The ultimate state of lying flat: eating once a year and taking a shit once a year

I often see people joking online that deep-sea creatures can grow whatever they want because nobody watches them, but it is a mystery that they can look like movie stars and still be popular. Previously, I introduced the frilled shark that became the prototype of "Godzilla's second form". This time, I will talk about the giant isopod (Bathynomus giganteus) that looks like an "Imperial Stormtrooper", has sharp eyes and is covered in armor.

There are about 20 species of Bathynomus in the western Atlantic, western Pacific, and Indian Oceans, from tropical to temperate waters. The epithet giganteus comes from the Latin word for "gigantic," and it is not difficult to infer from the Chinese name "big king" that its size is top-notch among its genus peers, with an average body length of more than 17 cm and a maximum of 50 cm. Large individuals can weigh more than 1 kg and nearly 2 kg.

Giant isopod | Corbari L. / Wikimedia Commons

Stormtrooper from Star Wars | big-ashb / Wikimedia Commons

The "star" who has been on hunger strike for five years

Giant isopods live mainly in the dark, soft, sandy seabed at a depth of 200 to 1,000 meters in the Gulf of Mexico and the western Atlantic Ocean. As "sea scavengers", they mostly feed on the carcasses of large fish and even whales that fall to the bottom of the sea. With their armored bodies, people initially believed that they crawled slowly on the seabed with seven pairs of sturdy jointed limbs on their abdomens. Until November 30, 2017, an unmanned submersible of the National Oceanic and Atmospheric Administration (NOAA) of the United States filmed the giant isopods swimming at a depth of about 800 meters in the Gulf of Mexico. They looked as light as flying, just like the half-foot-long mantis shrimp we are familiar with.

Giant isopods can also swim flexibly | oceanexplorer.noaa.gov

How could such a novel and interesting deep-sea creature not attract the attention of researchers and deep-sea aquariums? Especially several aquariums in Japan that have experience in breeding deep-sea creatures. After all, in the south of Suruga Bay in central Honshu, Japan, at a depth of 150-600 meters, there live giant isopods (B. doederleinii) of the same genus.

Unfortunately, the giant isopods, which are 10 to 15 cm long, are easily caught in the fishing trawls of Japan, a seafood powerhouse, and are even taken for development and cooking. The popularity of the giant isopod is much higher, as can be seen from various giant isopod backpacks, giant isopod cup noodle covers, gashapon toys, and even mobile games that collect giant isopods (such as the famous Animal Crossing). It can be said that they are of the same genus but have different fates, which is a pity. By the way, some people in China also eat giant isopods. Restaurants in Sai Kung, Hong Kong, once sold giant isopod dishes.

Model of giant isopod from Toba Aquarium | x768 - Toba Aquarium / Wikimedia Commons

Among the aquariums that raise giant isopods, the most famous one is Toba Aquarium in Toba City, Mie Prefecture, Japan. Toba Aquarium has been raising giant isopods from the Gulf of Mexico since September 2007. As of July 2021, there are 34 records of raising them. The longest record is No. 14, which has been raised for 2,825 days. There are currently 5 living ones. In the process of artificial breeding over the past decade, the aquarium has recorded and photographed many little-known behaviors of giant isopods.

Among the 34 giant isopods kept in Toba Aquarium, the most famous one is the No. 1 one that "died after five years of fasting". After entering the aquarium in September 2007, it only ate once in 2009. After that, the giant isopod remained unmoved by the various delicacies such as squid and fish put in by the breeder. It was confirmed dead on February 14, 2014, Valentine's Day in the heavy snow. The most amazing thing is that this giant isopod was not as skinny as people imagined due to fasting. When it was confirmed dead, it weighed 1060 grams, which was almost the same as when it first entered the aquarium. After the autopsy, no inflammation or discolored parts of the digestive tract were confirmed. The cause of death is still unknown.

Scientific illustration of the giant isopod | Biodiversity Heritage Library / Flickr

Losing freedom, not wanting to grow up

Does it mean that the giant isopod loses its appetite when it leaves the huge water pressure and the dark and cold environment of the deep sea where you can't see your claws? Not really. Although other artificially raised giant isopods are also like ascetics who "practice fasting", there are still records of eating a small amount every few years. Researchers believe that "eating one meal for three years" is the way giant isopods adapt to the "food shortage" in the deep sea - slow metabolism.

The supporting evidence of "slow metabolism" is that the aquarium occasionally collects feces from giant isopods that have been "constipated for several months or even more than a year" in the breeding tank. The giant isopods in Toba Aquarium even made the news when they went to the toilet, which shows how slow their metabolism is (and why the Japanese media made a fuss about it).

Giant isopods eating at Oita Aquarium | livedoor news / youtube

What surprised the researchers even more was that the feces of the giant isopods contained not only fish bones, fish scales, and sponge-like fibers, but also household garbage such as plastic, rubber, and paper scraps. These garbage were obviously not fed by aquarium keepers, but were ingested by the giant isopods in the deep sea before being fished out. The human household garbage eaten by the "sea scavengers" not only proves the omnivorous nature of the giant isopods, but also provides irrefutable evidence that human waste affects the deep-sea environment.

Giant isopod specimen | Eric A. Lazo-Wasem - Gall L / Wikimedia Commons

The giant isopod has a slow metabolism, so its growth rate is also slow. Like its soft-shelled companions such as lobsters and mantis shrimps, the giant isopod also undergoes molting during its growth. Judging from the molting habits of giant isopods of the same genus, when the giant isopod molts, it starts to shed its old shell from the fifth segment of the thorax, which is the back half of the body, and then sheds from the front half after the back half of the body gradually regains its hardness. There have been 4 cases of artificially raised giant isopods molting in Japan and 1 case in the United States, but unfortunately, these giant isopods that shed the back half of their old shells did not successfully shed the front end and died suddenly.

According to past breeding records, when male giant isopods grow to about 29 cm, they will grow a pair of rod-shaped copulator for sperm output from the inner side of the second abdominal limb after molting, reaching the sexual maturity stage suitable for reproduction. In contrast, females are quite "precocious", with a paper reporting that a female individual reached sexual maturity at 16.5 cm. Toba Aquarium once dissected a dead female individual with a body length of 15.5 cm and observed that its ovaries were well developed, with the diameter of the egg cells reaching 5-7 mm. Sexually mature female giant isopods will swell in the 1st to 5th abdominal limbs after molting, forming an ovulation plate to protect the eggs.

Large isopod kept in an aquarium | Daiju Azuma / Wikimedia Commons

The giant isopod has successfully hatched from fertilized eggs to larvae in an artificial breeding environment, but the poor giant isopod still faces many difficulties in survival, and attempts at artificial breeding are even more out of reach.

With the development of deep-sea submersibles and the progress of ocean-related science, more and more deep-sea creatures will gradually come into people's view. There are countless unsolved mysteries and unpredictable ecological value in them. After a brief understanding of the giant isopod, I hope everyone can consciously reduce the generation of garbage in daily life and try to avoid garbage entering the sea, so as to prevent the deep sea from becoming a garbage dump for humans and causing the "sea scavengers" to face the problem of indigestion.

Giant isopods kept in aquariums | Chino youko

This article comes from the Species Calendar, welcome to forward