Modulation of stress and innate immune response by corticosteroids in pacu (Piaractus mesopotamicus).

Understanding how stress and corticosteroid modulates the innate immune response is one of the keys to improving productivity and reducing losses in intensive aquaculture. Thus, we investigated the effects of dietary corticosteroids (7 days; long-term exposure) and transport (4 h; short-term stress) on stress and innate immune response in pacu. For this end, fish were fed with diets containing dexamethasone (100 mg kg-1) or hydrocortisone (200 mg kg-1), followed by transport, and then were intraperitoneally inoculated with heat-killed Aeromonas hydrophila or PBS (sham-inoculation). Fish were sampled after a 7-day feeding period, immediately post-transport and 24 h post-transport and inoculation. The dietary treatment of corticosteroids decreased resting cortisol levels by inhibiting the production of cortisol on the hypothalamus pituitary interrenal-axis. Further, both corticosteroids reduced hematocrit, red blood cells, haemoglobin and hemolytic activity of the complement, while they increased glucose levels and serum lysozyme concentrations. The transport increased cortisol and glucose levels and reduced the humoral immune defenses such as serum lysozyme concentration and hemolytic activity of the complement system. Interestingly, the hemolytic activity of the complement system increased sharply in fish fed with corticosteroids immediately post-transport, when they had their HPI-axis partially suppressed by the corticosteroids. This finding suggests a stimulatory effect of the catecholamines released during the transport on the activity of the complement system. Our results are highly valuable to understanding the stress and innate immune responses to long-term exposure to corticosteroids and short-term stress in fish and may provide insights into how corticosteroids modulate the innate immune system.

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

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

ß-Glucan-induced cortisol levels improve the early immune response in matrinxã (Brycon amazonicus).

This study investigated the role of endogenous cortisol on the innate immune response in matrinxã (Brycon amazonicus) fed with ß-glucan, prior to and after stressor exposure and bacterial challenge. For this, we evaluated the serum cortisol and plasma glucose levels, the serum lysozyme levels, the hemolytic activity of the complement system, and the respiratory activity of leukocytes, as well as the number of circulating erythrocytes and leukocytes of fish fed during 15 days with diets containing ß-glucan 0.1% (ß-G) or ß-glucan 0.1% + metyrapone 30 mg kg-1 fish (ß-G + MTP). Dietary MTP was used to block cortisol production. After feeding, fish were air-exposed during 3 min, to endogenously increase the cortisol levels. Following that, they were challenged with intraperitoneal injection of Aeromonas hydrophila. Results were compared with a positive control group fed with a ß-glucan-free diet. A negative control group, also fed with ß-glucan-free diet but inoculated with PBS, was established to evaluate the effect of the handling during injection. Fish were sampled prior to the stressor exposure, 30 min after exposure, and 24 h post infection (hpi). Herein we observed that dietary ß-G modulated the cortisol profile prior to and after the stressor, increasing the number and activity of leukocytes. Moreover, cortisol showed to be an efficient modulator of both humoral and cellular innate immune system by increasing lysozyme and complement activity, as well as neutrophil and monocyte populations. Our results suggest that ß-glucan-induced cortisol increase is one important mechanism to improve the innate immune response in matrinxã.

The immune system is limited by oxidative stress: Dietary selenium promotes optimal antioxidative status and greatest immune defense in pacu Piaractus mesopotamicus.

Reactive oxygen species (ROS) are reactive molecules containing oxygen, that form as byproducts of aerobic metabolism, including immune system processes. Too much ROS may cause oxidative stress. In this study, we examined whether it can also limit the production of immune system compounds. To assess the relationship between antioxidant status and immunity we evaluated the effect of dietary supplementation with organic selenium, given at various levels for 10 days, on the antioxidant and immune system of the pacu fish (Piaractus mesopotamicus). Fish fed a diet containing 0.6 mg Se-yeast kg(-1) showed significant improvement in antioxidant status, as well as in hematological and immunological profiles. Specifically, they had the highest counts for catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), red blood cells, and thrombocytes; the highest leukocyte count (particularly for monocytes); and the highest serum lysozyme activity. There was also a positive correlation between GPx and lysozyme in this group of fish. These findings indicate that short-term supplementation with 0.6 mg Se-yeast kg(-1) reestablished the antioxidative status, allowing the production of innate components which can boost immunity without the risk of oxidative stress. This study shows a relationship between oxidative stress and immunity, and, from a practical perspective, shows that improving immunity and health in pacu through the administration of selenium could improve their growth performance.

Energy deficit does not affect immune responses of experimentally infected pacu (Piaractus mesopotamicus).

We investigated if the energy deficit following a 30-day starvation period could affect the ability of fish to mount immune responses after experimental exposure to Aeromonas hydrophila. Fish were submitted to two feeding strategies during 30 days: starvation and continuously feeding. Fish were then sampled to allow for the assessment of baseline metabolic and immune system indicators, were next intraperitonially inoculated with A. hydrophila, and finally were sampled at 3 and 24 h after the challenge. The respiratory activity of leukocytes was lower in starved fish at baseline, increasing after bacterial inoculation to levels similar to those seen among fed fish. Levels of serum lysozyme were higher in starved fish at baseline. The same response profile was observed 3 h after inoculation, but among fed fish, these levels increased to values similar to those of starved fish 24 h after infection. Among starved fish, lysozyme concentration did not change over the course of the experiment. The serum ACH activity was lower in starved fish at baseline and increased after bacterial inoculation in both fish groups. Baseline levels of blood glucose of starved fish were lower than those of fed fish and increased 3 h after bacterial inoculation in both fish groups, decreasing in both groups at 24 h after inoculation. Baseline liver glycogen levels were similar in both fish groups and higher than at 3 and 24 h after inoculation. Three hours after bacterial inoculation, liver glycogen was less reduced in fed fish. Baseline levels of blood triglycerides were lower in starved fish and the profile remained unchanged 3 h after inoculation. There was a gradual decrease in fed fish, and the levels of starved fish remained unchanged throughout the observation period. Blood glycerol levels at baseline were higher in starved fish than in fed fish and remained unaltered at 3 h after inoculation. However those levels increased at 24 h. In fed fish there was a gradual increase of glycerol levels up to 24 h after bacterial inoculation. Baseline liver lipid levels of starved fish were lower and this difference in the response profile remained unchanged 3 and 24 h after inoculation. The liver lipid levels of starved fish decreased after inoculation, and remained unchanged in fed fish. As observed in liver lipid, muscle lipid levels of starved fish were lower than in fed fish, throughout the experiment. Starved fish levels remained unchanged; however fed fish levels decreased 24 h after bacterial inoculation. Levels of cortisol were higher in starved fish at baseline and increased in both fish groups 3 h after bacterial inoculation, reaching intermediary levels 24 h after inoculation. Our results show that in pacu, although mounting an immune response triggered after bacterial exposure is an energy-expensive process, fish under energetic deficit status were able to display protection against infection.

Aloe vera bathing improved physical and humoral protection in breeding stock after induced spawning in matrinxã (Brycon amazonicus).

In this study, we show that induced spawning causes stress, an intense loss of epithelia and immunosuppression, decreasing physical and humoral protection in fish, effects that were prevented or improved in fish bathed with Aloe vera. A. vera has several medicinal properties, including wound healing and immunostimulatory effects, which we observed in this study. Fish bathed with A. vera had a higher number of epidermal goblet cells and, in general, an improved wound healing rate compared with the control after induced spawning. These effects might be related to (1) the stimulation of leukocyte activity, represented here by the increased leukocyte respiratory activity triggered by A. vera (leukocytes are recognized as playing an important role in wound repair); (2) the antimicrobial properties of A. vera, which decrease wound infection and accelerate the healing process; and (3) several mechanisms that explain the healing effect of A. vera (increased collagen synthesis, rate of epithelialization, and anti-inflammatory and moisturizing effects). Our results also suggest that caution is necessary during the induced spawning process, especially during stripping, and A. vera bathing is recommended after intensive aquaculture operations.

Fish Immunology. The modification and manipulation of the innate immune system: Brazilian studies.

The understanding of fish immune system structure and function is essential for the development of new technologies and products to improve productivity. This is the first review on immune system of fish with Brazilian studies. Aquaculture in Brazil has shown massive growth in recent years due to methods of culture intensification. However, these procedures led to disease outbreaks, as well as the chemotherapy and the misuse of antibiotics. A viable alternative to avoid the use of chemicals and prevent economic losses is the administration of immunostimulants and prebiotcs, which act by increasing the innate immune system. In Brazil there is a lack of studies on fish immune system, except by some groups that have studied the effects of the immunostimulants administration in various species.

Effect of beta 1, 3 glucan in stress responses of the pencilfish (Nannostomus trifasciatus) during transport within the rio Negro basin

We investigated the use of beta 1,3 glucan as an imunostimulant during a transport experiment to determine the effects upon the stress response of the pencilfish (Nannostomus trifasciatus). Pencilfish were fed for seven days with different concentrations of beta 1,3 glucan: 0.0% (control); 0.01%; 0.1% and 0.5% of beta 1,3 glucan per kg of feed-1. Fish were then transported for 24 hours by boat from Barcelos to Manaus. The highest dose of beta 1,3 glucan in the food increased Na+ influx after 12 hours of transport and 0.1 and 0.5% beta 1,3 glucan maintained the flux of both ions close to zero at 24 hours. All doses of beta 1,3 glucan reduced K+ loss significantly in the beginning of the transport, but after 12 to 24 hours did not. No significant differences in whole body cortisol or survival were observed. Our results indicate that pencilfish had ionic alterations during transport from Barcelos to Manaus. The lack of significant differences in whole body cortisol and survival rate in addition to the maintenance of Na+ and K+ balance during transport reinforce the positive effects of beta 1,3 glucan immunostimulant on fish homeostasis. Therefore, we recommend its addition to food prior to transport...

O objetivo deste trabalho foi verificar se o imunoestimulante beta 1,3 glicano, adicionado à ração fornecida dias antes do transporte, pode minimizar algumas respostas de estresse do peixe lápis (Nannostomus trifasciatus) capturado na natureza. Estes peixes foram alimentados por sete dias com diferentes concentrações de beta 1,3 glicano: 0,0% (controle); 0,01 %; 0,1% e 0,5 % de beta 1,3 glicano.kg de ração-1. Após este período, as caçapas foram transportadas via barco de Barcelos para Manaus, com duração de 24 horas. Nos peixes alimentados com a maior concentração de beta 1,3 glicano na ração foi verificado aumento no influxo de Na+ após 12 horas de transporte e nos peixes alimentados com 0,1 e 0,5% de beta 1,3 glicano, o fluxo destes íons foi mantido próximo de zero no final de 24 horas de transporte. Todas as doses de beta 1,3 glicano reduziram significativamente a perda de K+ no início do transporte, mas, após 12 horas até o final do transporte houve efeito significativo no efluxo de K+. Não foram verificadas diferenças significativas entre tratamentos ou tempos de amostragem para os níveis de cortisol corpóreo. A taxa de sobrevivência não diferiu ao final do experimento. Nossos resultados indicam que o transporte entre Barcelos e Manaus promoveu alterações iônicas no peixe-lápis e a ausência de diferenças significativas no cortisol corpóreo e na taxa de sobrevivência aliada, à manutenção do equilíbrio de sódio e potássio durante o transporte, reforça o efeito positivo do imunoestimulante beta 1,3 glicano na homeostase dos peixes e sua adição à ração é recomendada...