This Giant Isopod Hasn't Eaten in More Than 4 Years Keepers are concerned about 'No. 1' By Evann Gastaldo, Newser Staff Posted Feb 26, 2013 1:04 PM CST Updated Mar 3, 2013 10:27 AM CST 16 comments Comments The fasting giant isopod. (YouTube) (Newser) – A giant isopod at Japan's Toba Aquarium apparently enjoyed the horse mackerel he was fed on Jan. 2, 2009—he downed it in just five minutes and hasn't taken another bite since. Feb. 10 marked 1,500 days since the creature, known simply as No. 1, ingested any food, NPR reports. Even so, he appears to be perfectly healthy, say his keepers, who admit they are worried about his "weakened state" and have tried to entice the so-called "scavenger of the deep" with all sorts of different goodies (like squid tentacles). That nickname is a nod to its diet of dead fish, but little else is known about the crustacean's biology, the Japan Times reports. "Giant isopods are always in a state of semihibernation because they don’t know when they can eat, so they limit their energy on breathing and other activities," a marine ecologist at Mie University explains. "For that purpose they sometimes keep a large amount of fat in their livers, so maybe No. 1 still has a source of energy in its body, and that’s why it still has no appetite." The Times notes that No. 1 lives in artificial seawater that's likely void of plankton, algae, or other organic substances that could be surreptitiously sustaining it.