Methanolic extract of Condalia buxifolia added to transport water alters biochemical parameters of the silver catfish Rhamdia quelen

The effects of the methanolic extract of Condalia buxifolia (MECB) were investigated in silver catfish (Rhamdia quelen) transported for 6h in plastic bags at 0, 5 or 10μL/L MECB. Prior to transport, the fish were sedated with 10μL/L MECB for 5min, except the control group. At the end of transport, dissolved oxygen, alkalinity, pH, temperature, and un-ionized ammonia levels in the transport water were not different between groups, but the control group presented the highest total ammonia levels. Net Na+, Cl− and K+ effluxes were highest in fish from the control group compared to those transported with MECB. PvO2, PvCO2 and HCO3− were higher after transport in fish transported with 5μL/L MECB, but no significant difference between groups was found regarding blood pH and plasma cortisol levels. The metabolic parameters (glycogen, lactate, total amino acid, total ammonia and total protein) were lower or no significant difference was found in fish transported with MECB. There was no difference between treatments on the ecto-nucleoside triphosphate diphosphohydrolase, 5′-nucleotidase and acetylcholinesterase activities in the whole brain. The activity of all analyzed antioxidants increased in the gills and superoxide dismutase and glutathione-S-transferase also increased in the other analyzed tissues. In addition, lipoperoxidation (measured by thiobarbituric acid-reactive substances) and carbonylation of proteins (measured by protein carbonyl) decreased in most analyzed tissues, indicating lower ROS production. In conclusion, the use of MECB for the transport of silver catfish is advisable because MECB improves antioxidant defenses in several tissues and was effective in reducing waterborne total ammonia levels and ion loss. •Silver catfish were transported with methanolic extract of Condalia buxifolia (MECB) for six hours.•Fish transported with MECB did not have alterations in AChE, NTPDase and SOD activity.•MECB in the transport water is recommended for silver catfish because it improved the antioxidant capacity in some tissues.•MECB in the transport water was also effective in reducing waterborne total ammonia levels and ion loss.