I came across the following news report from a few days ago: Staff at Tokyo Sea Life Park are baffled by the deaths of over 150 fish in one of its display tanks. The aquarium has just one surviving fish — a bluefin tuna — left in the giant 30m/98ft Voyagers of the Pacific exhibit that up until December last year held almost 160 fish: bluefin tuna, mackerel tuna and striped bonito. Staff are unable to find out why the population in the tank has suddenly crashed. Only 30 fish were left alive by the middle of January and earlier this week the body of one of the two remaining fish was removed. Investigation is under way, looking at a range of possibilities including lighting, noise and vibration levels, nutrition, and toxins. Computers to monitor both the water and the fish found no abnormalities. "An earlier examination has found some sort of virus among some of the dead fish, but it wasn’t the kind that is usually fatal in fish farms," a spokesman said.