Cardiac performance of Chinese black sleeper (Bostrichthys sinensis) at early stages of development under hypoxic conditions

Cardiac performance of the Chinese black sleeper(Bostrichthys sinensis)was examined at early stages of development (the heartbeat, blood circulation and newly hatched larval stages) under different hypoxic oxygen concentrations. Exposure of the embryos at 25°C to 0.2 mg/l dissolved oxygen (DO) indicated periodic heartbeat at both the heartbeat stage and the blood circulation stage, but it started sooner after exposure at the blood circulation stage than at the heartbeat stage. With the appearance of the gill slits, the tolerance of the newly hatched larvae to hypoxia was improved. The larvae did not display periodic heartbeat at 0.2 mg/L DO, but periodic heartbeat occurred at 0.1 mg/L DO and 0.02 mg/L DO after 23.3±6.2 minutes and 13.2±3.4 minutes of exposure. With exposure of the embryos to hypoxia, the occurrence of periodic heartbeat of excised embryos was earlier than that of whole egg embryos at both the blood circulation and heartbeat stages. These results indicated that the tolerance of embryos to hypoxia decreased with the progress of embryogenesis and suggested that the perivitelline liquid can protect the embryos by conserving oxygen. In this study, we also found that a breakdance performance (an arrhythmic heart beat) occurred in the newly hatched larvae at 0.02 mg/l DO. The breakdance performance lasted about 10 minutes, and then the heartbeat became normal.