Common salt (99.3% of sodium chloride) is used as a water additive to reduce management stress in ornamental fish. Therefore, specific information on fish tolerance to water salinity is needed for establishing safe limits for salt use. In this study, we aimed to evaluate juvenile platy, Xiphophorus maculatus, for stress response and tolerance to acute salinity exposure. The fish were exposed to 0, 5, 10, 15, 20 and 25 g common salt/L water, for 96 h. Each aquarium containing 15 fish was considered an experimental unit. Mortality was quantified throughout the all‐experimental period, and blood glucose was measured at 24 and 96 h. Survival probability was high (>90%) in platy exposed to 0, 5 and 10 g common salt/L water. The median lethal concentration (LC50) was estimated at 16.54 g common salt/L water, by logistic regression analysis. Platy showed an increase in blood glucose at 24 h with increased salinity, but glucose levels decreased at 96 h of in fish exposed to 10 and 15 g/L. These findings suggest that short periods of exposure to common salt in water trigger stress responses in juvenile platy. Therefore, common salt should not be used in the handling and transport of platy, at the exposure times evaluated.
The dietary impacts of water-soluble (vitamin C) and fat-soluble (oregano essential oil, OEO) antioxidants on the stress responses and redox status of Astyanax aff. bimaculatus exposed to the air were assessed. Five diets with vitamin C (VC 0, VC 40, VC 80, VC 120, and VC 160 mg kg − 1 ) with or without OEO inclusion (0 or 1,000 mg kg − 1 ) were evaluated. After 55 days of feeding, sh were exposed to air for 5 min. VC 120 and VC 160 reduced glycemia. In the gills, VC 120 and VC 160 reduced oxidative damage (malondialdehyde, MDA, and carbonylated proteins, PC) and superoxide dismutase (SOD) activity only in the presence of OEO. By contrast, in the absence of VC, OEO increased PC levels and SOD activity. In the liver, all VC concentrations, without OEO, reduced MDA, whereas, in the presence of OEO, vitamin C reduced MDA only at VC 40 e VC 160. All vitamin C concentrations, independently of OEO, reduced PC levels and SOD and catalase (CAT) activity. By contrast, OEO increased CAT and glutathione S-transferase (GST) activity regardless of VC level. Although VC 40 with 1,000 mg kg − 1 OEO was su cient to reduce oxidative damage to lipids in the gills and liver, reduction in protein and lipid damage in the gills was only obtained with at least VC 120 + OEO. Therefore, we recommend simultaneous supplementation of these antioxidants, as their combined use is more e cient in reducing oxidative damage in A. aff. bimaculatus subjected to air.
The dietary impacts of water-soluble (vitamin C) and fat-soluble (oregano essential oil, OEO) antioxidants on the stress responses and redox status of Astyanax aff. bimaculatus exposed to the air were assessed. Five diets with vitamin C (VC 0, VC 40, VC 80, VC 120, and VC 160 mg kg− 1) with or without OEO inclusion (0 or 1,000 mg kg− 1) were evaluated. After 55 days of feeding, fish were exposed to air for 5 min. VC 120 and VC 160 reduced glycemia. In the gills, VC 120 and VC 160 reduced oxidative damage (malondialdehyde, MDA, and carbonylated proteins, PC) and superoxide dismutase (SOD) activity only in the presence of OEO. By contrast, in the absence of VC, OEO increased PC levels and SOD activity. In the liver, all VC concentrations, without OEO, reduced MDA, whereas, in the presence of OEO, vitamin C reduced MDA only at VC 40 e VC 160. All vitamin C concentrations, independently of OEO, reduced PC levels and SOD and catalase (CAT) activity. By contrast, OEO increased CAT and glutathione S-transferase (GST) activity regardless of VC level. Although VC 40 with 1,000 mg kg− 1 OEO was sufficient to reduce oxidative damage to lipids in the gills and liver, reduction in protein and lipid damage in the gills was only obtained with at least VC 120 + OEO. Therefore, we recommend simultaneous supplementation of these antioxidants, as their combined use is more efficient in reducing oxidative damage in A. aff. bimaculatus subjected to air.
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