The effect of adding thymol to water on thyroid hormones, proteins and plasma enzymes in common carp (Cyprinus carpio)

Fish transportation in the aquaculture industry is one of the causes of stress and is inevitable. For this reason, providing methods to reduce transportation stress can improve fish health. The aim of this study was to investigate the effect of adding thymol to water on biochemical parameters of common carp during transportation. For this purpose, common carp were transported in plastic bags containing 0 (control), 5 and 10 mg/L thymol (three plastic bags per concentration) for 3 hours. Plastic bags were filled with 4 liters water and 8 liters pure oxygen. Blood samples were taken from all treatments immediately after transportation and 24 hours after recovery. The results showed that fish transportation and thymol concentration had no effect on the activity of alanine aminotransferase, alkaline phosphatase, total protein, globulin, albumin, and thyroxin in the fish blood plasma. On the other hand, after transportation, blood aspartate aminotransferase and lactate dehydrogenase activity increased and blood triiodothyronine levels decreased. Thymol, especially at a concentration of 5 mg/L, reduced the effect of transport on the activity of aspartate aminotransferase, lactate dehydrogenase and blood triiodothyronine. These results show that thymol reduces the stress and metabolism of carp during transportation. Therefore, a concentration of 5 mg/L thymol is recommended for short-term transportation of common carp.