How Long Can a Giant Isopod Go Without Eating?

The Giant Isopod’s Incredible Fasting Record

A giant isopod can survive without eating for over five years — one individual at Toba Aquarium in Japan went exactly five years and forty-three days without consuming a single meal before dying, setting what remains one of the most extraordinary fasting records in the animal kingdom.

What Is a Giant Isopod?

The giant isopod (Bathynomus giganteus) is a deep-sea crustacean and one of the largest isopods on Earth, capable of growing up to twenty inches long and weighing several pounds. Related to common pill bugs and beach hoppers, it is an example of deep-sea gigantism — a phenomenon where organisms in the deep ocean grow far larger than their shallow-water relatives. Visually, it resembles an oversized roly-poly bug, with a hard segmented shell, large compound eyes, and seven pairs of legs.

These animals live at depths of roughly 550 to 7,000 feet below the ocean surface, in near-freezing temperatures, total darkness, and crushing pressure. Despite those extreme conditions, they are thriving animals — not relics. They have been documented by researchers, kept in aquariums, and studied extensively by marine biologists.

Built to Devour, Evolved to Wait

The giant isopod is a scavenger and occasional predator. It is equipped with four sets of jaws that work simultaneously, allowing it to rapidly consume carcasses that sink from the ocean above — whale falls, dead sharks, fish, and squid. When food arrives, it feeds aggressively and completely, sometimes eating so much it can barely move.

But food rarely arrives. The deep seafloor is one of the most food-scarce environments on the planet, and giant isopods have evolved a physiological response that is still not fully understood by science: they can enter an extreme low-metabolism state and simply stop requiring sustenance for extraordinary periods. Their bodies appear to slow nearly all energy expenditure, drawing on fat reserves accumulated from previous feasts.

The Story of Number One

The most documented case of giant isopod fasting comes from Toba Aquarium in Japan, where a specimen designated only as “Number One” was kept in captivity beginning in 2007. Staff offered it food consistently. It refused. For five years and forty-three days, Number One consumed nothing — no fish, no shrimp, no offered carcass. Scientists monitored it throughout. It remained alive and appeared physically stable for the duration.

In February 2014, Number One died. The cause was not definitively identified as starvation, and researchers noted it had shown no obvious signs of distress in its final period. The case remains one of the most cited examples of extreme animal fasting in scientific and popular discussions of deep-sea biology.

Why Does This Matter?

The giant isopod’s fasting ability isn’t just a curiosity — it raises serious questions about metabolic biology, energy storage, and what the limits of survival actually are. Understanding how these animals regulate hunger, pause digestion, and preserve muscle and organ function without food intake could have implications for research into metabolism, hibernation biology, and long-duration survival in extreme environments.

The deep ocean still holds enormous gaps in human knowledge. Giant isopods are one of its better-documented residents, yet the mechanisms behind their fasting endurance remain only partially explained. They are a reminder that some of the most biologically extreme life on Earth lives not in space or in textbooks — but miles beneath the surface of the ocean we have sailed for thousands of years.