The elusive kegani: why this hairy crab is a prized Japanese culinary treasure

Nature · Published 3 October 2026 Swipe more like this →

In short: Known as kegani, the horsehair crab is a staple of Japanese cuisine, yet it remains a biological enigma. Thriving in the frigid, sandy depths of the Northwest Pacific, this crustacean is defined by its soft, spine-covered shell and a life cycle that is intricately tied to the rhythm of the sea.

Erimacrus isenbeckii, commonly referred to as the horsehair crab, inhabits the sandy benthic zones of the Northwest Pacific, particularly around the Hokkaido coast, the Sea of Okhotsk, and the Western Bering Sea. These crabs are well-adapted to cold environments, with males typically residing in waters around 3.4 °C at depths of 66 meters, while females prefer slightly cooler temperatures of 2.4 °C at depths of 64 meters. They are substantial creatures, with adult carapaces reaching 100 to 120 mm in length and total body weights exceeding 1 kg.

The species' life cycle is a slow, temperature-dependent process. Females attach their eggs to their pleopods, and the incubation period is estimated to last over a year. Hatching occurs between March and May, perfectly timed with the spring phytoplankton bloom in the Sea of Okhotsk. During this early phase, the larvae exist as zooplankton before settling on the seafloor by July. Once mature, these crabs exhibit distinct behaviors, including a high frequency of feeding—three to four times every ten to twelve hours—and a notable tendency toward cannibalism during the spring months.

Despite its status as a vital commercial species in Japan, scientific understanding of the horsehair crab remains specialized and somewhat limited. The fishery has seen significant fluctuations; after peaking at 27,000 tons in the 1950s, annual catches dropped to 2,000 tons by 2003. This decline has necessitated the implementation of various stock enhancement programs to preserve the population. Because the species is found at depths up to 350 meters, studying its development and population dynamics presents ongoing challenges for researchers attempting to balance commercial demand with ecological sustainability.

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