Search

Simple Summary: This study aimed to identify the regions of the skin of a South American catfish with a higher number of mucous cells. Additionally, the effects of stressful conditions that may occur in fish cultures, such as different stocking densities and food deprivation, on the number of mucous cells in the skin and gills and their impact on cutaneous mucous lysozyme activity were investigated. The sampled catfish were exposed to the conditions of high stocking density (32 kg/m3) and fed, high stocking density and fasted, low stocking density (2.5 kg/m3) and fed, and low stocking density and fasted. After 14 days, samples of cutaneous mucous and skin fragments from seven different points and the second left branchial arch were collected. The ventral point in front of the ventral fin was the portion with the highest number of mucous cells. The number of mucous cells in both the skin and gills varied based on the collection point and treatment applied. The highest lysozyme activity in the epidermal mucous was observed in fish exposed to high stocking density and fed. Stocking density and food deprivation create stressful conditions for this type of catfish, which modulate its mucosal response in the skin to each situation. This study aimed to identify the regions of the body surface of silver catfish (Rhamdia quelen) with a higher population of mucous cells in the skin. Additionally, the effects of stressful conditions, such as different stocking densities and food deprivation, on the proliferative response of mucous cells in the skin and gill epithelium and their impact on cutaneous mucous lysozyme activity were investigated. Silver catfish were divided into four experimental groups: high stocking density (32 kg/m3) and fed (HSD-F), high stocking density and fasted (HSD-FS), low stocking density (2.5 kg/m3) and fed (LSD-F), and low stocking density and fasted (LSD-FS). Fish in the fed groups received commercial feed twice a day, amounting to 1% of the tank biomass. After a 14-day experimental period, the fish were anesthetized and euthanized. Samples of cutaneous mucous and skin fragments from seven different points and the second left branchial arch were collected. Histological slides of the skin and gills were stained with PAS + Alcian Blue at pH 2.5, and the epidermal mucous lysozyme activity was assessed using the turbidimetric method. The ventral point in front of the ventral fin was found to be the optimal location for collecting cutaneous epithelia due to its higher density of mucous cells. The population of mucous cells in both the skin and gills varied based on the collection point and treatment applied. The highest lysozyme activity in the epidermal mucous was observed in fish from the HSD-F group. Overall, these findings suggest that stocking density and food deprivation create stressful conditions for silver catfish, which modulate their mucosal response to each situation. [ABSTRACT FROM AUTHOR]

Abstract Citrobacter freundii is a fish pathogen known for its ability to cause injury and high mortality. There have been no studies reporting the effect of this bacterium on hematological parameters and internal organ histology in silver catfish (Rhamdia quelen). Therefore, the aim of this study is to evaluate the hematological and histopathological effects of an experimentally induced C. freundii infection in silver catfish. Twenty fish were divided into healthy and infected groups. The fish of the infected group were inoculated intramuscularly with 100 μL of bacterial suspension (6.4 × 108 CFU mL−1), while healthy control animals received 100 μL of sterile saline. On day 18 post-infection, blood and tissues (cephalic kidneys, livers, and spleens) were collected for histological analysis. The infected animals presented high mortality, as well as hematological and histological changes. In relation to hematology, the infected fish presented aregenerative anemia, protein loss, leukopenia with neutropenia, lymphocytosis, and leukoblastosis. Regarding histology, there was liver degeneration, decrease in the amount of renal hematopoietic tissue, and the presence of melanomacrophage centers (MMCs) in the spleen and cephalic kidney of infected fish. In summary, these alterations may contribute to disease pathophysiology, contributing to high mortality of affected fish. Highlights • Citrobacter freundii infection affects hematological parameters of silver catfish. • There was also liver degeneration, decrease in the renal hematopoietic tissue, and presence of MMCs in the spleen and kidney. • These alterations may contribute to disease pathophysiology, contributing to high mortality of affected fish. [ABSTRACT FROM AUTHOR]

Oxidative stress has been linked to a pathological mechanism that contributes to the initiation and progression of hepatic injury during Ichthyophthirius multifiliis infection. Thus, natural compounds with antioxidant and free radical scavenger properties, such as the Melaleuca alternifolia essential oil (TTO), might help to prevent or reduce hepatic damage. Thus, the aim of this study was to investigate whether TTO is capable of preventing or reducing hepatic oxidative damage in silver catfish naturally infected with I. multifiliis. After a TTO bath treatment of 1 h/day for 4 days, the number of trophonts on the skin of catfish was reduced by 94.87% compared to the control group. Hepatic samples from fish infected by I. multifiliis showed increased thiobarbituric acid reactive substances (TBARS) and protein carbonylation levels, while catalase (CAT) activity decreased compared to uninfected and untreated animals. Moreover, the histopathology analyses demonstrated the presence of necrosis, nuclear lateralization and cariorrexis, as well as swelling and vacuolization of cytoplasm. Treatment with TTO reduced hepatic TBARS and protein carbonylation levels and ameliorated the antioxidant system of infected fish, as well as preserve the hepatocytes morphology, but not prevented the occurrence of necrosis. Based on our findings, we propose that TTO is an alternative therapeutic option for silver catfish infected with I. multifiliis . Moreover, TTO treatment is a useful approach for avoiding or minimizing the hepatic oxidative stress caused by I. multifiliis, thus improving the hepatic antioxidant system. [ABSTRACT FROM AUTHOR]

Cytosolic and mitochondrial creatine kinases (CK), through the creatine kinase-phosphocreatine (CK/PCr) system, provide a temporal and spatial energy buffer to maintain cellular energy homeostasis. However, the effects of bacterial infections on the kidney remain poorly understood and are limited only to histopathological analyses. Thus, the aim of this study was to investigate the involvement of cytosolic and mitochondrial CK activities in renal energetic homeostasis in silver catfish experimentally infected with Aeromonas caviae. Cytosolic CK activity decreased in infected animals, while mitochondrial CK activity increased compared to uninfected animals. Moreover, the activity of the sodium-potassium pump (Na + , K + -ATPase) decreased in infected animals compared to uninfected animals. Based on this evidence, it can be concluded that the inhibition of cytosolic CK activity by A. caviae causes an impairment on renal energy homeostasis through the depletion of adenosine triphosphate (ATP) levels. This contributes to the inhibition of Na + , K + -ATPase activity, although the mitochondrial CK activity acted in an attempt to restore the cytosolic ATP levels through a feedback mechanism. In summary, A. caviae infection causes a severe energetic imbalance in infected silver catfish, which may contribute to disease pathogenesis. [ABSTRACT FROM AUTHOR]

Some studies have demonstrated that xanthine oxidase activity, through the regulation of uric acid levels, exerts a pro-inflammatory profile during infectious diseases. It has been recognized that uric acid induces the release of pro-inflammatory mediators, such as reactive oxygen species (ROS) and nitric oxide (NO), which contribute to inflammatory processes. Considering this, the aim of this study was to evaluate whether upregulation of branchial xanthine oxidase activity may be considered a pathway involved in ROS and nitric oxide (NOx) metabolites production in experimentally infected Rhamdia quelen (silver catfish) with Streptococcus agalactiae . Xanthine oxidase activity, and uric acid, ROS and NOx levels increased in gills of infected animals compared to uninfected animals. Moreover, a positive Pearson correlation was observed between uric acid and ROS levels, and between uric acid and NOx levels. Histopathology revealed the presence of necrosis, hyperplasia and vein congestion in gills of animals infected with S . agalactiae . Based on this evidence, the upregulation of xanthine oxidase activity induces a pro-inflammatory and oxidative profile in the gills of fish infected with S . agalactiae . The excessive uric acid levels induce the release of pro-inflammatory mediators, such as ROS and NOx, which contribute to disease pathogenesis. In summary, the upregulation of xanthine oxidase activity may be considered a pathway involved in ROS and NOx production. [ABSTRACT FROM AUTHOR]

Aeromonas hydrophila is one of the main causative agent of high mortality and significative economic losses in aquaculture and has become increasingly resistant to conventional antibiotics. One feasible alternative to control and treat it is the use of essential oils. This study aimed to evaluate A. hydrophila susceptibility to tea tree oil (TTO- Melaleuca alternifolia ) in vivo , and the effect of this treatment. In vivo tests were performed using silver catfish ( Rhamdia quelen ) as the experimental model. Silver catfish were treated with TTO at 25 and 50 μL/L for seven days before infection. After seven days, the fish were inoculated with A. hydrophila via intramuscularly. Treatment with TTO at 50 μL/L was able to extend longevity of infected fish, and showed 88% of therapeutic success, even though it did not show curative efficacy. TTO treatment was not toxic under these tested concentrations, since biomarkers of hepatic and renal functions were not affected, and the concentration of 50 μL/L was able to prevent increased levels of aspartate aminotransferase. There was no significative differences regarding hematological parameters (p < 0.05). Treatment with TTO 50 μL/L was able to reduce histopathological alterations usually caused by this type of bacteria in the gills, but it was unable to reduce hepatic histopathological alterations. Our results showed, for the first time, that TTO has high activity against A. hydrophila and proved to be a natural alternative to prevent and control this pathogen. [ABSTRACT FROM AUTHOR]

Flavobacterium columnare, the causative agent of columnaris disease, is a serious bacterial disease responsible for causing devastating mortality rates in several species of freshwater fish, leading to severe economic losses in the aquaculture industry. Notwithstanding the enormous impacts this disease can have, very little is known regarding the interaction between the host and bacterium in terms of the mortality rate of silver catfish (Rhamdia quelen), as well its linkage to gill energetic homeostasis. Therefore, we conducted independent experiments to evaluate the mortality rates caused by F. columnare in silver catfish, as well as whether columnaris disease impairs the enzymes of the phosphoryl transfer network in gills of silver catfish and the pathways involved in this inhibition. Experiment I revealed that clinical signs started to appear 72 h post-infection (hpi), manifesting as lethargy, skin necrosis, fin erosion and gill discoloration. Silver catfish began to die at 96 hpi, and 100% mortality was observed at 120 hpi. Experiment II revealed that creatine kinase (CK, cytosolic and mitochondrial) and pyruvate kinase (PK) activities were inhibited in silver catfish experimentally infected with F. columnare , while no significant difference was observed between experimental and control groups with respect to adenylate kinase activity. Activity of the branchial sodium-potassium pump (Na+, K+-ATPase) was inhibited while reactive oxygen species (ROS) and lipid peroxidation levels were higher in silver catfish experimentally infected with F. columnare than in the control group at 72 hpi. Based on these data, the impairment of CK activity elicited by F. columnare caused a disruption in branchial energetic balance, possibly reducing ATP availability in the gills and provoking impairment of Na+, K +ATPase activity. The inhibition of CK and PK activities appears to be mediated by ROS overproduction and lipid peroxidation, both of which contribute to disease pathogenesis associated with branchial tissue. • Branchial CK activity is inhibited in silver catfish infected with F. columnare. • Branchial PK activity is inhibited in silver catfish infected with F. columnare. • ROS levels were higher in silver catfish infected with F. columnare. • Impairment on phosphotransfer network contribute to pathogenesis of columnaris disease. [ABSTRACT FROM AUTHOR]