Modulation of humoral immunological and antioxidant responses and gut bacterial community and gene expression in rainbow trout, Oncorhynchus mykiss, by dietary lactic acid supplementation.

The present study was conducted to find the effects of dietary lactic acid (LA) supplementation on growth performance, hematological characteristics, humoral antioxidant and immunological factors, intestinal gene expression and bacteriological parameters in rainbow trout, Oncorhynchus mykiss. The fish (104 ± 0.90 g) were randomly distributed in twelve tanks (150 L water) as four treatments, receiving diets supplemented with 0, 5, 10, and 20 g/kg LA for 70 days. At the end of the feeding trial, no significant differences were observed in the fish growth performance and survival among the treatments. Blood/plasma red blood cell (5-20 g/kg LA), white blood cell (10 g/kg LA), hematocrit (5 and 10 g/kg LA), hemoglobin (5 and 10 g/kg LA), superoxide dismutase (10 g/kg LA), glutathione peroxidase (10 g/kg LA), total antioxidant capacity (10 g/kg LA), lysozyme (5-20 g/kg LA), and alternative complement activity (10 g/kg LA) significantly increased, as malondialdehyde (10 g/kg LA) significantly decreased in the LA-treated fish. Dietary LA supplementation induced no significant changes in the intestinal defensin gene expression, but significantly up-regulated the expression of toll-like receptor-3 (5-20 g/kg LA), Mx-9 (5-20 g/kg LA), and heat shock protein-70 (5 g/kg LA) genes; the highest expressions were observed at 5 g/kg LA supplementation. Dietary LA supplementation significantly increased total bacterial count (5 and 10 g/kg LA), Lactobacillus sp. (5-20 g/kg LA), and Bacteroides sp. (5-20 g/kg LA), but decreased Streptococcus iniae (5-20 g/kg LA) in the fish intestine; the highest Lactobacillus sp. And Bacteroides sp. Were observed in 10 and 5 g/kg LA supplementation, respectively. Overall, dietary LA supplementation, although has no significant effects on the fish growth performance, is beneficial to improve humoral antioxidant parameters, humoral and intestinal immunological parameters and intestinal microflora. According to the results, dietary 5-10 g/kg LA is recommended for the formulation of rainbow trout feed.

Histopathological damage and stress- and immune-related genes' expression in the intestine of common carp, Cyprinus carpio exposed to copper and polyvinyl chloride microparticle.

The present study aimed at assessing the singular and combined effects of water copper and polyvinyl chloride microplastic (MPVC) on intestinal copper accumulation, histopathological damage, and stress-/immune-related genes' expression in common carp, Cyprinus carpio. Four groups of fish were maintained in triplicate: control (kept in clean water), Cu (exposed to 0.25 mg/L of copper), MPVC (exposed to 0.5 mg/L of MPVC), and Cu-MPVC (exposed to 0.25 mg/L of copper + 0.5 mg/L of MPVC). After 14-day exposure, the fish of Cu and Cu-MPVC treatments exhibited significantly higher intestinal copper contents, compared to the fish of control and MPVC treatments. In this regard, the Cu-MPVC fish had significantly higher copper content than the Cu fish. Exposure to copper and/or MPVC significantly upregulated the intestinal heat shock protein 70 (hsp70), cytochrome P450 family 1 subfamily A member 1 (cyp1a1), lysozyme (lys), defensin (def), mucin 2 (muc2), and mucin 5 (muc5) expression. The highest expression of hsp70, cyp1a1, lys, and def was related to Cu-MPVC treatment; whereas, the highest expression of muc2 and muc5 was observed in Cu and MPVC treatments. Exposure to copper and/or MPVC induced intestinal damage, which Cu-MPVC fish exhibited the highest severity. The present study revealed that exposure to copper and/or MPVC causes intestinal histopathological damage and upregulation in stress- and immune-related genes' expression. The most serious effects were observed in Cu-MPVC treatment that might be due to additive effects of copper and MPVC and/or higher copper accumulation in this treatment.