Abstract
ABSTRACT This study aimed to assess the effects of low and high water hardness in interaction with different water pH in pacu (Piaractus mesopotamicus). Pacu juveniles were subjected to low (50 mg CaCO3 L-1 - LWH) or high water hardness (120 mg CaCO3 L-1 - HWH) at water pH of 5.5 (acidic), 7.5 (circumneutral) or 9.0 (alkaline) for 15 days. Gills and kidneys were collected (days 1, 5 and 15). Gill Na+/K+-ATPase (NKA) and vacuolar-type H+-ATPase (V-ATPase) activities were higher in alkaline pH with HWH on day 1. Gill and kidney NKA and V-ATPase activities were higher in acidic pH with LWH on day 15. Gill NKA activity of pacus under alkaline pH with LWH was higher than those exposed to HWH. Reduced antioxidant capacity in the gills and kidney and enhanced thiobarbituric acid reactive substances (TBARS) levels were demonstrated in fish exposed to acidic or alkaline pH, mainly with LWH. HWH increased glutathione-S-transferase (GST) activity and reduced TBARS levels in the gills and kidney. On day 15, GST activity was increased at acidic pH with LWH. In conclusion, circumneutral pH presents less oxidative stress and fewer variations in ATPases and HWH reduced deleterious effects in fish exposed to acidic or alkaline pH.
Highlights
The relationship between water pH and hardness influences fish development and welfare (Baldisserotto, 2011; Copatti et al, 2011a,b)
Na+/K+-ATPase (NKA) and vacuolar-type H+-ATPase (V-ATPAse) activities in the gills and kidney of pacu (Piaractus mesopotamicus) juveniles submitted to different pH and water hardness at different times
Copatti et al (2011a) stated the protective effect of high water hardness (HWH) occurs because the high ion loss is reduced by increasing the water hardness in acidic or alkaline pH, which could cause an improvement in the osmoregulation and antioxidant capacity of the fish in these water pH values
Summary
The relationship between water pH and hardness influences fish development and welfare (Baldisserotto, 2011; Copatti et al, 2011a,b). Freshwater fish survival is greater at very acidic or alkaline water pH when fish are in high rather than in low water hardness (Baldisserotto, 2011). Calcium is important at stabilizing tight junctions in the gills and reduces their permeability, contributing to osmoregulatory homeostasis and survival of fish by limiting diffusive branchial ion loss to the water by paracellular route (Baldisserotto, 2011; Chasiotis et al, 2012). One of the survival mechanisms of species living in waters of very low hardness is a high affinity for calcium, which would contribute to closing paracellular junctions in the gills (Gonzalez et al, 1998)
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