More than 50 families of crab, numbering thousands of species, thrive in practically all parts of the globe. Most crab species are marine and live in salt water or the brackish waters of bays, lagoons and river deltas. A relatively small number have adapted themselves to completely freshwater life-cycles and even fewer varieties have become solely land-dwelling.

Of the over 200 freshwater crab species found throughout Asia, Japan hosts only two: the sawagani (marsh crab) and the mokuzugani (mitten crab).

The sawagani — written with the character sawa, for marsh or mountain stream, and the character kani, meaning crab — is a true freshwater crab found all over the Japanese archipelago, on the Korean peninsula and the island of Taiwan. The diminutive 3-cm adult sawagani have also been spotted as far away as a lake in Las Vegas, Nev., where the U.S. Geographical Survey reported the first sighting early this year. (The origin of these nonnative crabs was eventually traced back to the tank of a local sushi establishment.)

Sawagani is an odd species that changes sex in their lifetime and that give birth to fully developed live young, rather than partially formed zygotes like most crab species.

The mokuzugani — written with the character for seaweed and the character for crab — is the Japanese relative of the much more pervasive Chinese mitten crab (in Japan called the Shanghai mokuzugani). The references to seaweed and mittens both point to the hairlike bristles that grow on this crab’s legs. Fully grown at 5.5 cm, mitten crabs reproduce normally in brackish seawater but spend the rest of their lives upstream in cool, fresh water. The Chinese version of this small crustacean has successfully established itself across most of Asia, Northern Europe and parts of North America.

Freshwater crab are important environmental markers because they require very clean water to survive. There exists a relatively small secondary market for these crabs in the aquarium trade, but they are mostly sold as for consumption. This is where another role of the freshwater crab must be carefully considered: the role of a pathogen transmitter.

In many parts of the world — specifically Southeast and South Asia as well as Africa — freshwater crab commonly carry paragonimiasis, or lung fluke, a condition that affects over 20 million people worldwide. The parasite only exists in unsanitary conditions and is transmitted to humans only when the crabs are eaten in an uncooked state. In Japan, where freshwater crab such as sawagani are generally raised under strict sanitary conditions and are rarely served raw, there is no problem with this particular parasite.

In Japan, mokuzugani are often salted lightly and then boiled or steamed before being served with a citrus wedge and some kind of a seaweed garnish. They can also be seen in soups where they are generally precooked and then simmered. As with most other food crabs, they are perhaps at their best perhaps when the female is full of delicious roe — in the case of the mokuzugani from September to November.

Sawagani range in color from deep purple to blue to bright crimson. They are a treat all summer long, usually available from late May. Not often seen in local supermarkets, sawagani are sold in larger retail food markets and at any good fish purveyor. As with mokuzugani, sawagani must be cooked thoroughly before being served. These little crab are eaten whole as a rule and are usually fried briefly so the crisp shell and all the legs may be eaten.

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Sawagani no amakara-ni

Ama is sweet, kara is salty and ni is from niru to simmer or braise. In this classic preparation, the little crabs are cleaned and then quickly fried (su-age) before being rinsed with boiling water and then finally simmered with sake, soy and sugar with a pinch of hot chili powder (ichimi). As with any shellfish, only live product should be used, preferably on the day of purchase. If the crabs are dead or have an unpleasant odor, discard.

15 sawagani
oil for frying
hot water
1 cup sake (nihonshu)
3 tablespoons koikuchi shoyu (dark soy sauce)
3 tablespoons sugar
1 tablespoon ichimi

1) Wash the crabs briefly in cool water and set in a colander to drain verywell. (Deep frying could be dangerous if they’re still wet.)

2) In a frying pan, place 5-7 cm of oil and bring to 200 degrees. The oil should bubble vigorously around the tip of a wooden chopstick when inserted to test the temperature.

3) Have five or six cups of boiling water and the colander ready for when crabs are done frying.

4) Place the crabs in the hot oil and fry until almost all bubbles have stopped.

5) Carefully remove the cooked crab to the colander, and over the sink, pour the boiling water over the crabs to remove any excess oil. Let them drain while you prepare the simmering liquid.

6) Place the sake in a large pan and bring to a boil, letting the alcohol ignite and burn off. Add the soy sauce and the sugar.

7) When the soy and sugar are incorporated, reduce the heat and carefully place the crabs in the pan and simmer, sprinkling the chili powder on top.

8) Simmer, shaking the pot gently until almost all of the liquid has evaporated. Remove gently to a plate and serve hot or let cool and serve. Serves four to six.

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