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Site opening on 19 December 2023
Visions
Perhaps, none is more visionary than sturgeon research, which began in the 1990s at the Laboratory of Aquaculture Biology, Faculty of Fisheries, Hokkaido University. The series of research has been not only from the perspective of increasing the number of caviar-bearing females, but also from the perspective of developing technologies for waste-free utilization of marine resources with a focus on collagen and advanced aquaculture management for a more sustainable future in tune with society's needs. This research is currently one of the most significant research projects in the Faculty of Fisheries Sciences, Hokkaido University. At this time when sturgeon are in season, we will provide a hot topic on one aspect of sturgeon research, especially the advancement of aquaculture management and the advanced utilization of previously unused parts of sturgeon. We also hope to reintroduce the Mikado Sturgeon, which is believed to be extinct in Hokkaido, and will provide updates on any related research in the future.
FoM Editorial
19 December 2023 posted
Taxonomy and Morphology of Sturgeon
Sturgeon, the current theme of FoM, are classified into the class Osteichthyes, subclass Actinopterygii, infraclass Chondrostei and order Acipenseriformes, and 27 species in two families and six genera are recognized as extant species (Nelson et al., 2016) (Table). Because sturgeon are known as “Chou-zame” in Japan (“zame”, derived from “same” meaning shark in Japanese), some Japanese may consider that sturgeon are a kind of shark. Indeed, the head of sturgeon is slender anteriorly (but paddlefish have a different snout morphology as mentioned below), and the mouth is situated on the lower surface of the head, as in sharks (Fig. 1). However, sharks are included into the class Chondrichthyes, and sturgeon and sharks are situated on different phylogenetic positions (Fig. 2). Accordingly, sturgeon are not kinds of shark and their morphological similarity is simply a result of convergent evolution.
Sturgeon possess common morphological characters such as scales ganoid, single dorsal and anal fins, both situated on the posterior portion of the body, the shoulder girdle, a series of bony elements supporting the pectoral fin, including the clavicle, caudal fin heterocercal, and intestines with spiral valve. Sturgeon have a larger number of cartilaginous parts than generalized bony fish, but they also possess many bony elements. This is also different from sharks because sharks have only cartilaginous bony parts. Bony fish including sturgeon have one gill opening on one side of the head, but sharks usually have five (or more rarely six or seven) gill openings. This is also a useful character to help distinguish between sturgeon and sharks.
Sturgeon are divided into two families Polydontidae and Acipenseridae. The family Polydontidae includes two species; Paddlefish known from the Mississippi drainage area in the U.S. and Chinese paddlefish from the Yangtze River, some other rivers and adjacent sea in China. The most characteristic feature of Polydontidae is the long, plate like and wide snout. The name of Paddlefish of this family is considered to be derived from this feature. This family also has characteristics such as the lower side of the snout having two short barbels and a body without the large scales of acipenserids. Paddlefish reach up to 1.5 m body length and 80 kg body weight. Although it is said that Chinese paddlefish reach 7 m in total length, the longest measured record is 3 m.
The family Acipenseridae includes 25 species in four genera, found in fresh water, brackish lakes and coastal regions in middle to high latitudes in the northern hemisphere. Acipenseridae shows morphological characteristics such as the body with scales arranged in five rows, the lower side of the snout having four long barbels. Acipenseridae is the largest class in the body size among freshwater fish and is known for its longevity. A Beluga specimen captured in 1926 was 1000 kg body wight and was estimated to be 75 years old at least. Another reliable record, 3.8 m total length and 580 kg body weight, is also known in a specimen of White Sturgeon caught in 1912.
Sturgeon are in danger of extinction because of overfishing and habitat destruction (below Table). According to Red List of International Union for Conservation of Nature (IUCN), Chinese Paddlefish have already become extinct and Yangtze Sturgeon have become extinct in the wild. Of the remaining 25 species, 17 species are classed as “Critically Endangered”, the highest rank of danger of extinction, 3 species are classed as “Endangered”, the next rank, and 5 species are classed as “Vulnerable”. Of the 25 species, the number of individuals is increasing in only two species (Adriatic Sturgeon and Atlantic Sturgeon) and stable in only three species (Shortnose Sturgeon, Shovelnose Sturgeon and White Sturgeon), but it is decreasing in other 17 species.
Background photo. Comparison of sturgeon (Acipenser gueldenstaedtii: upper) and shark (Squalus suckleyi: lower) (photos and specimens deposited in Hokkaido University Museum)
Backgound tree: Major phylogenetic relationships of fishes (based on Nelson et al., 2016).
Table Classification of 27 species of sturgeons
Polydontidae
Paddlefish Polyodon spathula（VU）
Chinese paddlefish Psephurus gladius（EX）
Acipenseridae
Siberian sturgeon Acipenser baerii（CR）
Shortnose sturgeon Acipenser brevirostrum（VU）
Yangtze sturgeon Acipenser dabryanus（EW）
Lake sturgeon Acipenser fulvescens（EN）
Russian sturgeon Acipenser gueldenstaedtii（CR）
Green sturgeon Acipenser medirostris（EN）
Sakhalin sturgeon Acipenser mikadoi（CR）
Adriatic sturgeon Acipenser naccarii（CR）
Ship sturgeon Acipenser nudiventrtis（CR）
Atlantic sturgeon Acipenser oxyrinchus（VU）
Persian sturgeon Acipenser persicus（CR）
Sterlet Acipenser ruthenus（EN）
Amur sturgeon Acipenser schrenckii（CR）
Chinese sturgeon Acipenser sinensis（CR）
Stellate sturgeon Acipenser stellatus（CR）
European sturgeon Acipenser sturio（CR）
White sturgeon Acipenser transmontanus（VU）
Kaluga Huso dauricus（CR）
Beluga Huso huso（CR）
Syr-Darya shovelnose Pseudoscaphirhynchus fedtschenkoi（CR）
sturgeon
Small Amu-Darya Pseudoscaphirhynchus hermanni（CR）
shovelnose sturgeon
Amu-Darya shovelnose Pseudoscaphirhynchus kaufmanni（CR）
sturgeon
Pallid sturgeon Scaphirhynchus albus（CR）
Alabama sturgeon Scaphirhynchus suttkusi（CR）
Shovelnose sturgeon Scaphirhynchus platorynchus（VU）
EX, Extinct; EW, Extinct in the Wild; CR, Critically Endangered; EN, Endangered; VU Vulnerable
IMAMURA Hisashi ・Faculty of Fisheries Sciences, Hokkaido University・Professor / the Fisheries Science Center, the Hokkaido University Museum・Director
References
IUCN (2023) The ICUN Red List of threatened species, version 2022-2.
Matsuura, K. (ed.) (2007). The new encyclopedia of aquatic life 2. Fishes I. Asakura Publishing Co., Ltd., Tokyo (in Japanese).
Nelson, J. S., T. C. Grande and M. V. H. Wilson. 2016. Fishes of the world, 5th edition. John Wiley & Sons, Inc., Hoboken, New Jersey.
Yabe, M., T. Kuwamura and Y. Takagi (2017) Ichthyology. Kouseisha-Kouseikaku Co., Ltd., Tokyo (in Japanese).
19 December 2023 posted
Sturgeon in Japan
Some people may be surprised to learn that Japan used to have native wild sturgeon. Caviar is made from the ovaries of sturgeon, and most of the caviar consumed in Japan today is imported from Russia, Europe, and the Middle East. This fact may lead to a vague perception that sturgeon is only a European or Russian fish. However, sturgeon were also once present in Japan. Takeshiro Matsuura, the Hokkaido explorer from the end of the Edo period to the early Meiji period and godfather of Hokkaido, wrote in his Teshio Nisshi, one of his expeditions, that many sturgeon would approach boats crossing the Teshio River with their snouts raised. It seems that sturgeon were once a common sight in Hokkaido's rivers. As far as I know, the last recorded sighting of wild sturgeon in a river in Hokkaido was at Kamuikotan, on the Ishikari River in the late 1950s. There are more than 20 species of sturgeon in the world, but what kind of sturgeon is the one Matsuura described here?
It is the Sakhalin Sturgeon (Acipenser mikadoi, the Mikado sturgeon is the Japanese name). The standard Japanese name for this species is "sturgeon," but since there are many different species of sturgeon in the world, we will refer to it by the name "Mikado sturgeon. The name "Mikado" comes from the scientific name Acipenser mikadoi, which was first used by the German zoologist Dr. Hilgendorff to describe sturgeon in Hokkaido in 1892. It is truly regrettable for the Japanese that Dr. Hilgendroff went to the trouble of giving the Mikado a wonderful name, only for it to become extinct in the wild in Hokkaido.
However, there are still wild Mikado Sturgeon outside Hokkaido. Although the spawning lineages in the Teshio and Ishikari Rivers have disappeared, several pairs are still reported to spawn annually in the Tumnin River in Russia's Maritime Province. According to past surveys, the Mikado Sturgeon spawned in the Tumnin River spend three or four years as juveniles in the river, then migrate to the sea where they grow. They probably return to the Tumnin River to spawn when they reach puberty after about 10 to 15 years, but the Mikado Sturgeon that migrate around Hokkaido are sometimes caught in fixed nets. Hokkaido University has asked fishery cooperatives throughout Hokkaido to contact them when sturgeon are caught, and has collected a considerable number of wild sturgeon over the past 30 years. At present (2023), there are five surviving Mikado Sturgeon collected by Hokkaido University and affiliated organizations. We would like to increase the number of these sturgeon. In the future, we hopes to return some to the Teshio River, which was once teeming with sturgeon.
In addition to the Mikado, two other species of sturgeon spawn in the Amur River (Heilongjiang River) in the northern Pacific. They are the Kaluga Sturgeon and the Amur Sturgeon. These two species spawn in the Amur River, and the hatchlings spend several years in the Amur River before moving to the ocean. After reaching the sea, they migrate around the waters of Sakhalin and Hokkaido for more than 10 years, and are occasionally caught in fixed nets in Hokkaido. In other words, three species of sturgeon may be caught in Hokkaido: Mikado, Kaluga, and Amur. While a few Kaluga are caught every year, Amur and Mikado are rare, with specimens only one being caught every few years or so. Although both species are endangered, several Kaluga Sturgeon have been caught continuously in recent years, and the population may be stable at a fixed abundance. An environment that maintains continuous spawning is considered important for the maintenance and recovery of the population, but the Timnin River is a river in a large forested area inhabited by Amur Tigers, and it is difficult to believe that the spawning environment has deteriorated in the modern era. In this light, it is conceivable that the extinction of the species in Hokkaido's rivers has had a major impact on the dramatic decline in the numbers of the Mikado Sturgeon.
IJIRI Shigeho・Faculty of Fisheries Sciences, Hokkaido University・Associate Professor
19 December 2023 posted
Sturgeon Breeding
Mature eggs and sperm are required for fish breeding. In order for the oocyte to develop into a fertilizable "egg," the oocyte must undergo "vitellogenic growth," in which the yolk accumulates in the oocyte and the oocyte diameter is greatly enlarged. When vitellogenesis is sufficiently advanced and the spawning environment is ready, "oocyte maturation" is triggered, in which meiosis of the oocyte resumes, followed by its release from the follicular cell layer surrounding it (ovulation), (For details, please refer to the chapter "Regulatory Mechanism of Egg Maturation-Induced Steroid Hormone (MIS) Production from Cherry Salmon" in Fish of the Month, Salmon & Trout). In sturgeon, oocyte maturation and ovulation do not occur spontaneously in captivity, although vitellogenesis does progress. Therefore, we periodically conduct biopsy ovarian samples throughout the year and culture the ovarian follicles to test their ability to mature and ovulateion. In individuals that are determined as capable of inducing oocyte maturation and ovulation, luteinizing hormone-releasing hormone (GnRH) is injected to stimulate the release of luteinizing hormone (LH) from the pituitary, artificially inducing oocyte maturation and ovulation. Once ovulation is confirmed, the eggs are promptly squeezed out by abdominal pressure for artificial insemination. This method of inducing spawning in sturgeon with GnRH is mainly used in the Middle East, while in Europe, the mainstream method seems to be to directly inject carp pituitary homogenate (containing carp LH) instead of GnRH. This method of inducing spawning by hormone injection is called artificial maturation. If there is an abundance of parental fish, we can inject GnRH into a large number of female parental fish, and if even a few of them spawn, there will be sufficient production of fry (seedling production), but in most cases, the number of female parental fish is limited, so in order to increase the probability of successful spawning induction as much as possible, it is important to accurately determine the stage of oocyte development. Especially in the case of sturgeon, there are many cases where oocyte maturation can be induced but ovulation is not achieved. It is difficult to accurately determine the ovulatory competence of sturgeon using only empirical intuition and culture assays, and we are currently conducting research into the molecular mechanisms that lead to ovulation in sturgeon (Surugaya et al. 2022; 2023). Once the molecular mechanism of ovulatory potential is understood, we believe it will be possible to determine more accurately whether or not a sturgeon is capable of ovulation by examining the expression of a group of genes related to ovulation prior to GnRH injection. In males, spermiation can also be induced by injecting GnRH. Artificial maturation of male parent fish is not as difficult as in female parent fish, and in most cases, injecting several sturgeons will almost certainly result in highly active sperm.
The first successful seedling production of the Kaluga sturgeon was achieved in 2007. A large number of Kaluga sturgeon are still being raised, and we expect that caviar production from Kaluga sturgeon will be realized in 10 years or so. Since a large number of parent fish of Kaluga sturgeon have been cultured, it may become a major aquaculture species in the next 20 to 30 years. The first successful seedling production of the Mikado sturgeon was achieved in 2008. However, the Mikado sturgeon is difficult to raise in captivity, and all of them have now died. There are a few parent fish of the Mikado sturgeon, so it is difficult to get a chance to induce spawning. We hope that the next time we succeed in producing seedlings, we will be able to ensure their growth (Hokusui Books: Science of the Whole Sea, Southern Hokkaido Fish Guide).
Finally, I would like to introduce the current status of sturgeon aquaculture. Sturgeon are being farmed in many parts of Japan, and in most cases, the seedlings used for sturgeon farming are supplied by Fujikin, Inc. The main species supplied by Fujikin are the Bester sturgeon, Siberian sturgeon, and Sterlet sturgeon, of which the former is the most widely cultivated. Bester sturgeon is a hybrid between Beluga sturgeon and Sterlet sturgeon. Beluga has large egg diameters and is considered to produce finest caviar, but it must be raised for more than 15 years before caviar can be harvested. On the other hand, the Sterlet sturgeon is a small sturgeon with smaller egg size and lower value as caviar, but it has the advantage of being able to produce caviar in 4 or 5 years. Bester sturgeon is widely farmed in Japan because it is a highly efficient species with intermediate egg size and can produce caviar in about seven years. The Kaluga sturgeon is a close relative of the Beluga sturgeon with a larger egg diameter, and the Mikado sturgeon has an even larger egg diameter, both of which have the potential to produce the highest quality caviar. However, the Kaluga sturgeon must be kept in captivity for more than 10 years before caviar can be harvested, and the Mikado sturgeon is intended to be returned to the wild and is not currently intended to be used for food production. In Hokkaido, the Bifuka Town Promotion Public Corporation has established a large-scale sturgeon aquaculture facility and is currently raising large numbers of sturgeon. Currently, caviar is obtained from the Bester sturgeon, but the town has also succeeded in producing seedlings of Amur sturgeon early on, and it is hoped that production of Amur sturgeon caviar will become possible in the near future. The Bifuka Onsen Ryokan in Bifuka Town serves sturgeon cuisine, and the local sturgeon dishes have been well received by guests (background photo: the sturgeon course in The Bifuka Onsen Ryokan). Although the Bester species is currently the main sturgeon species because it takes time to grow, we are still looking forward to the day when Hokkaido sturgeon, Kaluga, Amur, and if they can be reproduced in excess, Mikado sturgeon dishes may be offered in future.
IJIRI Shigeho・Faculty of Fisheries Sciences, Hokkaido University・Associate Professor
References
Surugaya, R., Hasegawa, Y., Tousaka, K., Adachi, S., Ijiri, S. 2023. mRNA expression profiles of proteolytic genes during the process of ovulation in ovarian follicles of sturgeons. Fisheries Sci. In Press.
Surugaya, R., Hasegawa, Y., Adachi, S., Ijiri, S. 2022. Changes in ovulation-related gene expression during Induced ovulation in the Amur Sturgeon (Acipenser schrenckii) ovarian follicles. International Journal of Molecular Sciences, 23:13143.
北水ブックス 海をまるごとサイエンス（2018年初版）、第4章：殖えない魚を殖やしたい、pp.42-54. 海文堂出版.
北水ブックス 道南おさかな図鑑（2023年初版）、ミカドチョウザメ、ダウリアチョウザメ、pp.46-49. 海文堂出版.
19 December 2023 posted
Generating Synthetic Data Set for Smart Sturgeon Farming
Individual identification of sturgeon is beneficial for stock control in breeding tanks or ponds to track the health status of individual fish; however, research is ongoing into the automatic identification and tracking technology of individual sturgeon. There are many species of sturgeon, and their appearance is very similar. In particular, it is not easy to distinguish different species when looking into the tank from the surface of the water. However, the fluctuation of the water's surface and reflections of light make identification of individuals even more difficult. Although deep learning is effective in identification, it is difficult to obtain data sets with sufficient quantity and variation to be used in real-world applications.
Our approach is to automatically generate synthetic data sets from 3DCG simulations. However, the path to individual identification is challenging . First, a deep neural network (DNN) must learn what a sturgeon looks like (detection). Next, the sturgeon's locomotion and pathway must be tracked (tracking). Then, each individually detected sturgeon must be identified (recognition).
Background photo shows a rigged model of a 3DCG sturgeon. The rigged model is a technique widely used in conventional computer graphics animation. The bones and joints are embedded into the 3D model, and the entire body moves when the joints angles change.
Background photo shows the results of fish counting using a deep neural network that has already ‘learned’ using the automatically generated synthetic data sets.
The conventional computer graphics model is enough to learn both detection and tracking applications. However, identification of individual fish is difficult even with deep learning, because of differences in shape as seen from the surface of the water. Therefore, we must change our 3D model from conventional CG to musculoskeletal. The musculoskeletal model is able to generate differences in movement between individuals by generating a detailed musculoskeletal model of a sturgeon (background photo) and simulating muscle movement. This musculoskeletal model was assembled by carefully reproducing in 3DCG each of the actual bones and muscles dissected by Professor Hisashi Imamura of the Faculty of Fisheries Sciences, Hokkaido University. Currently, research is underway to instigate actual movement in the sturgeon musculoskeletal model.
ISHIWAKA Yuko・Softbank Corp.
19 December 2023 posted
Utilization of Sturgeon-By-Products
Sturgeon Is A Luxury Food
Sturgeon roe, or caviar, is one of the world's most famous delicacies, but sturgeon meat is also used as a luxury ingredient in a variety of dishes.
Waste Portions Are Not Garbage; They Are A Rich Resource For Collagen
Unused parts such as the skin, vertebrae and air bladder would have usually been thrown away. As a researcher at Hokkaido University, which advocates the promotion of SDGs, I cannot overlook this.
The usually unused parts of sturgeon contain large amounts of collagen. Humans have long been aware of its value. Around the end of the 16th century, the collagen-rich sturgeon glue was used as a raw material for an agglutinant called ‘icing lath’, which was used as a gold leaf glue in painting and was also used to remove cloudiness in white wine. Icing lath is still used for similar purposes and is one of the most expensive by-products of sturgeon.
In recent years, fish collagen has been increasingly used in biomedical applications such as wound healing, tissue regeneration, and cell culturing. The waste Portions of sturgeon are a promising source of collagen. In addition, it has been reported that degraded sturgeon collagen (collagen peptide) has physiological functions such as hypoglycemic effect (aiding treatment of diabetes), antioxidant effects (suppression of oxidative stress), and anti-inflammatory effects (alleviation of lifestyle-related diseases); These findings highlight the potential of sturgeon collagen as a bio-material supporting human health.
A New Approach to Advanced Utilization
Recently, it was found that antioxidant and anti-inflammatory functions are significantly improved by binding sugar molecules to collagen derived from the spinal cord of sturgeon (Yang et al. 2023). This glycated collagen is created using the Maillard reaction that occurs naturally between food components (responsible for the dark brown color of miso and soy sauce and the browning of toast). Research and development to create new functional materials from sturgeon by-products, such as this example, will contribute to the advanced utilization of sturgeon and the promotion of the aquaculture industry.
SAEKI Hiroki・Faculty of Fisheries Sciences, Hokkaido University・Professor
References
19 December 2023 posted
Donation & Research Collaboration
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