Effect of low dissolved oxygen on the oxygen consumption rate and rhythm of the mudskipper Scartelaos gigas (Pisces, Gobiidae)

Abstract

The mudskipper Scartelaos gigas is expected to experience repeated severe hypoxia in its environment. Hence, we conducted experiments on the oxygen consumption rate (OCR) and OCR rhythm of S. gigas at low graded dissolved oxygen (DO) levels, without access to atmospheric air, to estimate its tolerance to hypoxia. A dominant circadian OCR rhythm was observed at the control DO level of 6.96-7.78 mg O-2/l. This rhythm was unchanged until 2.06 mg O-2/l, even though the amplitude of the peak was somewhat diminished at 2.06-2.87 mg O-2/l. The OCR rhythm amplitude was greatly diminished and the rhythm period was also greatly changed at 1.23-2.05 mg O-2/l. Nevertheless, the mean OCR (0.11 ml O-2/g WW/h) at 1.23-2.05 mg O-2/l was similar to that of control (0.12 ml O-2/g WW/h). Thus, the weakness and period change of the OCR rhythm kept the metabolic rate level similar to control. These results suggest that S. gigas does not have normal metabolic activity at 1.23-2.05 mg O-2/l but barely manages to endure this DO level as a pre-emergency state. This species could be inhibited under a longer maintenance period at DO level of 1.23-2.05 mg O-2/l or still lower. It can be concluded that S. gigas is quite tolerant to low DO environment and may have a specific strategy for such tolerance.