Hypoxia tolerance, hematological, and biochemical response in juvenile turbot (Scophthalmus maximus. L)

Abstract

Hypoxia is a critical issue in aquaculture which affects the metabolism and survival of fish. The critical oxygen tension (Pcrit), loss of equilibrium (LOE), respiration frequency (RF), plasma cortisol, glucose, lactate, cholesterol (CHO), triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), total protein, albumin, globulin, albumin/globulin, white blood cell (WBC), red blood cell (RBC), hemoglobin (Hb) and hematocrit (Hct) of turbot (male vs female) were determined during hypoxia and reoxygenation to evaluate their hypoxia tolerance and underlying physiological response. Results showed that dissolved oxygen (DO) values at Pcrit and LOE were 3.34 ± 0.17 mg/L and 1.30 ± 0.16 mg/L, respectively. RF significantly increased at Pcrit and LOE. Meanwhile, abnormal swimming behaviors were observed at DO values lower than 5 mg/L. Male and female showed no significant difference in above indexes. Hypoxia stress significantly increased plasma cortisol, glucose, and lactate contents at Pcrit and LOE, with the highest value obtained at LOE. Female plasma cortisol and glucose content were significantly higher than males at LOE, whereas the male lactate was significantly higher than females. Hypoxia stress did not affect the WBC number, plasma CHO, HDL, LDL levels and albumin/globulin of the male and female turbot. Plasma TG and total protein, albumin, globulin levels significantly increased at LOE and Pcrit, respectively. Female total protein significantly higher than males at Pcrit, but the opposite trend was found at LOE. RBC, Hb and Hct manifested similar cortisol results, the male and female showed no significant difference. The aforementioned parameters except for cortisol were recovered to normal levels after reoxygenation for 12 h. In conclusion, turbot manifest sex dimorphism difference during hypoxia stress-induced hematological and biochemical response.