Project to approach the ecology of the horsehair crab — New technology expected for efficiency enhancement of growth and reproduction

The horsehair crab is a large cold-water crab species that is widely distributed in Japan from the Sea of Okhotsk to the Pacific coast and the Sea of Japan coast. While it is an important representative fisheries species of Hokkaido, catch volumes have significantly decreased. Therefore, Hokkaido has established rules allowing only the catching of males with a carapace length of 8 centimeters or more to promote recovery of resource abundance. Among areas in Hokkaido, Oshamambe Town, which encompasses Funka Bay, is renowned as a specialty production area for horsehair crab, but horsehair crab catch volumes have been declining in recent years.

A horsehair crab research team centered around Professor Ken Takeuchi of Tokyo University of Science Oshamambe Division, with Assistant Professor Kenji Toyota from the Graduate School of Integrated Sciences for Life at Hiroshima University, Professor Tsuyoshi Ohira from Kanagawa University, and others, has been implementing a project to elucidate the mechanisms of horsehair crab growth and reproduction, and has now discovered a blood glucose regulatory factor in horsehair crabs. This was published in General and Comparative Endocrinology.

Decapod crustaceans (crabs, shrimp, and hermit crabs), to which horsehair crabs belong, possess eyestalks that support protruding compound eyes, and within these eyestalks is tissue called the sinus gland that produces and secretes hormones. These eyestalk hormones play important roles in crustacean growth and reproduction, including body color regulation, and research has long been conducted on domestically and internationally important fisheries species such as sakura shrimp and kuruma shrimp. However, no research on eyestalk hormones had been conducted on horsehair crabs, and the mechanisms of growth and reproduction controlled by eyestalk hormones remained unclear.

The research team extracted sinus glands from the eyestalks of fresh horsehair crabs that had just been landed and analyzed the eyestalk hormones using liquid chromatography and RNA sequencing. Additionally, to clarify the function of isolated and purified eyestalk hormones, in vivo experiments using living horsehair crabs are essential. This is because hormone functions are closely related to internal organs and metabolic systems, and to accurately evaluate their functions, verification in living organisms where whole-body responses can be confirmed is indispensable. However, horsehair crab rearing requires breeding facilities that can use abundant chilled seawater, making rearing itself difficult. Therefore, as an alternative method to experiments using living horsehair crabs, the team conducted physiological experiments using blue swimming crabs of the family Portunidae, which are easy to obtain and rear.

Since the research also aimed to search for hormones related to reproduction in male and female horsehair crabs, they proceeded with the search for eyestalk hormones from the sinus glands of both males and females. The results of reverse-phase liquid chromatography of sinus gland extracts showed that the composition of eyestalk hormones from males and females were very similar, with two large peaks commonly detected in both sexes. When one of these large peaks was extracted and its mass and amino acid sequence examined, the properties of the hormone became clear. Furthermore, RNA sequence analysis revealed the nucleotide sequence of this hormone.

From these results, it was found that this hormone is a crustacean hyperglycemic hormone (CHH) that commonly acts to maintain glucose concentration homeostasis in the blood of crabs and shrimp; the researchers named it purified CHHa (EiCHHa). Since CHH has been reported to have hyperglycemic effects in other crustaceans, they investigated whether EiCHHa also has hyperglycemic effects. However, since it is difficult to use living horsehair crabs in experiments, they instead used blue swimming crabs, which are closely related to horsehair crabs and easier to rear.

When blue swimming crabs with both eyestalks removed were reared for two days without feeding, their blood glucose levels dropped significantly. When EiCHHa was injected into blue swimming crabs in this state, blood glucose levels rose significantly after two hours. On the other hand, no changes were observed in the group that received only physiological saline injections. This revealed that EiCHHa also has hyperglycemic effects like other CHHs, and furthermore that horsehair crab eyestalk hormones can be analyzed using blue swimming crabs.

The mechanisms of horsehair crab growth and reproduction are still shrouded in mystery. In this research, the team succeeded in organizing basic information for horsehair crab hormone research and establishing alternative physiological experimental methods using blue swimming crabs that do not rely on horsehair crabs. In the future, they aim to utilize this information and experimental technology to develop new technologies aimed at promoting horsehair crab growth and enhancing reproductive efficiency.

Journal Information
Publication: General and Comparative Endocrinology
Title: Characterization of a crustacean hyperglycemic hormone of the horsehair crab Erimacrus isenbeckii
DOI: 10.1016/j.ygcen.2025.114777