Give you some answers. One, it may be death by electric leakage. Second, it is possible that he died of lack of oxygen. Third, the fish died of poisoning. Let's talk about this in detail. Have you ever heard the older generation say that a goldfish died and a jar of fish died? This is a symptom of virus and fish. The fish head is black with blood, and the gills of fish are black and smelly after death. This fish is covered with oil and smells fishy. The water in the fish tank stinks and there is white foam on the surface. This is a viral infection.