Effects of diel variation of dissolved oxygen on blood physiological and biochemical indexes and hemoglobin genes response expression in Siniperca chuatsi

【Objective】This study aimed to investigate the response patterns of blood physiological and biochemical indexes and hemoglobin genes（Hb） expression of Siniperca chuatsi under the condition of diel variation of dissolved oxygen in aquaculture water, providing theoretical basis for further study on the short-term hypoxia adaptation mechanism in fish. 【Method】Healthy juvenile S. chuatsi were used as research objects. The Hb genes sequences were identified by matching the transcriptome sequencing and genome sequencing data, and bioinformatics analysis was carried out. Blood samples were collected at 4 consecutive time points: 7:00, 11:00, 17:00 and 23:00. Red blood cell（RBC） count, hemoglobin（HGB） concentration, hematocrit（HCT）, mean corpuscular hemoglobin concentration（MCHC） and mean corpuscular volume（MCV） were determined by using a PROCANPE-6800 blood cell analyzer. The expression levels of Hb genes were detected by real-time fluorescence quantitatively PCR（q RT-PCR）. 【Result】A total of 11 Hb genes were identified, including six α-Hb genes（hbae4, hbae, hbae1.1, hbae5, hbaa1 and hbaa1.1） and five β-Hb genes（hbbe2, hbba2.1, hbba1, hbba1.1 and hbba2）. Except the hbae4 gene sequence, which was composed of 6 exons and 5 introns, the other 10 gene sequences were all composed of 3 exons and 2 introns. The 11 S. chuatsi hemoglobin had no transmembrane structure or signal peptide and the subcell were located in the cytoplasm. Their secondary structures were composed of α-helix, β-turn, extended chain and random coil. A periodic diel variation of dissolved oxygen content was observed in the pond water. RBC count, HCT, HGB concentration and MCHC were the highest when the dissolved oxygen concentration was the lowest（7:00）, which were significantly higher than those at the other three time points（P＜0.05, the same below）. At the highest dissolved oxygen concentration（17:00）, RBC count, HCT, and HGB concentration significantly lower than those at the other three time points. There was no significant change in MCV among the four time points（P＞0.05）. The relative expression levels of hbae4, hbae, hbae1.1, hbae5, hbaa1.1, hbbe2, hbba2.1, hbba1 and hbba2genes showed an overall trend of first increasing and then decreasing with diel variation of dissolved oxygen, reaching the highest value at 17:00. The expression patterns of these nine Hb genes at the four time points were basically the same, that was, the relative expression level was the lowest at low dissolved oxygen concentration and the highest at high dissolved oxygen concentration. The relative expression of hbaa1 and hbba1.1 genes were inversely proportional to dissolved oxygen concentration. 【Conclusion】S. chuatsi adapts to diel variation of dissolved oxygen by regulating RBC count, HGB concentration, MCHC and Hb gene expression to maintain stable oxygen supply to the body.