Evaluation of hypoxia tolerance in F3 hybrids of blunt snout bream (Megalobrama amblycephala) x topmouth culter (Culter alburnus)

To compare gill hypoxia adaptation mechanisms, the hypoxia-related physiological indices were measured in F-3 self-crossing population of blunt snout bream (Megalobrama amblycephala)female x topmouth culter (Culter alburnus)male hybrids. The critical oxygen pressure (P-crit) of F-3 population was 28.33 +/- 1.58 Torr, which is higher than topmouth culter (21.69 +/- 0.85 Torr) and lower than blunt snout bream (33.00 +/- 0.97 Torr). Moreover, the lower oxygen tension threshold for loss of equilibrium (LOEcrit) of F-3 hybrids was 1.09 mg.L-1 higher than topmouth culter (0.91 mg.L (1)) and lower than blunt snout bream (1.30 mg.L (1)). These results indicated that the hypoxia tolerance of F-3 hybrid fish was significantly higher than that of blunt snout bream. In the hypoxic environment, gill remodeling reactions increased the mass-specific lamellar area. In this study, gill remodeling was observed in blunt snout bream, topmouth culter and F-3 hybrids. However, a particularly intriguing finding was that the gill recovery ability of F-3 population was better than that of blunt snout bream after reoxygenation treatment. This might be related to the capability of physiological and biochemical regulation and lactic acid excretion of F-3 hybrids. Together, these results showed that the F-3 population inherited the gill remodeling mechanism of their parents, which had better hypoxia tolerance than blunt snout bream, and they could change the morphology and physiological and biochemical levels of gill tissue to cope with hypoxia.