We report a sudden explosive rise in abundance off southeastern China of a fish species that is hypoxia-tolerant, Bombay duck (Harpadon nehereus, Family Synodontidae), belonging to an Order (the Aulopiformes) encompassing overwhelmingly deep-sea fishes, but which predominantly occurs in coastal water. We suggest that this is made possible by the very high water content of its muscle and other tissues (about 90%, vs 75–80% for other coastal fish), which reduces its oxygen requirements and allows it to outcompete other fish in low-oxygen neritic and estuarine waters. We suggest that the extent to which this drastic shift in abundance and in the resulting community structure in a very extensive and extremely important coastal marine ecosystem offer evidence of growth of ocean deoxygenation along the western edge of the North Pacific Ocean. Also, we suggest that this episode may represent an instructive example of similar disruptions of established marine biological community structures and interlinked life support and natural resource systems that may be expected to emerge under current global trends of climate/environmental change.