Histopathological Studies of Experimentally Infected Shing, Heteropneustes fossiliswith Aeromonas hydrophila Bacteria

Potentials of Aloe barbadensis inclusion in fish feeds on resilience to Aeromonas hydrophila infection in freshwater fish Labeo rohita

Aquatic bacterial pathogens can cause severe economic loss in aquaculture industry. An opportunistic pathogen, Aeromonas hydrophila is responsible for Motile Aeromonas Septicemia, leading to high mortality rates in fish. The present study was focused on the efficacy of Aloe barbadensis replacing fishmeal diets on hematological, serum biochemical, antioxidant, histopathological parameters, and disease resistance against A. hydrophila infection in Labeo rohita. Isonitrogenous fishmeal replaced diets (FMR) were prepared with varying levels of A. barbadensis at D1 (0%) (control), D2 (25%), D3 (50%), D4 (75%) and D5 (100%) then fed to L. rohita. After 60 days of post-feeding, the experimental fish were challenged with A. hydrophila. Blood and organs were collected and examined at 1- and 15-days post infection (dpi). The results demonstrated that on 1 dpi, white blood cells (WBC), total protein, cholesterol and low-density lipoprotein (LDL) levels were significantly increased in D3 diet fed groups. The D2 and D3 diet fed group showed decreasing trends of serum glutamic pyruvic transaminase (SGPT) and antioxidant enzymes activity on 15 dpi. The histopathological architecture results clearly illustrated that the D3 diet fed group had given a higher protective effect by reducing the pathological changes associated with A. hydrophila infection in liver, intestine and muscle. Higher percentage of survival rate was also observed in D3 diet fed group. Therefore, the present study suggested that the dietary administration of A. barbadensis up to 50% fishmeal replacement (D3 diet) can elicit earlier antioxidant activity, innate immune response and improve survival rate in L. rohita against A. hydrophila infection.

Silymarin enhances the response to oxytetracycline treatment in Oreochromis niloticus experimentally infected with Aeromonas hydrophila

Many governments have approved the use of oxytetracycline as an antibiotic additive to food fish, with oxytetracycline now routinely used in many nations. However, oxytetracycline is known to have immunosuppression impacts. We, therefore, evaluated the immunological, antioxidative, and histopathological status of Nile tilapia fed a diet containing silymarin (100 mg/kg fish feed) for 0, 2, 4, 6, and 8 weeks. The protective effects of silymarin against Aeromonas hydrophila (A. hydrophila) infection and oxytetracycline treatment were evaluated. Blood parameters (erythrocyte count, white blood cell count, hemoglobin, and packed cell volume) improved over time in fish fed on dietary silymarin. Serum levels of alanine aminotransferase (ALT) were lower in fish fed on dietary silymarin, whereas serum levels of aspartate transferase (AST)and alkaline phosphatase (ALK) were unchanged. Dietary silymarin affected serum lipid profiles as decreases in serum triglyceride and low-density lipoprotein cholesterol levels and a trend toward lower cholesterol levels, whereas serum high-density lipoprotein cholesterol levels were increased compared to fish fed on the control diet. Dietary silymarin resulted in an increase of serum total protein levels and globulin fractions. Significant and progressive increases in catalase and glutathione peroxidase levels were observed after six weeks of feeding on a dietary silymarin before decreasing to control levels at the end of the experimental period. Fish fed on dietary silymarin, interleukin-1 and fish tumor necrosis factor-alpha were upregulated in hepatic tissues; however, interleukin-10 levels decreased to comparable levels to controls after eight weeks. Fish infected with A. hydrophila displayed septicemia (opaque eye, hemorrhagic ulcers, dentated fins, hepatomegaly, and splenomegaly). Reduced mortality was observed in Nile tilapia infected with A. hydrophila and fed a diet containing silymarin, indicating that silymarin improves fish responses to oxytetracycline with a 37% reduction in mortality.

Aquatic bacterial contamination associated with sugarplant sewage outfalls as a microbial hazard for fish

The aim of the study was to compare bacterial composition and load in waters and fish related to the wastewater treatment plant (WWTP), particularly waters and wild fish affected by sugarplant processing (sugar cane and sugar beet). Aeromonads were the most frequently isolated group from water and fish. A. hydrophila was a prevailing species in isolates from water, followed by A. veronii, Rheinheimera soli and Ochrobactrum anthropi. Of indicator bacteria for aquatic contamination from fish tissues, the most prominent were V. cholerae, Enterobacter cloacae and E. sakazakii. Sugar cane processing contributed to high viable cell counts at 37 °C while sugar beet processing contributed to high bacterial counts at 22 °C. Heterotrophs from gills of effluent fish were highest during sugar cane processing. Counts retrieved from fish skin were more uniform between effluent fish and fish from downstream waters. Antimicrobial resistance of bacteria isolated from water was high against amoxicillin, sulfamethoxazole, flumequine, norfloxacin and oxolinic acid in samples from the inflow of raw municipal wastewaters to WWTP, while resistance found in bacteria from the inflow of sugarplant mostly related to sulfamethoxazole and amoxicillin. The PCA analysis associated the occurrence of high heterotroph counts, P. aeruginosa, and intestinal enterococci on skin and gills with sugar cane, and yeasts and molds with sugar beet processing. Fish living in treated wastewaters and related water bodies could pose a microbial hazard if fished for human consumption, possibly causing infection when being handled and processed, as a risk of human pathogens penetrating fish tissues.

Effect of phytase enzyme on growth performance, serum biochemical alteration, immune response and gene expression in Nile tilapia

The present study aimed to investigate the effect of low phosphorus diet with or without different levels of phytase enzyme supplementation on growth performance, body composition, nutrient retention efficiency, gene expression, and health status of A. hydrophila challenged fish. A total of 240 monosex males of Nile tilapia (Oreochromis niloticus) with an average body weight of 23.19 ± 0.15 g/fish were used. Fish were randomly chosen and divided into 4 equal groups (60 fish per group), with 3 subgroups containing 20 fish as a replicate. Group 1, was fed on a diet containing 100% P, group 2, was fed on a diet containing 50% P, group 3 and 4, were fed on low P with 500 or 1000 units of phytase/Kg respectively. It was observed that the 50% phosphorus diet significantly reduced body weight, feed intake, feed conversion ratio (FCR), and protein efficiency ratio (PER) compared to Nile tilapia fish fed on the diet containing 100% phosphorus. In contrast, fish fed on the diet containing 50% phosphorus supplemented by 500 or 1000 phytase units/kg significantly (P ≤ 0.05) increased final body weight (FBW), total body gain (TBG), average daily gain (ADG), and weight gain compared to Nile tilapia fed on the same diet or fed on the diet containing normal phosphorus without phytase supplementation. Different phosphorus and phytase supplementation levels had no significant effect on serum total protein, albumin, and globulin concentrations, meanwhile, phytase supplementation increased serum calcium and phosphorus levels. Nile tilapia fed on phytase supplementation had an increase in body protein, lipid content, and nutrient utilization efficiency compared to Nile tilapia fed on the diet containing 100% phosphorus. Nile tilapia fed on low dietary phosphorus showed an increase in mortality after infection and a decrease in phagocytosis and neutrophil compared to fish fed on normal phosphorus. Phytase supplementation, made immune response parameters return to its normal values and the pathological lesions of liver, spleen, stomach, and intestine were reduced. Moreover, normal phosphorus significantly up-regulated lipoprotein lipase (LPL) mRNA expression and down-regulated fatty acid synthase (FAS) mRNA in Nile tilapia's liver while low phosphorus with or without phytase supplementation reduced LPL expression and relatively up-regulated FAS.

Characterization of Histopathological and Ultrastructural Changes in Channel Catfish Experimentally Infected with Virulent Aeromonas hydrophila

A highly virulent clonal population of Aeromonas hydrophila (vAh) has been the cause of recent motile Aeromonas septicemia epizootic in channel catfish (Ictalurus punctatus) farms in the Southeastern United States. The pathology of the disease caused by vAh has not been studied well yet. Thus, our aim was to determine histopathological and ultrastructural changes in channel catfish following vAh challenge. To accomplish this, catfish fingerlings were challenged with vAh (strain ML09-119) by bath. Six fish per each time point were collected at 1, 3, 5, 6, 24, and 48 h for light microscopy, and six fish were collected at 48 h for transmission electron microscopy (TEM). The first pathological lesions were detected in the spleen and stomach at 1 h post-challenge (HPC) while intestine, gills, kidney, and liver lesions were observed at 24 and 48 HPC. Histopathological examination revealed degenerative changes, necrosis, extensive edema, and inflammation in internal organs. The TEM showed severe tissue destruction with multiple bacterial cells secreting outer membrane vesicles, especially in spleen and gills and far number in the stomach. Degenerated bacterial cells were observed in the intestinal lumen and the phagosomes of phagocytic kidney cells. We identified, for the first time, degranulate eosinophilic granular cells, and dendritic cells like (DC-like) cells in the necrotic intestinal epithelium. These findings suggest that vAh rapidly proliferated and spread through the catfish organs following bath challenge.