalities of 7, 7 and 0%, and bacterial persistence of 0, 20 and 0% in survivors, respectively. When exposed to the same bacterial doses, trout maintained at 18°C experienced mortalities of 59, 84 and 91%, and bacterial persistence of 60, 66 and 0% in survivors, confirming a significant role of temperature in the pathogenesis of lactococcosis. Additionally, the susceptibility of rainbow trout, Chinook salmon Oncorhynchus tshawytscha, white sturgeon Acipenser transmontanus, Nile tilapia Oreochromis niloticus, and koi Cyprinus carpio to infection by L. petauri was compared using ICe challenges at 18°C. Trout and salmon experienced 96 and 56% cumulative mortality, respectively, and 17% of surviving salmon remained persistently infected. There were no mortalities in the other fish species, and no culturable bacteria recovered at the end of the challenge. However, when surviving fish were used in further cohabitation trials, naïve trout housed with previously exposed tilapia exhibited 6% mortality, demonstrating that non-salmonids can become sub-clinical carriers of this pathogen. The data obtained provide useful information regarding temperature-associated virulence, fish species susceptibility, and potential carrier transmission of L. petauri that can be used in the development of better management practices to protect against piscine lactococcosis.

Effects of artificial photoperiods on antigen-dependent immune responses in rainbow trout (Oncorhynchus mykiss)

In this study, we investigated the effects of the artificial photoperiods that mimic summer (16L:8D) and winter (8L:16D) solstices, equinoxes (12L:12D), and the artificial 24-h light regimen (24L:0D) on the leukocyte populations and the T helper and regulatory type responses on rainbow trout (Oncorhynchus mykiss). Using flow cytometry analysis, we found that photoperiod induces changes in head kidney leukocyte subsets. The lymphoid subset increased in the 16L:8D summer solstice regime. The analysis using antibodies against B and T cells showed the increase of CD4-1⁺ T lymphocytes and other unidentified lymphoid cells, with no changes in the B cells. To investigate the modulatory influence of the photoperiod on the fish T cell response, we quantified in the head kidney the transcript levels of genes involved in the Th1 type response (t-bet, ifn-ƴ, il-12p35, il-12p40c), Th2 type response (gata3, il-4/13a), Th17 response (ror-ƴt, il-17a/f), T regulatory response (foxp3α, il-10a, tgf-β1), and the T cell growth factor il-2. The results showed that the seasonal photoperiod alone has a limited influence on the expression of these genes, as the only difference was observed in il-14/13a and il-10a transcripts of fish kept on the 16L:8D regimen. In addition, the 24L:0D treatment used in aquaculture produces a reduction of il-14/13a and il-17a/f. We also evaluated the effect of photoperiod in the presence of an antigenic stimulus. Thus, in fish immunized with the recombinant viral protein 1 (rVP1) of infectious pancreatic necrosis virus (IPNV), the photoperiod had a striking influence on the type of adaptive immune response. Each photoperiod fosters a unique immune signature of antigenic response. A classical type 1 response is observed in fish subjected to the 16D:8L photoperiod. In contrast, fish in the 12L:12D photoperiod showed only the upregulation of il-12p40c. Furthermore, none of the cytokines were increased in fish maintained on the artificial 24L:0D regimen, and a decrease in the master transcription factors (t-bet, ror-ƴt, and foxp3α) was observed. Thus, fish on the 12L:12D and 24L:0D photoperiod appear hyporesponsive regarding the T cell response. Altogether, this study showed that photoperiods modify the magnitude and quality of the T-helper response in rainbow trout and thus impact essential mechanisms for the generation of immune memory and protection against microorganisms.

Aloe vera reduces gut inflammation induced by soybean meal in Atlantic salmon (Salmo salar)

Plant-based protein sources, such as soybean, are widely used in fish nutrition due to their market availability, wide distribution and acceptable nutritional quality. However, in some fish species, soybean meal-based diets cause gut inflammation, decreasing both nutrient absorption and growth rates. A suitable alternative to avoid these problems could be the application of additives with anti-inflammatory activity to the diet. In this study, an Aloe vera (Aloe barbadensis Miller, AV) extract was analyzed as a dietary additive to reduce the gut inflammation in Atlantic salmon (Salmo salar) fed with soybean meal (SBM) diet. Fish were distributed in four duplicated groups and fed 28 days with fish meal control diet (FM), AV inclusion diet (AV), FM diet supplemented with AV (FM+AV), SBM diet to induce enteritis and SBM+AV. The fish gut response to these treatments was analyzed in distal intestine by histopathological scores, tissue morphometric measurements and immune gene expression parameters. The score results in fish fed with SBM-based diet clearly showed enteritis, meanwhile fish fed with AV supplemented diet significantly reduced the intestinal SBM signs of damage. These findings were associated to reduction of goblet cells number, lamina propria thickness and sub-epithelial mucosa size, with a significant decrease on pro-inflammatory cytokine il-1β to basal levels, similar to those present in fish fed FM diets. In conclusion, the administration of AV in salmon diet showed a protective intestinal activity against the detrimental effects of SBM, opening the possibility to improve its use as a feed additive in aquafeeds.

Seasonal immune rhythm of leukocytes in the freshwater snakehead fish, Channa punctatus

Annual rhythms are observed in many physiological processes and are an important approach to cope with seasonal stressors. The use of lower vertebrates as an experimental model is crucial to understand the evolution of this biological clock. This study aims to characterize the seasonal variability in the leukocyte immune responses in Channa punctatus. Leukocytes were harvested from peripheral blood and respiratory burst activity, leukocyte phagocytosis, and nitrite production were assessed to study innate immunity. Peripheral blood lymphocytes were segregated by centrifugation (density gradient) and proliferative responses of lymphocytes, in the presence of mitogens, were used to study cell-mediated immunity. Annual rhythms were validated in superoxide anion production, nitrite release and phagocytosis. Cosinor analysis revealed a differential pattern of lymphocyte proliferation which was dependent upon season and mitogen used. It was concluded that seasonal variation in immune activity might be associated with annual adaptation against diseases and the optimum immune status of seasonal breeders like fish helps them fight seasonal changes.

The role of sex, season and reproduction status on blood parameters in snow trout (Schizothorax labiatus) from River Jhelum, Kashmir, India

The current investigation was carried out with an aim to evaluate disparity in haematological and serum biochemical parameters of healthy male and female Schizothorax labiatus with respect to its four reproductive phases, i.e. preparatory (autumn), pre-spawning (winter), spawning (spring) and spent (summer). The study indicated that significant (p < 0.05) alterations were seen in gonadosomatic index (GSI) of S. labiatus with maximum value for both sexes noted in spring while minimum value in autumn. Contrary to this, the highest value of hepatosomatic index (HSI) for both sexes was noted in the autumn season and the lowest value in spring. The haemoglobin (Hb) content, red blood corpuscle (RBC) and white blood corpuscle (WBC) counts and haematocrit amount of S. labiatus also revealed significant (p < 0.05) variations with peak values noted in summer while least values were recorded during winter. It was also observed that male fishes comprised significantly (p < 0.05) maximum level of all these parameters amongst all seasons of the year, except WBC count. Erythrocyte indices specifically mean corpuscular haemoglobin (MCH), MCH concentration (MCHC) and mean corpuscular volume (MCV) exhibited insignificant (p > 0.05) alterations between the sexes. The lowest levels (p < 0.05) of serum glucose, cholesterol and urea were recorded in the pre-spawning period, i.e. winter, while as the highest values (p < 0.05) were seen in the summer because of the cessation of reproductive activities and greater availability of food. Similar trend was also noted in the amount of total protein, albumin and globulin of the fish, although insignificant (p > 0.05) variation was observed between sexes.

Seasonal Changes of Growth, Immune Parameters and Liver Function in Wild Chinese Sturgeons Under Indoor Conditions: Implication for Artificial Rearing

Seasonality has a significant effect on the physiology of fish, especially the effect of water temperature changes. In the present study, the growth, innate immune parameters and liver function indices of two rescued wild adult Chinese sturgeons under captive conditions were monitored for 1 year. The results showed that the total annual weight loss rate of the male was −4.58% and the total weight gain rate of the female was 24.12%, in which the weight of both individuals registered highly significant differences in summer, fall and winter (p < 0.01). The male Chinese sturgeon also exhibited negative specific growth rates (−0.1 to −0.8%) during spring to fall, whereas positive specific growth rates, ranging from 0.03 to 0.11%, were recorded in the female. Seasonality also affected the innate immune parameters of the two Chinese sturgeons, in which leukocytes had been increasing since spring and C-reactive protein (CRP) content was significantly higher (p < 0.05) in summer than fall in both individuals. The CRP level of the male Chinese sturgeon showed a significant increase from fall to winter (p < 0.05), suggesting that it may have contracted infection or inflammation during this study period. With the analysis of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), transaminase (AST:ALT) ratio, alkaline phosphatase, albumin to globulin ratio and triglycerides, it was found that the liver function of the captive Chinese sturgeons was adversely affected along seasonal changes, with the highest degree of liver impairment in winter. In combining observations from growth performance and changes in innate immune and liver function parameters, the present findings deduced that the male Chinese sturgeon under study was more susceptible to seasonal changes than the female. For better indoor culture of adult Chinese sturgeons, monitoring of hematological parameters to detect early signs of inflammation and liver function abnormality should be conducted with routine veterinary care during prolonged captivity.

Variations in Rainbow Trout Immune Responses against A. salmonicida: Evidence of an Internal Seasonal Clock in Oncorhynchus mykiss

In poikilothermic vertebrates, seasonality influences different immunological parameters such as leukocyte numbers, phagocytic activity, and antibody titers. This phenomenon has been described in different teleost species, with immunological parameters peaking during warmer months and decreased levels during winter. In this study, the cellular immune responses of rainbow trout (Oncorhynchus mykiss) kept under constant photoperiod and water temperature against intraperitoneally injected Aeromonas salmonicida during the summer and winter were investigated. The kinetics of different leukocyte subpopulations from peritoneal cavity, spleen, and head kidney in response to the bacteria was measured by flow cytometry. Furthermore, the kinetics of induced A. salmonicida-specific antibodies was evaluated by ELISA. Despite maintaining the photoperiod and water temperature as constant, different cell baselines were detected in all organs analyzed. During the winter months, B- and T-cell responses were decreased, contrary to what was observed during summer months. However, the specific antibody titers were similar between the two seasons. Natural antibodies, however, were greatly increased 12 h post-injection only during the wintertime. Altogether, our results suggest a bias toward innate immune responses and potential lymphoid immunosuppression in the wintertime in trout. These seasonal differences, despite photoperiod and water temperature being kept constant, suggest an internal inter-seasonal or circannual clock controlling the immune system and physiology of this teleost fish.

Characterization of digenetic trematodes infecting African catfish (Clarias gariepinus) based on integrated morphological, molecular, histopathological, and immunological examination

Parasitic infection may cause massive losses in Clarias gariepinus fries and fingerlings. Therefore, this study aimed to characterize the digenetic trematodes species (two adults' flukes and one metacercariae) infecting African catfish Clarias gariepinus, as well as their histopathological impacts on infected fish. The intestinal flukes were identified as Orientocreadium batrachoides and Masenia bangweulensis based on their morphological and molecular characteristics. Sequencing of their 28S (LSU rRNA) and 18S rRNA (SSU rRNA) genes confirmed that these trematodes belong to the families Orientocreadiidae and Cephalogonimidae, respectively. The metacercariae trematode infecting skin and muscles were only morphologically identified as Cyanodiplostomum sp. The gene expression levels of MHC II increased in naturally infected fish either with O. batrachoides or Cyanodiplostomum sp. alone, compared with uninfected catfish. In addition, lysozyme levels in individual fish serum increased in catfish infected either with O. batrachoides or Cyanodiplostomum sp. alone. Histopathological examination of the skin revealed embedded parasitic cysts that displaced tissue in the dermis. Surrounding tissues were infiltrated with melanomacrophages and displayed dermal edema. Histopathological analysis showed O. batrachoides or M. bangweulensis between the gastric folds of the stomach of infected catfish, causing infiltration of mononuclear inflammatory cells in the lamina propria.

Genome-wide analysis of Toll-like receptors in zebrafish and the effect of rearing temperature on the receptors in response to stimulated pathogen infection

Water temperature has a major influence on the host innate immune defence and the infectivity of pathogens in ectothermic teleosts. Toll-like receptors (TLRs) are the first and well-characterized innate immune receptors that are conserved in vertebrates. However, little is known about the effect of temperature variation on TLRs in fish species. In this study, we used adult zebrafish as a research model to investigate the effect of water temperature on TLRs. Whole genome searches identified 20 TLR homologue genes in zebrafish. Multiple sequence alignment and protein structure analysis revealed the conserved domains for these TLR proteins. To identify TLR genes related to temperature variation, TLR family genes from 12 species with different body temperatures were assigned to conduct phylogenetic analyses. Based on the phylogenetic relationships, TLR3, TLR4, TLR5 and TLR20~21 were selected as candidate genes. Immunostimulation data indicated that TLR3, TLR5, and TLR21 were more sensitive to temperature variation and their expression levels were affected in response to pathogen stimulation. Taken together, our results provide a new opportunity to understand the roles of temperature on host innate immune response in fishes and have broader implications for disease prevention in aquaculture.

Impact of chronic exposure of rainbow trout, Oncorhynchus mykiss, to low doses of glyphosate or glyphosate-based herbicides

Glyphosate is an herbicidal active substance (AS) entering in the composition of a large diversity of pesticide products (glyphosate-based herbicides; GBH) used in modern intensive agriculture. This compound has a favorable environmental safety profile but was suspected to induce deleterious effects in aquatic organisms, with a potential effect of some associated co-formulants. This study aimed to assess the impact of direct and chronic exposure to glyphosate on the health status of rainbow trout, Oncorhynchus mykiss. A total of 36 genitors were exposed daily for 10 months to a dose of glyphosate representative of environmental concentrations (around 1 μg L-1) using the AS alone or two GBHs formulations (i.e. Roundup Innovert® and Viaglif Jardin®) and findings were compared to an unexposed control group (n=12). The effects of chemical exposure on the reproductive capacities, hemato-immunologic functions, energetic metabolism, oxidative stress and specific biomarkers of exposure were analyzed over a period of 4 months covering spawning. A limited mortality between 15% and 30% specific to the spawning occurred under all conditions. No differences were observed in reproduction parameters i.e. mean weights, relative fertility and fecundity. Red blood cell count, hematocrit index, mean corpuscular volume and white blood cell counts were similar for all the sampling dates. Significant changes were observed two months before spawning with a 70% decrease of the proportion of macrophages in trout exposed to Viaglif only and a reduction of 35% of the phagocytic activity in fish exposed to the two GBHs. Trends towards lower levels of expression of tumor necrosis factor-α (between 38% and 66%) were detected one month after the spawning for all contaminated conditions but without being statistically significant. Biomarkers of exposure, i.e. acetylcholine esterase and carbonic anhydrase activities, were not impacted and none of the chemical contaminants disturbed the oxidative stress or metabolism parameters measured. These results suggest that a 10 months exposure of rainbow trout to a concentration of 1 μg L-1 of glyphosate administered using the pure active substance or two GBHs did not significantly modify their global health including during the spawning period. The immunological disturbances observed will need to be further explored because they could have a major impact in response to infectious stress.

Seasonal Temperature Fluctuations Differently Affect the Immune and Biochemical Parameters of Diploid and Triploid Oncorhynchus mykiss Cage-Cultured in Temperate Latitudes

In the coming decades, and despite advances in the selection of resistant strains and the production of triploid organisms, the temperature could seriously affect salmonid aquaculture. Lower environmental tolerance has been hinted at for triploids, but the physiological mechanisms leading to such differences, and whether they are translated to the individual level, are poorly understood. This study aimed to evaluate the effects of seasonal variations on the humoral and immune status in the blood (peripheral blood leukocytes) and plasma (antiprotease, lysozyme and peroxidase activities), the oxidative stress (catalase, glutathione-S-transferase, total glutathione and lipid peroxidation) balance in the liver, and the energy budget (sugars, lipids, proteins and energy production) in the liver and muscle of diploid and triploid Oncorhynchus mykiss. Leukocytes’ numbers changed with the water temperature and differed between fish ploidies. Peroxidase activity was increased in the summer, but lysozyme and antiprotease activities were increased in the winter. Concomitantly, antioxidant defenses were significantly altered seasonally, increasing oxidative damage at higher temperatures. Moreover, warmer waters induced a reduction in the energy production measured in the liver. Differences in feed efficiency, which have been previously reported, were confirmed by the low lipid and protein contents of the muscle of the triploids. In sum, the inherent trade-offs to deal with the seasonal changes culminated in the higher growth observed for diploid fish.

Can skyglow reduce nocturnal melatonin concentrations in Eurasian perch?

Artificial light at night (ALAN) changes the natural rhythm of light and darkness and can impair the biorhythms of animals, for example the nocturnal melatonin production of vertebrates, which serves as a proxy for daily physiological rhythms. Freshwater fish are exposed to ALAN in large urban and suburban areas in the form of direct light or in the form of skyglow, a diffuse brightening of the night sky through the scattered light reflected by clouds, atmospheric molecules, and particles in the air. However, investigations on the sensitivity of melatonin production of fish towards low intensities of ALAN in the range of typical skyglow are rare. Therefore, we exposed Eurasian perch (Perca fluviatilis) to nocturnal illumination levels of 0.01 lx, 0.1 lx and 1 lx and a control group with dark nights and daylight intensities of 2900 lx in all groups. After ten days of exposure to the experimental conditions, tank water was non-invasively sampled every 3 h over a 24 h period and melatonin was measured by ELISA. Melatonin was gradually reduced in all treatments with increasing intensity of ALAN whereas rhythmicity was maintained in all treatment groups although at 1 lx not all evaluated parameters confirmed rhythmicity. These results show a high sensitivity of Eurasian perch towards ALAN indicating that low light intensities of 0.01 lx and 0.1 lx as they occur in urban and suburban areas in the form of skyglow can affect the physiology of Eurasian perch. Furthermore, we highlight how this may impact perch in their sensitivity towards lunar rhythms and the role of skyglow for biorhythms of temperate freshwater fish.

Seasonal simulated photoperiods influence melatonin release and immune markers of pike perch Sander lucioperca

Melatonin is considered as the time-keeping hormone acting on important physiological functions of teleosts. While the influence of melatonin on reproduction and development is well described, its potential role on immune functions has little been considered. In order to better define an immune modulation by the melatonin hormone, we hypothesized that natural variations of photoperiod and subsequent changes in melatonin release profile may act on immune status of pikeperch. Therefore, we investigated during 70 days the effects of two photoperiod regimes simulating the fall and spring in western Europe, on pikeperch physiological and immune responses. Samples were collected at 04:00 and 15:00 at days 1, 37 and 70. Growth, plasma melatonin levels, innate immune markers and expression of immune-relevant genes in head kidney tissue were assessed. While growth and stress level were not affected by the seasonal simulated photoperiods, nocturnal levels of plasma melatonin were photoperiod-dependent. Innate immune markers, including lysozyme, complement, peroxidase and phagocytic activities, were stimulated by the fall-simulated photoperiod and a significant correlation was made with plasma melatonin. In addition to bring the first evidence of changes in fish immunocompetence related to photoperiod, our results provide an additional indication supporting the immunomodulatory action of melatonin in teleosts.

Seasonal changes of hydrolytic enzyme activities in the skin mucus of rainbow trout, Oncorhynchus mykiss at different body sizes

The innate immune factors in the skin mucus of fish are affected by the ecological and physiological conditions such as developmental stage and seasonal cycle. The aim of this study was to investigate the seasonal changes in soluble protein and the hydrolytic enzyme activities of the skin mucus of rainbow trout including lysozyme, alkaline phosphatase (ALP) and proteases at different body sizes. Skin mucus samples were collected over three consecutive season periods including winter, spring and late summer. In each season, sampling was performed separately from three different weight groups including 2-20 g (W1), 100-200 g (W2) and 400-600 g (W3) fish. Our results showed a significant increase of soluble protein in all three weight groups from winter to spring when water temperature elevated from 9 °C to 14 °C. Moreover lysozyme activity was remarkably elevated in W1 fish from winter to late summer. In all three seasons, the activity of lysozyme was significantly decreased along with increasing the fish size. Contrary to lysozyme, the activity of proteases and ALP showed a decreasing trend from winter to late summer. A significant positive correlation was found between the proteases and ALP activity, proposing that both proteases and ALP might have important synergic roles in the mucosal innate immune function of rainbow trout. Moreover, using reverse transcription PCR (RT-PCR) analysis of some proteases genes including cathepsin-L and cathepsin-D, we demonstrated that the proteases are transcribed and likely synthesized in epidermal mucus cells of rainbow trout. The present study confirmed seasonal changes of hydrolytic enzyme activities in the skin mucus of rainbow trout across all three weight groups, with the highest variation in juvenile fish.

Reliability evaluation of biomarker reference ranges for mesocosm and field conditions: Cellular innate immunomarkers in Gasterosteus aculeatus

Due to their sensitivity to environmental contamination and their link with fish health status, innate immunomarkers are of great interest for environmental risk assessment studies. Nevertheless, the lack of knowledge about the effect of confounding factors can lead to data misinterpretation and false diagnostics. So, the determination of reference values was of huge interest for the integration of biomarkers in biomonitoring programs. Laboratory immunomarker reference ranges (including cellular mortality, leucocyte distribution, phagocytosis activity, respiratory burst and lysosomal presence) that consider three confounding factors (season, sex and body size) were previously developed in three-spined stickleback, Gasterosteus aculeatus, from our husbandry. Usefulness of these reference ranges in biomonitoring programs depends on how they can be transposed to various experimental levels, such as mesocosm (outdoor artificial pond) and field conditions. Immunomarkers were therefore measured every 2 months over 1 year in one mesocosm and in one site assumed to uncontaminated (Houdancourt, field). Differences between immunomarker seasonal variations in mesocosm and field fish on one side and laboratory fish on the other side were quantified: in some cases, seasonal trends were not significant or did not differ between mesocosm and laboratory conditions, but overall, models developed based on data obtained in laboratory conditions were poorly predictive of data obtained in mesocosm or field conditions. To propose valuable field reference ranges, mesocosm and field data were integrated in innate immunomarker modelling in order to strengthen the knowledge on the effect of confounding factors. As in laboratory conditions, sex was overall a confounding factor only for necrotic cell percentage and granulocyte-macrophage distribution and size was a confounding factor only for cellular mortality, leucocyte distribution and phagocytosis activity. Confounding factors explained a large proportion of immunomarker variability in particular for phagocytosis activity and lysosomal presence. Further research is needed to test the field models in a biomonitoring program to compare the sensitivity of immunomarkers to the confounding factors identified in this study and the sensitivity to various levels of pollution.

Advances in salmonid fish immunology: A review of methods and techniques for lymphoid tissue and peripheral blood leucocyte isolation and application

Evaluating studies over the past almost 40 years, this review outlines the current knowledge and research gaps in the use of isolated leucocytes in salmonid immunology understanding. This contribution focuses on the techniques used to isolate salmonid immune cells and popular immunological assays. The paper also analyses the use of leucocytes to demonstrate immunomodulation following dietary manipulation, exposure to physical and chemical stressors, effects of pathogens and parasites, vaccine design and application strategies assessment. We also present findings on development of fish immune cell lines and their potential uses in aquaculture immunology. The review recovered 114 studies, where discontinuous density gradient centrifugation (DDGC) with Percoll density gradient was the most popular leucocyte isolation method. Fish head kidney (HK) and peripheral blood (PB) were the main sources of leucocytes, from rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Phagocytosis and respiratory burst were the most popular immunological assays. Studies used isolated leucocytes to demonstrate that dietary manipulations enhance fish immunity, while chemical and physical stressors suppress immunity. In addition, parasites, and microbial pathogens depress fish innate immunity and induce pro-inflammatory cytokine gene transcripts production, while vaccines enhance immunity. This review found 10 developed salmonid cell lines, mainly from S. salar and O. mykiss HK tissue, which require fish euthanisation to isolate. In the face of high costs involved with density gradient reagents, the application of hypotonic lysis in conjunction with mico-volume blood methods can potentially reduce research costs, time, and using nonlethal and ethically flexible approaches. Since the targeted literature review for this study retrieved no metabolomics study of leucocytes, indicates that this approach, together with traditional technics and novel flow cytometry could help open new opportunities for in vitro studies in aquaculture immunology and vaccinology.

Characterisation of Chinook salmon (Oncorhynchus tshawytscha) blood and validation of flow cytometry cell count and viability assay kit

New Zealand Chinook salmon (Oncorhynchus tshawytscha) industry has great potential for growth and expansion. While production is relatively free of health problems, there is limited literature on haematology, and immunological tools to safeguard against possible future health threats. The current study aim was to characterise New Zealand farmed O. tshawytscha peripheral blood cellular composition, develop a micro-volume method to isolate peripheral blood mononuclear cells (PBMCs) and validate a microcapillary flow cytometry assay kit for PBMC cell count and viability assessment. We used light microscopy to characterise peripheral blood and PBMC cellular composition in combination with a flow cytometer Sysmex XT 2000i Haematology Analyser. ImageJ version 1.52 was used for cell size characterisation of freshly stained blood. The stability of PBMCs stained with the Muse^® Cell Count and Viability Assay Kit and the Trypan blue assay stains were studied at 4 °C and 21 °C for 60 min; while the Muse^® Cell Count and Viability Assay Kit was validated against the Trypan blue assay haemocytometer chamber to assess PBMC count and viability. Findings showed that O. tshawytscha smolt yearlings had total blood cell counts in the range of 1.9-2.7 × 10⁶ μL^-1. Differential cell counts revealed five cell types, comprising 97.18% erythrocytes, 2.03% lymphocytes, 0.67% thrombocytes, 0.09% monocytes, and unquantifiable neutrophils. Using micro-volumes of blood and Lymphoprep™, we successfully isolated fish PBMCs. Significantly, stained PBMCs remained stable for up to 45 min at 4 °C and 21 °C; while validation of the Muse^® protocol showed that this microfluidic instrument delivered more accurate and precise viability results than the haemocytometer. The Muse^® protocol is rapid, easy to use, has quick calibration steps, and is suitable for field use to facilitate onsite sample processing. These findings pave the way for future assessments of fish health and in vitro immunological studies in O. tshawytscha.

Modelling the effect of season, sex, and body size on the three-spined stickleback, Gasterosteus aculeatus, cellular innate immunomarkers: A proposition of laboratory reference ranges

Innate immunomarkers reflect both environmental contamination and fish health status, providing useful information in environmental risk assessment studies. Nevertheless, the lack of knowledge about the effect of confounding factors can lead to data misinterpretation and false diagnoses. The aim of this study was to evaluate the impact of three confounding factors (season, sex and body size) on three-spined stickleback innate immunomarkers in laboratory conditions. Results shown strong seasonal variations in stickleback innate immunomarkers, with higher immune capacities in late winter-early spring and a disturbance during the spawning period in late spring-summer. Sex and body size had a season dependant effect on almost all tested immunomarkers. Reference ranges were established in laboratory-controlled conditions (i.e. laboratory reference ranges) and compared with data obtained from in vivo chemical expositions. The predictive power of the statistical model depended on the immunomarker, but the control data of the in vivo experiments, realized in same laboratory conditions, were globally well include in the laboratory reference ranges. Moreover, some statistical effects of the in vivo exposures were correlated with an augmentation of values outside the reference ranges, indicating a possible harmful effect for the organisms. As confounding factors influence is a major limit to integrate immunomarkers in biomonitoring programs, modelling their influence on studied parameter may help to better evaluated environmental contaminations.

Comparative ploidy response to experimental hydrogen peroxide exposure in Atlantic salmon (Salmo salar)

While research into the growth, survival, nutrition and, more recently, disease susceptibility of triploid Atlantic salmon has expanded, there remains an overall lack of studies assessing the response of triploids to chemical treatments. It is essential that the response of triploids to disease treatments be characterised to validate their suitability for commercial production. This study aimed to investigate and compare the stress and immune responses of triploid and diploid Atlantic salmon following an experimental treatment with hydrogen peroxide (H₂O₂). A dose response test was first undertaken to determine a suitable test dose for both diploid and triploid Atlantic salmon. Following this, diploids and triploids were exposed to H₂O₂ (1800 ppm) for 20 min, as per commercial practices, after which blood glucose and lactate, and plasma cortisol and lysozyme were measured, along with the expression of oxidative stress and immune-related genes. In the first 6 h post-exposure to H₂O₂, comparable mortalities occurred in both diploid and triploid Atlantic salmon. Cortisol, glucose and lactate were not significantly influenced by ploidy suggesting that, physiologically, triploid Atlantic salmon are able to cope with the stress associated with H₂O₂ exposure as well as their diploid counterparts. Exposure to H₂O₂ significantly elevated the expression of cat and sod2 in diploid livers and gr, il1β and crp/sap1b in diploid gills, while it significantly decreased the expression of saa5 and crp/sap1a in diploid gills. In triploids, the expression levels of cat, hsp70, sod1, saa5, crp/sap1a and crp/sap1b in liver was significantly higher in fish exposed to H₂O₂ compared to control fish. The expression of gr, sod1 and il1β in triploid gills was also elevated in response to H₂O₂ exposure. This study represents the first experimental evidence of the effects of H₂O₂ exposure on triploid Atlantic salmon and continues to support their application into commercial production.

Streptococcus agalactiae infection kills red tilapia with chronic Francisella noatunensis infection more rapidly than the fish without the infection

In this study we examined the effect that a Francisella noatunensis (Fno) infection had on hybrid red tilapia (Oreochromis niloticus × Oreochromis mossambicus) subsquently infected with Streptococcus agalactiae. A variety of hemato-immunological parameters (haematocrit, total red blood cell count, mean corpuscular volume, total white blood and differential cell counts, total plasma protein, plasma lysozyme and plasma peroxidase activities, and respiratory burst and phagocytic activities of head-kidney macrophages) were measured in hybrid red tilapia that had been previously exposed to an Fno outbreak in a tilapia grow-out farm. The head-kidneys of these apparently healthy survivors, when checked by PCR were found to be Fno-positive with hemato-immunological parameters that were similar to fish without an a priori infection. The only exception was the percentage lymphocyte count in the peripheral blood, which was slightly, but significantly, lower in the Fno-infected fish, compared to those without the infection. When experimentally infected with S. agalactiae, the Fno-infected fish died more rapidly and at a significantly higher rate than fish without the infection. During the challenge, the hemato-immunological parameters of both groups of fish were very similar, although the Fno-infected fish, challanged with S. agalactiae expressed significantly higher plasma lysozyme and peroxidase activities, and their head kidney macrophages had significantly higher respiratory burst activity compared to non-Fno-infected fish challanged with S. agalactiae. The only two parameters for which Fno-infected fish showed significantly lower expressions than that of their non-infected counterparts were haematocrit and total red blood cell count. The cause of the rapidity and higher rates of mortality observed in the Fno-infected fish when challenged with S. agalactiae is unknown; but it may be due to a reduced erythropoiesis capability within the head-kidney because of the presence of Fno.

Transchem project - Part I: Impact of long-term exposure to pendimethalin on the health status of rainbow trout (Oncorhynchus mykiss L.) genitors

Pendimethalin is a herbicide active substance commonly used in terrestrial agricultural systems and is thus detected at high concentrations in the surface water of several European countries. Previous studies reported several histopathological changes, enzymatic antioxidant modulation and immunity disturbance in fish exposed to this pesticide. The objective of this work was to investigate the direct effects of long-term exposure to environmental concentrations of pendimethalin over a period of 18 months in rainbow trout (Oncorhynchus mykiss) genitors. To do so, an experimental system consisting of eight similar 400 L tanks with a flow-through of fresh river water was used to perform daily chemical contamination. Fish were exposed to 850 ng/L for one hour and the pendimethalin concentration was then gradually diluted during the day to maintain optimal conditions for the fish throughout the experiment and to achieve a mean theoretical exposure level of around 100 ng L^-1 per day. Every November, males and females were stripped to collect eggs and sperm and two new first generations of offspring were obtained. Kinetic sampling revealed differences in immune system parameters and antioxidative defences in the contaminated trout compared to the controls, due to pesticide exposure combined with seasonal changes related to gamete maturation. Moreover, reproductive capacity was significantly affected by exposure to the herbicide; a time lag of more than five weeks was observed for egg maturation in contaminated females and high bioconcentrations of pendimethalin were measured in eggs and sperm. Chemical transfer from genitors to offspring via gametes may affect embryo development and negatively impact the early stages of development.

A comparison of disease susceptibility and innate immune response between diploid and triploid Atlantic salmon (Salmo salar) siblings following experimental infection with Neoparamoeba perurans, causative agent of amoebic gill disease

Few studies have focussed on the health and immunity of triploid Atlantic salmon and therefore much is still unknown about their response to commercially significant pathogens. This is important if triploid stocks are to be considered for full-scale commercial production. This study aimed to investigate and compare the response of triploid and diploid Atlantic salmon to an experimental challenge with Neoparamoeba perurans, causative agent of amoebic gill disease (AGD). This disease is economically significant for the aquaculture industry. The results indicated that ploidy had no significant effect on gross gill score or gill filaments affected, while infection and time had significant effects. Ploidy, infection and time did not affect complement or anti-protease activities. Ploidy had a significant effect on lysozyme activity at 21 days post-infection (while infection and time did not), although activity was within the ranges previously recorded for salmonids. Stock did not significantly affect any of the parameters measured. Based on the study results, it can be suggested that ploidy does not affect the manifestation or severity of AGD pathology or the serum innate immune response. Additionally, the serum immune response of diploid and triploid Atlantic salmon may not be significantly affected by amoebic gill disease.

Neuroendocrine-immune interaction: Evolutionarily conserved mechanisms that maintain allostasis in an ever-changing environment

It has now become accepted that the immune system and neuroendocrine system form an integrated part of our physiology. Immunological defense mechanisms act in concert with physiological processes like growth and reproduction, energy intake and metabolism, as well as neuronal development. Not only are psychological and environmental stressors communicated to the immune system, but also, vice versa, the immune response and adaptation to a current pathogen challenge are communicated to the entire body, including the brain, to evoke adaptive responses (e.g., fever, sickness behavior) that ensure allocation of energy to fight the pathogen. This phenomenon is evolutionarily conserved. Hence it is both interesting and important to consider the evolutionary history of this bi-directional neuroendocrine-immune communication to reveal phylogenetically ancient or relatively recently acquired mechanisms. Indeed, such considerations have already disclosed an extensive "common vocabulary" of information pathways as well as molecules and their receptors used by both the neuroendocrine and immune systems. This review focuses on the principal mechanisms of bi-directional communication and the evidence for evolutionary conservation of the important physiological pathways involved.

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

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

Seasonal changes in immune parameters of rainbow trout (Oncorhynchus mykiss), brook trout (Salvelinus fontinalis) and brook trout × Arctic charr hybrids (Salvelinus fontinalis × Salvelinus alpinus alpinus)

Despite the high number of studies concerning seasonality of immune response in fish, information for some fish species is still scarce. Here, we assess seasonal changes in leukocyte counts and several immune parameters in three groups of farmed salmonids, i.e. brook trout (Salvelinus fontinalis), brook trout x Arctic charr hybrids (Salvelinus fontinalis x Salvelinus alpinus alpinus) and rainbow trout (Oncorhynchus mykiss) reared under the same conditions and fed with the same feed. Fish were sampled in five periods of the year (late April, early July, late August, early November and early February) and leukocyte counts, respiratory burst of blood phagocytes, lysozyme concentration in skin mucus and total complement activity were measured. Generalized linear models using fish body length as a continuous predictor and sampling period and fish species as categorical predictors, were significant for each of the parameters analysed. The highest seasonal variations in measured parameters were found in rainbow trout and lowest in hybrids. Our results confirm that measures of innate and adaptive immunity are strongly affected by season in all three groups of salmonids. The results will contribute to the improved assessment of immunocompetence in farmed fishes, essential for future sustainable development in aquaculture.

A comparison of the response of diploid and triploid Atlantic salmon (Salmo salar) siblings to a commercial furunculosis vaccine and subsequent experimental infection with Aeromonas salmonicida

Sterile triploid fish represent a solution to the problems associated with sexual maturation and escapees in aquaculture. However, as disease outbreaks continue to cause significant economic losses to the industry, it is essential that the response of triploids to disease and disease treatments be characterised. The aim of this study was to compare the response of triploid Atlantic salmon to a commercial furunculosis vaccine with that of diploid fish, and to assess the vaccine efficacy in the two ploidies through an experimental infection with Aeromonas salmonicida. Diploid and triploid Atlantic salmon were injected intraperitoneally with either phosphate buffered saline, liquid paraffin adjuvant or a commercial furunculosis vaccine. Following vaccination, growth, adhesion scores and a variety of assays to assess immune function, such as respiratory burst and antibody response, were measured. Vaccination did not have a significant effect on the weight of either ploidy prior to challenge at 750° days. Adhesion scores were significantly higher in vaccinated fish compared to unvaccinated fish, although no effect of ploidy was observed. Ploidy significantly affected respiratory burst activity following vaccination, however, with triploids exhibiting higher activity than diploids. Combined with lower white blood cell numbers observed in the triploids, it may be that this low cell number is compensated for by increased cellular activity. Ploidy however, did not have a significant effect on complement activity or antibody response, with significantly higher antibody levels detected in all vaccinated fish compared to unvaccinated controls. In addition, both ploidy groups were well protected following challenge with no difference in the relative percentage survival. Based on these results, it appears that ploidy does not affect the severity of adhesions that result post-vaccinate or in the fish's immune response following vaccination, and the furunculosis vaccine performs equally well in both diploid and triploid Atlantic salmon.

Fish Hematology and Associated Disorders

Fish health is a growing concern as pets, education, and aquaculture evolves. For the veterinary staff, fish handling, diagnostics, medicine, and surgery may require specialized training and equipment in comparison with terrestrial and arboreal animals, simply because of their aquatic nature and diversity. Fish hematology is one diagnostic tool that may not require additional equipment, may be inexpensive, and provide useful information in guiding treatment options. Challenges involving hematology may include handling and restraint, venipuncture, evaluation, and interpretation. In this article, strategies for these challenges are discussed for teleost (bony fish) and elasmobranch (cartilaginous fish) fish types.

Thymol and Carvacrol Affect Hybrid Tilapia through the Combination of Direct Stimulation and an Intestinal Microbiota-Mediated Effect: Insights from a Germ-Free Zebrafish Model

BACKGROUND

Essential oils (EOs) are commonly used as animal feed additives. Information is lacking on the mechanisms driving the beneficial effects of EOs in animals, especially the role played by the intestinal microbiota of the host.

OBJECTIVE

The purpose of this study was to clarify the relative contribution of direct effects of EOs on the physiology and immune system of tilapia and indirect effects mediated by the intestinal microbiota by using a germ-free zebrafish model.

METHODS

Juvenile hybrid tilapia were fed a control diet or 1 of 4 treatment diets containing 60-800 mg Next Enhance 150 (NE) (an EO product containing equal levels of thymol and carvacrol)/kg for 6 wk. The key humoral and cellular innate immune parameters were evaluated after the feeding period. In another experiment, the gut microbiota of tilapia fed a control or an NE diet (200 mg/kg) for 2 wk were transferred to 3-d postfertilization (dpf) germ-free (GF) zebrafish, and the expression of genes involved in innate immunity and tight junctions was evaluated in zebrafish at 6 dpf. Lastly, NE was directly applied to 3-dpf GF zebrafish at 3 doses ranging from 0.2 to 20 mg/L, and the direct effect of NE on zebrafish was evaluated after 1 and 3 d.

RESULTS

NE supplementation at 200 mg/kg enhanced phagocytosis activity of head kidney macrophages (×1.36) (P < 0.05) and plasma lysozyme activity (×1.69) of tilapia compared with the control (P < 0.001), indicating an immunostimulatory effect. Compared with those colonized with control microbiota, GF zebrafish colonized with NE microbiota showed attenuated induction of immune response marker genes serum amyloid a (Saa; ×0.62), interleukin 1β (Il1β; ×0.29), and interleukin 8 (Il8; ×0.62) (P < 0.05). NE treatment of GF zebrafish at 2 and 20 mg/L for 1 d upregulated the expression of Il1β (×2.44) and Claudin1 (×1.38), respectively (P < 0.05), whereas at day 3 the expression of Occludin2 was higher (×3.30) in the 0.2-mg NE/L group compared with the GF control (P < 0.05).

CONCLUSION

NE may affect the immunity of tilapia through a combination of factors, i.e., primarily through a direct effect on host tissue (immune-stimulating) but also an indirect effect mediated by microbial changes (immune-relieving).

A role for melatonin in maintaining the pro- and anti-inflammatory balance by influencing leukocyte migration and apoptosis in carp

Melatonin is responsible for the synchronization of many physiological processes, including the immune response. Here we focus on the expression of melatonin MT1 receptors in/on leukocytes, and on the effects of melatonin administration on the inflammatory processes of carp. For the first time, we showed that fish leukocytes express MT1 receptors, implicating direct responsiveness to melatonin stimulation. Moreover, both in vitro and in vivo, melatonin modulated the immune response. The most potent effects of melatonin concerned the regulation of leukocyte migration. Melatonin reduced chemotaxis of leukocytes towards CXC chemokines in vitro. In vivo, during zymosan induced peritonitis, i.p. administration of melatonin reduced the number of neutrophils. This correlated with a melatonin-induced decrease of gene expression of the CXCa chemokine. Moreover, melatonin induced a decrease of the respiratory burst in inflammatory leukocytes. Although these data do suggest a potent anti-inflammatory function for this hormone, melatonin-induced inhibition of leukocyte apoptosis clearly indicates towards a dual function. These results show that also in carp, melatonin performs a pleiotropic and extra-pineal function that is important in maintaining the delicate pro- and anti-inflammatory balance during infection. They furthermore demonstrate that neuroendocrine-immune interaction via melatonin is evolutionary conserved.

Recommendations to design environmental monitoring in the European bullhead, Cottus sp., based on reproductive cycle and immunomarker measurement

European bullhead is a relevant fish species to assess adverse effects of environmental stress on wild fish. Nevertheless, their complex reproductive cycle is very different between sites and could interfere with many physiological processes. Thus, prior to use biomarker to statute on environmental quality of rivers, we wanted to characterize reproductive profile (spawn number, GSI, gonad development). The major results demonstrated that the two types of reproductive cycle shown were strongly correlated to water temperature variation. In a second time, even if innate immunomarkers are highly relevant on biomonitoring program, hormonal variation seems to impact severely their responses. Thus, the link between reproductive status and immune activity (leucocyte distribution, cellular mortality, respiratory burst, phagocytosis activity) must also be study. Nonetheless, in the present work, immune capacities seems to be more correlated with season and environmental factors than reproduction.

Space-time modelling of the spread of pancreas disease (PD) within and between Norwegian marine salmonid farms

Infectious diseases are a constant threat to industrialised farming, which is characterised by high densities of farms and farm animals. Several mathematical and statistical models on spatio-temporal dynamics of infectious diseases in various farmed host populations have been developed during the last decades. Here we present a spatio-temporal stochastic model for the spread of a disease between and within aquaculture farms. The spread between farms is divided into several transmission pathways, including (i) distance related spread and (ii) other types of contagious contacts. The within-farm infection dynamics is modelled by a susceptible-infected-recovered (SIR) model. We apply this framework to model the spread of pancreas disease (PD) in salmon farming, using data covering all farms producing salmonids over 9 years in Norway. The motivation for the study was partly to unravel the spatio-temporal dynamics of PD in salmon farming and partly to use the model for scenario simulation of PD control strategies. We find, for example, that within-farm infection dynamics vary with season and we provide estimates of the timing from unobserved infection events to disease outbreaks on farms are detected. The simulations suggest that if a strategy involving culling of infectious cohorts is implemented, the number of detected disease outbreaks per year may be reduced by 57% after the full effect has been reached. We argue that the high detail and coverage of data on salmonid production and disease occurrence should encourage the use of simulation modelling as a means of testing effects of extensive control measures before they are implemented in the salmon farming industry.

Fish hematology and associated disorders

Fish health is a growing concern as pets, education, and aquaculture evolves. For the veterinary staff, fish handling, diagnostics, medicine, and surgery may require specialized training and equipment in comparison with terrestrial and arboreal animals, simply because of their aquatic nature and diversity. Fish hematology is one diagnostic tool that may not require additional equipment, may be inexpensive, and provide useful information in guiding treatment options. Challenges involving hematology may include handling and restraint, venipuncture, evaluation, and interpretation. In this article, strategies for these challenges are discussed for teleost (bony fish) and elasmobranch (cartilaginous fish) fish types.

Optimisation and standardisation of functional immune assays for striped catfish (Pangasianodon hypophthalmus) to compare their immune response to live and heat killed Aeromonas hydrophila as models of infection and vaccination

Aquaculture production of Pangasianodon hypophthalmus is growing rapidly in South East Asia, especially in Vietnam. As it is a relatively new aquaculture species there are few reports evaluating its immune response to pathogens. Thus, functional assays for P. hypophthalmus were optimised to evaluate both innate and adaptive immune responses, and were then used to examine immune response following stimulation with live and heat-killed Aeromonas hydrophila. These were used as models of infection and vaccination, respectively. Four treatment groups were used, including a control group, a group injected intraperitonally (IP) with adjuvant only, a group injected with heat-killed A. hydrophila (1 × 10(9) cfu ml(-1) mixed with adjuvant), and a group injected with a subclinical dose of live A. hydrophila. Samples were collected at 0, 1, 3, 7, 14 and 21 days post-injection (d.p.i.) to assess their immune response. The results indicated that challenge with live or dead bacteria stimulated the immune response in P. hypophthalmus significantly above the levels observed in control groups with respect to specific antibody titre, plasma lysozyme and peroxidase activity, and phagocytosis by head kidney macrophages at 7 or/and 14 d.p.i. At 21 d.p.i., total and specific antibody (IgM) levels and plasma lysozyme activity in fish injected with either live or dead A. hydrophila were significantly different to the control groups. Differential immune responses were observed between fish injected with either live or dead bacteria, with live A. hydrophila significantly stimulating an increase in WBC counts and plasma peroxidase activity at 3 d.p.i., with the greatest increase in WBC counts noted at 21 d.p.i. and in phagocytosis at 14 d.p.i. By 21 d.p.i. only the macrophages from fish injected with dead A. hydrophila showed significantly stimulation in their respiratory burst activity. This study provides basic information on the immune response in pangasius catfish that can be useful in the health control of this species.

Detection and quantification of Flavobacterium psychrophilum in water and fish tissue samples by quantitative real time PCR

Background

Flavobacterium psychrophilum is the agent of Bacterial Cold Water Disease and Rainbow Trout Fry Syndrome, two diseases leading to high mortality. Pathogen detection is mainly carried out using cultures and more rapid and sensitive methods are needed.

Results

We describe a qPCR technique based on the single copy gene β’ DNA-dependent RNA polymerase (rpoC). Its detection limit was 20 gene copies and the quantification limit 10³ gene copies per reaction. Tests on spiked spleens with known concentrations of F. psychrophilum (10⁶ to 10¹ cells per reaction) showed no cross-reactions between the spleen tissue and the primers and probe. Screening of water samples and spleens from symptomless and infected fishes indicated that the pathogen was already present before the outbreaks, but F. psychrophilum was only quantifiable in spleens from diseased fishes.

Conclusions

This qPCR can be used as a highly sensitive and specific method to detect F. psychrophilum in different sample types without the need for culturing. qPCR allows a reliable detection and quantification of F. psychrophilum in samples with low pathogen densities. Quantitative data on F. psychrophilum abundance could be useful to investigate risk factors linked to infections and also as early warning system prior to potential devastating outbreak.

Effects of sex and season in haematological parameters and cellular composition of spleen and head kidney of pejerrey (Odontesthes bonariensis)

Phylogenetic diversity in fish determines high interspecific variability in morphology as well as in physiological parameters. Moreover, several haematological variables and the organ composition of haemolymphopoietic sites may vary according to sex or season. The aim of this study was to establish the haematological parameters and the cellular composition of haemolymphopoietic organs in Odontesthes bonariensis, a commercially valuable fish species in Argentina, and also to determine gender or seasonal variations. Haematocrit exhibited the highest value in summer, while haemoglobin concentration was greater in summer and autumn. Erythrocyte count was higher in spring than autumn and winter, but did not differ with summer. The increase in these variables in seasons with higher water temperatures might be a compensatory mechanism to compensate the lower level of oxygen in the environment. Leucocyte formula and blast haemolymphopoietic cells in spleen and head kidney also showed annual variations since cells related to specific immune response, i.e., lymphocytes and thrombocytes, decrease in winter, whereas cells of the non-specific immune pathways, such as granulocyte, rise. The elevation of a particular type of circulating leucocyte was preceded by an increase in values of its precursor in blood in the previous season. Both, spleen and head kidney were active in haemolymphopoiesis, although with some differences in their activity during different seasons. Males showed higher values of circulating lymphoblasts and granulocytes than females, whereas females exhibited higher values of thrombocytes. This study corroborates the high interspecific variations in haematological parameters in fish that underlines the needing of basic studies in order to assess fish health status in new promising species for aquaculture.

Protective effect of hydroferrate fluid, MRN-100, against lethality and hematopoietic tissue damage in γ-radiated Nile tilapia, Oreochromis niloticus

Hydroferrate fluid, MRN-100, an iron-based compound derived from bivalent and trivalent ferrates, is a potent antioxidant compound. Therefore, we examined the protective effect of MRN-100 against γ-radiation-induced lethality and damage to hematopoietic tissues in fish. A total of 216 Nile tilapia fish (Oreochromis niloticus) were randomly divided into four groups. Group 1 served as a control that was administered no radiation and no MRN-100 treatment. Group 2 was exposed only to γ-radiation (15 Gy). Groups 3 and 4 were pre-treated with MRN-100 at doses of either 1 ml/l or 3 ml/l in water for 1 week, and subsequently exposed to radiation while continuing to receive MRN-100 for 27 days. The survival rate was measured, and biochemical and histopathological analyses of hematopoietic tissues were performed for the different treatment groups at 1 and 4 weeks post-radiation. Exposure to radiation reduced the survival rate to 27.7%, while treatment with MRN-100 maintained the survival rate at 87.2%. In addition, fish exposed to γ-radiation for 1 week showed a significant decrease in the total number of white blood cells (WBCs) and red blood cells (RBCs) series. However, treatment with MRN-100 protected the total WBC count and the RBCs series when compared with irradiated fish. Furthermore, significant histological lesions were observed in the hepatopancreas, spleen and gills of irradiated fish. However, treatment with MRN-100 protected the histopathology of various organs. We conclude that MRN-100 is a radioprotective agent in fish and may be useful as an adjuvant treatment to counteract the adverse side effects associated with radiation exposure.

Influence of melatonin on the immune system of fish: a review

Endocrine-immune system interactions have been widely demonstrated in mammals, whereas in fish, these relationships remain unclear. Of the organs that constitute the endocrine system, the pineal gland and its secretory product melatonin act in the synchronization of daily and seasonal rhythms in most vertebrates, including fish. Seasonal differences in immunocompetence and disease prevalence have been well documented in humans. Seasonality also strongly influences the life history of fish by controlling the timing of physiological events, such as reproduction, food intake, locomotor activity, and growth performance. Apart from its synchronizing capabilities, the role of melatonin in physiological processes in fish is not thoroughly understood. The purpose of this review is to summarize current studies on the effects of melatonin on the fish immune system. These studies suggest that melatonin represents an important component of fish endocrine-immune system interactions. The elucidation of the defense mechanisms of fish will facilitate the development of health management tools to support the growing finfish aquaculture industry as well as address questions concerning the origins and evolution of the immune system in vertebrates.

Interacting effects of water temperature and dietary protein level on hematological parameters in Nile tilapia juveniles, Oreochromis niloticus (L.) and mortality under Streptococcus iniae infection

Based on central composite rotatable experimental design and response surface method, the interacting effects of temperature (20 °C-34 °C) and dietary protein level (25%-50%) on hematological parameters including red blood cell (RBC), white blood cell (WBC) and hemoglobin (Hb) of juvenile Oreochromis niloticus were studied under laboratory conditions. The experiment lasted for 7 weeks. After the feeding trial, fish were challenged with Streptococcus iniae and mortality was recorded for within 8 days. Results showed that the linear and quadratic effects of temperature on RBC, WBC and Hb were highly significant (P < 0.01). When the dietary protein level was 25%-50%, the RBC, WBC and Hb were increased firstly and then decreased, but the linear and quadratic effects of protein level were insignificant (P > 0.05). The interacting effects of temperature and protein level on RBC and Hb were significant (P < 0.05). The regression equations of RBC, WBC and Hb toward the two factors of interest were established, with the coefficients of determination being 0.870, 0.836 and 0.881, respectively (P < 0.01). These equations could be used for prediction in practice. After the challenge, the mortalities for the combinations of 22.1 °C/28.7% and 20.0 °C/37.5% were significantly higher than 27.0 °C/37.5% (P < 0.05). The optimal temperature/dietary protein level combination was obtained at 27.9 °C/38.1% at which the lowest mortality (13.76%) was attained. This value was close to the optimal temperature/dietary protein level combination (29.4 °C/41.9%) for the greatest levels of RBC (2.560 × 10(6) μL(-1)), WBC (270.648 × 10(3) μL(-1)) and Hb (92.851 g L(-1)). The results of this study indicated that preferred temperature/dietary protein level combination might strengthen the non-specific immunity and reduce susceptibility to S. iniae.

Pseudomonas M162 confers protection against rainbow trout fry syndrome by stimulating immunity

AIMS

  To evaluate the antagonistic effect of Pseudomonas M162 against Flavobacterium psychrophilum.

METHODS AND RESULTS

  The antagonistic activity of M162 was tested in vivo and in vitro, and its mode of action examined by siderophore production and immunological responses of rainbow trout (Oncorhynchus mykiss) fry. Pseudomonas M162 inhibited the growth of Fl. psychrophilum in vitro and increased the resistance of the fish against the pathogen, resulting in a relative per cent survival (RPS) of 39·2%. However, the siderophores produced by M162 did not have an inhibitory effect on Fl. psychrophilum. In fish fed with M162, the probiotic colonized the gastrointestinal tract and stimulated peripheral blood leucocyte counts, serum lysozyme activity and total serum immunoglobulin levels after 3 weeks from the start of feeding.

CONCLUSIONS

  This study showed the potential of Pseudomonas M162 as a probiotic by reducing the mortalities that occurred during an experimental Fl. psychrophilum infection, resulting mainly through the immunostimulatory effects of the bacterium.

SIGNIFICANCE AND IMPACT OF THE STUDY

  Rainbow trout fry syndrome (RTFS) causes high mortalities during the early life stages of the fish's life cycle, partly because their adaptive immunity has not yet fully developed. Thus, immunomodulation by probiotics could be an effective prophylactic method against RTFS.