Abstract:There are approximately 64 million hm2 of low-lying saline-alkali water resources in inland China, accounting for 55% of the total lake area. The characteristics of saline-alkali water are: high salt content, high alkalinity (high pH), and complex ion composition. Most freshwater fish cannot survive or reproduce in these conditions. To utilize saline-alkali water resources for aquaculture, researchers have introduced salt-tolerant fish, such as Luciobarbus capito, Chalcalburnus chalcoides aralensis, Leuciscus waleckii, and Oreochromis niloticus. In the initial stage of aquaculture, fish fry are not yet adapted to saline-alkali conditions because their body structure and physiological functions are not underdeveloped. The survival rate of juvenile fish is low because of the stress response to saline-alkali water. Studies of saline-alkali aquaculture have shown that proper acclimation can effectively improve the survival rate, growth, antioxidant, and immune properties of fish. L. capito belongs to the Cyprinidae family (subfamily Barbinae). It occurs mainly in the Caspian Sea and the Aral Sea of Western Asia. L. capito is an economically important fish, with adults weighing 5~ 10 kg. The species has excellent breeding characteristics, high saline-alkali tolerance, varied food habits, fast growth, delicious meat, and strong stress resistance. In 2003, it was introduced from Uzbekistan to China. To date, research has reported on L. capito artificial breeding technology and breeding biology but has not yet considered salt-alkali domestication. To study the physiological adaptability of L. capito to alkalinity with regards to blood physiology, biochemistry, and antioxidative stress, we used juvenile L. capito (13.66±1.26) g to test NaHCO3 alkalinity acclimation. The control group was cultivated in freshwater. The acclimation group was subjected to 20 mmol/L alkalinity for 7 d and then placed in 40 mmol/L alkaline water. The non-acclimation group was placed in 40 mmol/L alkaline water. The experimental media were prepared with tap water and NaHCO3 (domestic, analytically pure) after aeration for 2 d, and the alkalinity was measured and calibrated by acid-base titration. The fish were fed once a day and fasted for 24 h before sampling. Blood physiological and biochemical indices (water osmotic pressure, white blood cells, lymphocytes, neutrophils, monocytes, hemoglobin, red blood cells, platelets, platelet hematocrit, urea, and albumin), as well as indices related to the liver antioxidant system of juvenile fish in 40 mmol/L alkalinity water, were measured at 0 h, 6 h, 12 h, 24 h, 48 h, 96 h, and 7 d. In the control group, the same sampling was conducted at the corresponding moments. The physiological and biochemical indices for both domesticated and non-domesticated fish initially increased and then decreased across the sampling period (P<0.05). In both the domesticated and non-domesticated groups, the antioxidant indices of fish liver tissue, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA), increased initially and then decreased across the sampling period (P<0.05). The peak values of each parameter in the domesticated group were significantly lower than those of the non-domesticated group (P<0.05). No significant changes were observed in the control group during this period (P>0.05). The peak values of leukocytes, lymphocytes, neutrophils, and monocytes appeared at 48 h in the acclimated group and at 24 h in the non-acclimated group; the blood hemoglobin content, red blood cell content, platelet content, hematocrit, SOD, and CAT peaked in both the acclimated and non-acclimated groups at 24 h. After 7 d, the urea, lymphocyte, monocyte, platelet, red blood cell, hemoglobin, and albumin content of the blood and aspartate aminotransferase (AST), alanine aminotransferase (ALT), SOD, CAT, GSH-PX, and MDA content of the liver tissue were significantly lower in the acclimation group than in the non-acclimation group (P<0.05), but the plasma albumin content and glutathione catalase in the acclimated group returned to the level of the control group (P>0.05). Studies have shown that after alkalinity acclimation, juvenile L. capito are less stressed and the body tissue shows less damage and greater recovery under high alkalinity. At the physiological level, the body has higher adaptability. This study provides a theoretical basis for the establishment of saline-alkali aquaculture technology for the cultivation of L. capito that is based on the adaptability of the species to gradual changes in the alkalinity of the environment.
