Effect of sub-chronic exposure to selenium and Allium mongolicum Regel flavonoids on Channa argus: Bioaccumulation, oxidative stress, immune responses and immune-related signaling molecules.

Selenium (Se) is a micronutrient that becomes toxic when present at higher concentrations in fish tissues. Allium mongolicum Regel flavonoids (AMRF) have been documented to possess antioxidant, immunoenhancement and anti-inflammation properties. The aim of this study was to investigate the protective effects and potential mechanisms of dietary supplementation of AMRF and Se exposure on oxidative stress, immune responses and immune-related genes expression in Channa argus. A total of 480 C. argus were randomly divided into eight groups housed in twenty-four 200 L glass aquarium (3 tanks per group, 20 fish per tank). The fish were exposed for 56 days to waterborne Se at 0, 50, 100 and 200 µg/L and/or dietary AMRF at 40 mg/kg. The result indicated that AMRF exerted significant protective effects by preventing alterations in the levels of bioaccumulation, malondialdehyde, lysozyme, complement C3 and immunoglobulin M. AMRF also assists in the elevation of catalase and glutathione peroxidase in the liver and spleen while regulating the expression of immune-related genes including NF-κB p65, IκB-α, TNF-α, IL-1ß, IL-8, HSP70, HSP90, and glucocorticoid receptor after 56 days of Se exposure. Our results suggest that administration of AMRF (40 mg/kg) has the potential to combat Se toxicity in C. argus.

Modulatory role of L-carnitine against microcystin-LR-induced immunotoxicity and oxidative stress in common carp.

Microcystin-LR (MCLR), one of the most popular microcystins (MCs) found in many field water bodies around the world, poses great health risks to animals and humans. In the present study, healthy common carp (initial weight 24.8 ± 2.3 g) were randomly assigned to five groups. Group I was fed on normal diet as control. Group II was maintained on normal diet and received MCLR intraperitoneal injection (150 µg kg-1 BW). Common carp in groups III, IV, and V were daily pretreated with L-carnitine (LC) at doses of 0.5, 1.0, and 2.0 g kg-1 of the diet for 4 weeks prior to MCLR intraperitoneal injection. The results showed that MCLR alone led to a significant downregulation in immune response, including serum complement C3, lysozyme, and bactericidal activity. However, oxidative stress response: catalase (CAT), superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GPx), and lipid peroxidation (LPO) levels were significantly increased. Similarly, gene expressions of inflammatory IL-1ß, TNF-α, IFN I, and heat shock proteins (HSP70 and HSP90) were also upregulated after challenged with MCLR. However, LC pretreated group caused a significant elevation in immune response (C3, lysozyme, and bactericidal activity) and gene expressions of inflammatory IL-1ß, TNF-α, IFN I, and heat shock proteins (HSP70 and HSP90) after MCLR stress. Antioxidant activities (CAT, SOD, GSH, GPx, and LPO) were returned to background levels at 96 h after MCLR challenge. Strikingly, LC supplementation at 2.0 g kg-1 has been considered the optimum for common carp since it exhibited enhancement of immune response and antioxidant activity over the level 0.5 and 1.0 g kg-1, and even better than that of control level. It was concluded that LC as a functional feed additive significantly inhibited the progression of MCLR-induced immunotoxicity and oxidative stress in common carp.

Effects of Ala-Gln feeding strategies on growth, metabolism, and crowding stress resistance of juvenile Cyprinus carpio var. Jian.

The present study was conducted to evaluate the effects of different L-alanyl-l-glutamine (Ala-Gln) feeding strategies on the growth performance, metabolism and crowding stress resistance related parameters in juvenile Jian carp (Cyprinus carpio var. Jian) under crowded condition (80 g/L). Juvenile Jian carp (initial weight 26.1 ± 0.6 g) were distributed into five groups which fed with graded concentrations (0% or 1.0%) of Ala-Gln for eight weeks. Control group (I, 0/0) fed with control diet (0% Ala-Gln) throughout the feeding trial. The other four groups employed different control and experimental diet feeding strategies ranging from two weeks control diet fed and two weeks experimental diet (1% Ala-Gln) fed (II, 0/2) to eight weeks experimental diet fed (V, 4/4). Results revealed that Mean weight gain (MEG) under all different feeding strategies of Ala-Gln were significantly higher than that of the control group (p < 0.05), and MEG of group II (201.90%) was even higher than that of group IV (184.70%). Liver glycogen and blood total protein of groups II, III and V were significantly higher than that in groups I and IV (p < 0.05). The highest level of serum thyroxine (10.07 ng/ml), insulin-like growth factor-I (52.40 ng/ml) and insulin (9.73 µ IU/mL) were observed in group V. However, diet supplemented with Ala-Gln did not affect the levels of serum glucose, cortisol and catecholamine in fish. The mRNA expression of GR1a, GR1b and GR2 were also significantly changed in Ala-Gln supplementation groups compared with control group (p < 0.05). After fish intraperitoneally injected with virulent Aeromonas hydrophila, the fish survival rates were significantly increased in all Ala-Gln supplementation groups compared with control group (p < 0.05). Results from the present experiment showed the importance of dietary supplementation of Ala-Gln in benefaction of the growth performance, metabolism and crowding stress resistance in Jian carp breeding. The optimal feeding strategy was alternatively fed with control diet and then experimental diet at an interval of two weeks for juvenile Jian carp under crowded condition.