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Site opening on 31 March 2023
EYES
We are pleased to present the contents of Soi & Mebaru, the fish that heralds the spring season. As you may notice from the photos in this article, these fish have very noticeable distinctive eyes. Since the catch of these fish has been on steadily declining, discreet research has been undertaken to cultivate them. The team of Associate Professor TODO Takashi and Associate Professor HIRAMATSU Naoshi, who are leading the Soi & Mebaru aquaculture project at the Faculty of Fisheries Sciences, Hokkaido University, have summarized the latest research trends. Both of them are known as experienced anglers. They have also provided us with a photo of a beautiful fishprint that has been passed down from one generation to the next, so please keep your eyes peeled to find it.
Welcome photo is a young individual of a hybrid of Kitsune-mebaru and Kuro-soi created by their research group. It is expected to be a new hybrid species that will compensate for the weaknesses of the Kuro-soi & Kitsune-mebaru, such as slow growth and inconsistent evaluation on taste. It is a good candidate to lead Soi & Mebaru aquaculture. In particular, the eye is distinctive as mentioned above.
Soi & Mebaru are one of those fish species that seems to be difficult to classify, as happens when a hybrid appears. Kitsune-mebaru? Tanuki-mebaru? How we can identify??? Professor IMAMURA Hisashi, a leading expert in fish classification at Faculty of Fisheries Sciences, Hokkaido University has also written to us regarding the classification of Soi & Mebaru. Soi & Mebaru used to be common but currently are becoming one of the most important fish in Japan. We hope you will enjoy these new contents.
FoM Editorial
31 March 2023
Tale on Names of Sebastes
Soi and Mebaru, being the current monthly theme of FoM, are general names of fish species belonging to the scorpaeniform sebastid genus Sebastes. Sebastes is a group showing primitive characteristics among scorpionfish. For example, the genus has a poorly-developed suborbital stay. The suborbital stay is a typical characteristic of Scorpaeniformes. The stay is formed on the third infraorbital, one of bony elements of the infraorbital series surrounding the eye. In Sebastes, the posterior end of the suborbital stay is pointed, and separated from the preopercle situated posterior to the third infraorbital or loosely attached with it (Imamura, 2002). In this section, as an introduction to Soi and Mebaru, I will discuss the names of species in the genus Sebastes (this text shows only Japanese names. See Table for scientific names).
About 100 species in the genus Sebastes are known around the world (Love et al., 2002) and 32 species in Japanese waters (Motomura, 2022). Of the Japanese species, 5 species, Gomasoi, Murasoi, Ōgon-murasoi, Kurosoi and Shimazoi, are named soi (or zoi). Murasoi was previously recognized as either being a single species (Amaoka, 1984) or separated into four subspecies, Murasoi, Ōgon-murasoi, Hoshinashi-murasoi and Akabuchi-murasoi (Nakabo and Kai, 2013), but these have all recently been separated into two distinct species Murasoi and Ougon-murasoi; Hoshinashi-murasoi and Akabuchi-murasoi are now recognized as being the same species as the former and latter, respectively (Kai and Nakabo, 2013).
On the other hand, the following 14 species all are known as Mebaru: Aka-mebaru, Shiro-mebaru, Kuro-mebaru, Yoroi-mebaru, Yanagi-mebaru, Togotto-mebaru, Kataboshi-aka-mebaru, Kōrai-yoroi-mebaru, Takenoko-mebaru, Ukeguchi-mebaru, Ezo-mebaru, Usu-mebaru, Kitsune-mebaru and Tanuki-mebaru. Previously Kōrai-kitsune-mebaru was also known, this is now regarded as the same species as Kitsune-mebaru (Muto et al., 2018). In addition, a single species previously known as simply Mebaru before is now split into three species, Aka-mebaru, Shiro-mebaru and Kuro-mebaru.
Fish named Menuke are also included in the genus Sebastes. Menuke is a generic name for fish in the genus Sebastes having a reddish body and reaching 40–60 cm in length. Menuke inhabit deeper waters, from 200–1000 m depth. When they are caught, barometric pressure is lower than water pressure, and the eyes and stomach protrude outwards. Eyes in such a condition are called “menuke” in Japanese. The following seven species are known to under the name of Menuke: Arasuka-menuke, Bara-menuke, Hireguro-menuke, Kuro-menuke, Arasuka-kuro-menuke, Ara-menuke and Naga-menuke (Sankō-menuke is not included here, following Motomura, 2022, while its validity is recognized in studies such as Nakabo and Kai, 2013). Of them, Kuro-menuke has a yellow and blackish body (not red) and differs from Menuke. The body is dark with grayish to blackish spotted pattern in Arasuka-menuke and varies from dark gray to golden yellow (not red) in Naga-menuke, and they also differ from Menuke. In contrast, Ōsaga and Akōdai lack the name of Menuke, but their bodies are reddish and they are kinds of Menuke. Therefore, it is somewhat confusing that there are species having the name of Menuke but differing from genuine Menuke, and there are species lacking the name of Menuke but are actually genuine Menuke.
I also discuss Futoyubi-menuke and Beni-menuke which may cause further confusion. Although both species are members of the family Sebastidae and have the name Menuke, the former belongs to the genus Adelosebastes and the latter to Hozukius. Therefore, they taxonomically differ from Menuke belonging to the genus Sebastes.
Finally, I show the remaining four Japanese species of Sebastes, Hatsume, Yanaginomai, Gaya-modoki and Aka-gaya. Two of them have the name of gaya, generally Gaya indicates Ezo-mebaru. This is also a little difficult to explain.
IMAMURA Hisashi・Faculty of Fisheries Sciences, Hokkaido University・Professor / the Fisheries Science Center, the Hokkaido University Museum・Director
Figure Illustration of Kuro-mebaru (Sebastes ventricosus), showing in Fauna Japonica edited by P. F. B. von Siebold (deposited in Library of Faculty of Fisheries Sciences, Hokkaido University)
References
Amaoka, K. (1984) Scorpaenidae. Pages 309–318, pls. 276–283 in H. Masuda, K. Amaoka, C. Araga, T. Uyeno and T. Yoshino eds. The fishes of the Japanese Archipelago. Tokai Univ Press, Tokyo.
Amaoka, K., Nakaya, K., and Yabe, M. (2020) Pictorial guide of the fishes of Hokkaido. Hokkaido Shimbun Press, Sapporo (in Japanese).
Imamura, H. (2004) Phylogenetic relationships and new classification of the superfamily Scorpaenoidea (Actinopterygii: Perciformes). Spec Divers 9, 1–36.
Kai, Y., and Nakabo, T. (2013) Taxonomic review of the Sebastes pachycephalus complex (Scorpaeniformes: Scorpaenidae). Zootaxa 3635, 541–560.
Love, M. S., Yoklavich, M., Thorsteinson, L., and Bulter, J. (2002) The rockfishes of the Northeast Pacific. University of California Press, Berkeley and Los Angeles.
Muto, N., Kai, Y., and Nakabo, T. (2018) Taxonomic review of the Sebastes vulpes complex (Scorpaenoidei: Sebastidae). Ichthyol. Res. 66, 9-29.
Nakabo, T., and Kai, Y. (2013) Sebastidae. Pages 668–681, 1933–1938 in T. Nakabo ed. Fishes of Japan with pictorial keys to the species, third edition. Tokai Univ Press, Hadano (in Japanese).
Orr, J. W., and Blackburn, J. E. (2004) The dusky rockfishes (Teleostei: Scorpaeniformes) of the North Pacific Ocean: resurrection of Sebastes variabilis (Pallas, 1814) and a redescription of Sebastes ciliates (Tilesius, 1813). Fish Bull 102, 328–348.
Posted on 31 March 2023
Obstetrics and Gynecology of Mebaru～Introduction of Research for Aquaculture of Sebastes fish～
In Japan, rockfish belonged to a genus Sebastes (generaly called Mebaru and Soi, hereafter the collective term for this genus sometime is stated simply to be Mebaru in following contents) is used as ingredients in various Japanese dishes such as simmered dishes and sashimi, while in Korea and China, they are used in hot pot and steamed fish dishes. In general, fish aquaculture is only viable when a stable supply of seedlings is provided. In addition, the longer the growing period until the fish reach the size for shipment, the greater the risk of increased labor and loss of farmed fish due to disease or accident. Therefore, it could be said that research in aquaculture is often focused on the development of technologies related to stable seedling production and improvement of growth (production volume).
While the majority of fish species are oviparous, Sebastes fish are viviparous fish that give birth to live young. The reproductive mode of these fishes, which undergo a series of processes such as mating, internal fertilization, and gestation, leading to the birth of fry, is an extremely interesting subject for basic biological research. On the other hand, this unusual mode of reproduction may make it impossible to apply common egg-laying fish aquaculture techniques. In addition, compared to other species in aquaculture such as salmonids, yellowtail, and tuna, the growth of the Mebaru fish is slower, and improvement of this growth rate is a key to the success of any aquaculture projects. In this paper, we would like to introduce some examples of recent (or ongoing) research on the Sebastes aquaculture conducted by our research group. Please note that many of the following studies were conducted with the cooperation of the Mariculture Fisheries Research Institute of the Hokkaido Research Organization and the Yakumo-cho Kumaishi Deep Sea Water Comprehensive Exchange Facility and Fisheries Experiment and Research Facility. We would like to take this opportunity to thank them.
HIRAMATSU Naoshi・Faculty of Fisheries Sciences, Hokkaido University・Associate Professor
31 March 2023 posted
Seed Production of Rockfish, the genus Sebastes
Generally, the start of fish farming begins with capturing the fish to be farmed from the wild and using them as parent fish (broodstock). The resulting seedlings are grown for shipment, and the broodstock is selected to produce the next generation of cultured seedlings. This cycle of sustainable reproduction that does not rely on natural seedlings is called hatchery-based (or full-time cycle, or complete) aquaculture. Once hatchery-based aquaculture is achieved, the next step is to perform the selective breeding program that increases the efficiency of aquaculture. Now, as for the Sebastes fish, here are some examples of artificial insemination of Kuro-soi (Sebastes schlegelii) and Kitsune-mebaru (S. vulpes) in Hokkaido, Japan. Initially, Kuro-soi seed production relied on natural mating, which resulted in problems such as the release of unfertilized eggs, premature births, and stillbirths (Noda and Nakagawa, 2010), making the securing of fry unstable. Therefore, the establishment of an artificial insemination technique that could reliably produce fry was necessary. Artificial insemination of the viviparous Sebastes fish was first reported in the Takenoko-mebaru (S. oblongus) (Miyauchi et al., 2011). This was the second case reported by our research group on Kuro-soi (Kawasaki et al., 2017), but it was also the first report on a cold-water species of rockfish, and the first to confirm by DNA analysis that the fry were from the male parents used in artificial insemination, thus proving the effectiveness of the process. The report was also the first to prove the validity of the artificial insemination technique (Kawasaki et al., 2017).
Let’s look at the artificial insemination procedure (Figure 1: Kawasaki et al., 2017). In the case of Kuro-soi and Kitsune-mebaru in Hokkaido, artificial insemination is performed during the mating season, from November to December. First, (1) we select mature males from broodstock kept in tanks that are likely to have sperm reserves, and females that are still in the early stages of ovarian development (early to mid vitellogenesis) at that time, but have the potential to mature and ovulate by spring and be fertilized inside the body. How are they selected? This question will be discussed later. Next, (2) the male is dissected and the seminal reservoir (a tubular organ that stores sperm) is removed. Sperm of the Sebastes fish are highly viscous, so we shred the seminal vesicles in dilutent to extract and dilute the sperm. In the case of the aforementioned Takenoko-mebaru, male urine was used as the diluent, but recently it has been found that easily available fetal bovine serum (FBS) can be used as a substitute. Thirds, (3) the diluted semen is injected into the female's reproductive pore. The injected females are returned to the tank for rearing. In the spring, about six months later, thousands to tens of thousands of fry are born per parent at a rate of 50~60%. Considering that when we relied on natural mating, we had to keep several hundred parent fish in a single tank in order to secure pregnant fish and promote mating, we can say that this method is much more efficient.
Artificial insemination has been successful, but there are still improvements to be made. For example, regarding step (1) above, in some species of Sebastes fish (e.g., Kitsune-mebaru), it is difficult to distinguish by appearance alone when selecting males that are mature at the time of artificial insemination. It is similarly also impossible in all species of Mebaru to select females that are in the early to mid vitellogenic stages of yolk formation at the same time by appearance. In such cases, it is sometimes possible to sort by measuring biomarkers in a blood test. For example, blood sex steroid hormones are candidate markers associated with gonadal development. However, such measurement is relatively complicated and expensive, requiring extraction procedures, etc., making their implementation in aquaculture sites a potential hurdle. An egg yolk protein precursor, vitellogenin (Vtg), is a female-specific serum protein known as another biomarker of female egg development. Our research group has developed a technique to detect and measure this Vtg and has established a technical basis for identifying females with high potential to produce live young (Fig. 2).
On the other hand, there have been no reports on biomarkers for candidate male parent selection other than sex steroids. If a female or immature male is selected by mistake, the abdomen must be opened to obtain sperm, resulting in the wasteful killing of valuable parental fish. Recently, our research group revealed the presence of a large amount of proteins in the urine of mating season males of Sebastes spp. and identified one of them as lipocalin-type prostaglandin D2 synthetase (l-PGDS) (Yamaguchi et al., 2023). As a result, there is a great deal of interest in basic biology regarding the biological function of male urinary proteins in Sebastes fish. It is very interesting from a basic biological point of view, and we are currently conducting research into it, but this will be discussed at a later time. As part of the research on l-PGDS, it was revealed that lipocalin-like protein (LLP), a protein component that reacts with an 1-PGDS antibody, is present in blood (Yamaguchi et al., unpublished). In this study, we examined LLP blood levels in Kuro-soi and Ezo-mebaru (S. taczanowskii) and found that the protein increased with the development of male gonads. Therefore, we believe that LLP is an effective biomarker for selecting male parental candidates with well-developed testes and can be used for artificial insemination in the future.
HIRAMATSU Naoshi・Faculty of Fisheries Sciences, Hokkaido University・Associate Professor
KAWASAKI Takuma・Chief Researcher・Mariculture Fisheries Research Institute (PhD, Hokkaido University)
References
Noda, T. and Nakagawa, M. (2010) Cultivation fishing technology of rockfish Sebastes schlegeli. Cultivation Fishery Technology Series 15, 1-59. (In Japanese).
Miyauchi, M., Uehara, T., Chika, Y., and Mizuguchi, H. (2011) Seeding production of oblong rockfish. Kagawa Prefecture Fisheries Promotion Foundation Business Report 2011, 7-15. (In Japanese).
31 March 2023 posted
Improving Production Efficiency of Sebastes fish
Let's change the topic to research on improving the productivity of Sebastes fish. As mentioned at the beginning of this article, Sebastes fish is relatively slow-growing fish species that take a long time to reach the size required to be shipped (Nakagawa, 2007). The growth of cultured fish depends on the amount of food fed, as well as the rearing environment (water temperature, photoperiod, stocking density, water replacement, amount of dissolved oxygen, etc.), and is also affected by sex, sexual maturity, and genetic factors. To improve the efficiency of aquaculture, it is necessary to optimize these factors related to growth, taking into account the costs of utilities, feed, and other factors, and to shorten the growth period until shipping by as much as possible. In this content, we will discuss the optimization of feeding amounts and the breeding environment on another occasion, and introduce examples of recent research conducted by our group on improving productivity through sex control and breeding.
Kuro-soi grows and matures relatively quickly, making it one of the most frequently cultured species in Japan. In previous studies, it is known that females grow larger than males in Kuro-soi (Nakagawa, 2007). In general, growth of fish species stagnates after maturity. In Kuro-soi, male maturation begins at two to three years of age, whereas female maturation is delayed by several years, so we can expect to see differences in body size between the sexes as they advance in age. In fact, our research group has conducted rearing tests and found that the average weight of males did not exceed 500 g, the expected size for shipment, at 2 years of age, while the average weight of females exceeded 500 g. If only females could be produced (all-female production), production would increase by more than 20% compared to mixed production of males and females (assuming a sex ratio of 1:1). In addition, most females reach 500 g or more at 2 years of age and are ready for shipment, thus significantly shortening the rearing timescale.
In the first step, we are planning to produce a female individual that has been sexually changed to a male (called a "pseudo male"), and in the second step, we will cross this pseudo male with a normal female to produce an all-female population. The sex-determination pattern of Kuro-soi is heterozygous male: XX (genetic female) - XY (genetic male), and having a Y chromosome makes one a male. Sperm are extracted from this pseudo male and artificially inseminated into a normal female (XX) that has not been treated with hormones, resulting in all-female seedlings. At this time, we have attempted the first stage of pseudo male production, and have found that 100% of the individuals determined to be genetically female (XX) by genetic sex identification using DNA analysis have male gonads when treated with male sex hormones. In the future, we believe that the next second step can be accomplished by raising these pseudo males and using their sperm for artificial insemination. The offspring obtained from the cross between the pseudo male parent and the normal female parent will be female because they are all XX, but their genes and the endogenous hormone dynamics in their blood are expected to be no different from those of normal XX females. In fact, efficient production of farmed salmon is widely practiced using all-female seedlings produced by such technology.
Currently, a variety of Sebastes fish are sold at the market in Hakodate, where the Faculty of Fisheries is located. Among them, Kitsune-mebaru (often called Mazoi in the Hakodate vicinity) is known as a high-end fish. Known for its high fat content and good taste, it is a popular fish for sashimi and sushi dishes. On the other hand, Kuro-soi is also popular as sashimi and sushi material, but it is a familiar fish to Hokkaido-area residents who can enjoy it at a more common, affordable price when it is in season, as it has relatively low fat content and a refreshing taste, and many large individuals are caught at certain times of the year. Here, when considered as a farmed fish, the Kitsune-mebaru is a very slow-growing fish compared to Kuro-soi. Breeding is necessary to improve growth while retaining the good flesh quality of the Kitsune-mebaru, but normal breeding takes a very long time, effort, and cost. One of the breeding methods to quickly obtain good traits such as high growth is crossbreeding of different Sebastes fish using hybridization techniques.
Sebastes fish is viviparous fish, and until now, seedling production has relied on natural mating. Therefore, it has been impossible to selectively breed and pass on individuals with specific superior traits, but the establishment of the artificial insemination technique described above has made this possible. Currently, our research group has succeeded in the complete cultivation of Kuro-soi by producing seedlings (F1) from wild-caught parent fish and selecting and breeding high-growth individuals from among the farmed fish raised from the F1 to obtain seedlings (F2). By repeating the process of breeding, selecting, and crossbreeding these F2s over several generations, it is possible to produce a strain with high growth rates and other traits suitable for aquaculture. However, it takes 2-3 years for males and 3-5 years for females to pass from one generation to the next, making repeated passages a lengthy and time-consuming process. Therefore, the laboratory used artificial insemination to create a hybridized strain of Kitsune-mebaru and Kuro-soi (see Welcome photo: Hybrid between Kitsune-mebaru (Mazoi)♀ and Kuro-soi♂).
The growth of these hybrids was compared and found to have intermediate traits of both parents. For example, in growth, the hybrids were larger in body size (66% more female and 26% more male by weight) compared to the strait strain of Kitsune-mebaru. In a blind taste test, both strait parent strain tended to be evaluated differently by different people, but the hybrids were generally highly rated, and we think they can be evaluated as having a taste that can be enjoyed by everyone. Thus, it can be said that the creation of new varieties through hybridization is a breeding method that is easier and more effective in improving traits in a greatly reduced time period compared to conventional breeding. On the other hand, it is worrisome to easily cultivate hybrids in rafts in the sea, considering the possibility that they escape. Recently, advances in land-based recirculating aquaculture technology are making it possible to farm fish in an environment where there is no risk of straying into open sea and interacting with wild fish. With further advances in such technology, the day may come when commercialization of hybrid aquaculture will become a reality.
The above are some examples of research mainly related to the aquaculture using the Sebastes fish as an example. Fish aquaculture provides many opportunities to use techniques similar to those used in the departments of obstetrics and gynecology in humans and animal husbandry in veterinary medicine. These include, for example, fertility treatment, sex determination, sex control, artificial insemination, paternity testing etc. Sebastes are viviparous fish, and although they do not nurse or raise their young after birth, they are similar to humans and other mammals in that they give birth to children gestated in their bodies. Our research may be easier to visualize if we call it Mebaru's obstetrics and gynecology.
HIRAMATSU Naoshi・Faculty of Fisheries Sciences, Hokkaido University・Associate Professor
References
Nakagawa, M. (2007) Effect of rearing temperature on growth and maturation of black rockfish Sebastes schlegeli, Aquacult. Sci. 55, 83-89.
31 March 2023 posted
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