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As the Japanese Kanji name suggests, sculpin (鰍written in Japanese Kanji) is in season in the autumn. It is only spring now, but we can start to learn more about them and get ready to enjoy the taste in autumn. In Hakodate Bay in the autumn, especially at night, it is possible to catch a lot of sculpins. It was late summer when I moved from Sapporo to Hakodate to the Faculty of Fisheries, Hokkaido University. As I was getting used to life in Hakodate, I went to the harbor to do some fishing and experienced an unexpectedly high catch of sculpins. Since it was in season, the taste was good.
Because of the value of sculpin shad as a fishery resource, the Faculty of Fisheries Sciences, Hokkaido University, has professional systematists for the classification of Scorpaeniformes, including sculpin. In addition, there are researchers who are exploring the sculpin from both genetic and ecological viewpoints because of its unexpectedly high species diversity and unexpected reproductive patterns.
So, Professor Imamura and Professor Munehara, who are well known academics, have teamed up to prepare these contents on Sculpin.
When we read it, we will find that sculpin is fascinating!
The two illustrations on the back and side/top in the next section are new species of sculpin described by the Fish Systematics Laboratory, in Faculty of Fisheries Sciences, Hokkaido University (Radulinopsis taranetzi Yabe & Maruyama and Porocottus coronatus Yabe, respectively). The excellent drawing is by Dr. YABE Mamoru, Professor Emeritus of Hokkaido University.
Please read the contents of this sculpin section to improve your knowledge of biology, ecology, physiology, and, of course, fisheries sciences in preparation for the autumn season of sculpin.
FoM Editorial
20 May 2022 posted
Sculpins
Sculpins are fishes classified into the suborder Cottoidei and superfamily Cottoidea. About 400 species in 100 genera are known around the world and more than 130 species are found in Japan. Many species are distributed in cold waters in the Northern Hemisphere, and several species are present in parts of the Southern Hemisphere such as South America, Australia and New Zealand. They inhabit mainly shallow waters in coastal regions on continental shelves, but also in deep sea waters up to 2800 m depth and in fresh waters in such as rivers and lakes. Sculpins are characterized as having features such as a large and compressed head, two dorsal fins, a broad base of the pectoral fin and absence of the swimbladder.
Sculpins are found in Hokkaido and more than 90 species are known from the area. We know species such as Elegant sculpin (Bero elegans) which can be fished from breakwaters and Tentacled sculpin (Porocottus allisi) which can be found in tidepools. We also use species such as Sea raven (Hemitripterus villosus) and Frog sculpin (Myoxocephalus stelleri) as cooking ingredients. Therefore, it can be considered that people living in Hokkaido are familiar with sculpins. However, there are many unknown aspects of sculpins and they can be good research material for researchers in Hokkaido University. For example, among sculpins known from Hokkaido, 9 species were newly described by researchers in this university. We hope you could satisfy your intellectual curiosity on sculpins through FoM.
IMAMURA Hisashi・Faculty of Fisheries Sciences, Hokkaido University・Professor／the Fisheries Science Center, the Hokkaido University Museum・Director
30 May 2022 posted
Species Diversity of Sculpins
Classification of organisms is variable between researchers having different concepts and standpoints. In this section, species diversity of Japanese sculpins is presented based on explanation on characteristics of each of six families recognized in sculpins, following cottoid classification shown in “Fishes of Japan with pictorial keys to the species, third edition” (Nakabo and Kai, 2013) including all known Japanese fish species at that time.
Ereuniidae (deepwater sculpins): Two genera and three species of Ereuniidae (Marukawichthys ambulator, Marukawichthys pacificus and Ereunias grallator) are known around the world. Of these, M. ambulator and E. grallator are known from Japan, and M. pacificus from the Emperor Sea Mounts. They are characterized as having features such as free pectoral fin rays on the lower portion of the fin.
Rhamphocottidae (grunt sculpins): The family Rhamphocottidae consists of only a single species, Rhamphocottus richardsonii. This species has a mouth like a beak of bird, a large head comprising more than half of the body, a higher body and free pectoral fin rays on the lower portion of the fin. It is distributed from Iwate Prefecture to the Sagami Bay in Japan, and also from the eastern coasts of Kamchatka, Bering Sea and western Alaska Bay to Santa Monica Bay in California.
Hemitripteridae (sea ravens): The family presently includes three genera and eight species from the northern Pacific and northern West Atlantic, and four species in the three genera (Hemitripterus villosus, Nautichthys pribilovius, Blepsias cirrhosis and Blepsias bilobus) from Japan. The species in this family commonly have minute spines covering the body.
Cottidae (sculpins): The family Cottidae is a group having the richest species diversity in Cottoidea, including about 70 genera and 300 species around the world, with 32 genera and 87 species in Japan. Cottids are mainly distributed in cold water regions in the Northern Hemisphere, but also in eastern Australia, New Guinea and New Zealand. Many cottids inhabit sea waters, but species such as members of Cottus occur in fresh water. They are mainly found in shallow coastal regions, but Antipodocottus elegans is known to occur at a depth of 735 m. Cottids share characteristics such as a naked body or sparsely covered with scales or modified scales.
Psychrolutidae (tadpole sculpins): About 30 species in seven genera of tadpole sculpins are known from the Pacific, Indian and Atlantic oceans, and 11 species in six genera are found in Japan. They inhabit shallow coastal regions (species such as Psychrolutes sigalutes) to 2800 m depth in Psychrolutes phrictus. This family is characterized as having soft naked bodies, sometimes covered with small prickles, spinous and soft ray parts of the dorsal fin continuous and partly hidden under skin, and a reduced lateral line.
Agonidae (poachers): The family Agonidae includes 12 genera and 44 species known from the Artic, northern Atlantic, northwest Pacific and southern South America, and 13 genera and 23 species found in Japan. Agonid species inhabit shallow coastal regions to deep water regions over 1000 m. They are characterized as having the body covered with bony plates and are usually slender, with all fin rays unbranched.
IMAMURA Hisashi・Faculty of Fisheries Sciences, Hokkaido University・Professor／the Fisheries Science Center, the Hokkaido University Museum・Director
References
Nakabo T., Kai Y. (2013) Cottoidei. Pages 1152–1218, 2059–2076 in Nakabo T ed. Fishes of Japan with pictorial keys to the species, third ed. Tokai University, Hadano (in Japanese).
Nelson J. S., Grande T. C., Wilson M. V. H. (2016) Fishes of the world, fifth edition. Wiley, New Jersey.
Yabe M. (2011) Chapter 1. Species diversity and morphological evolution in sculpins. Pages 2–42 in Munehara H, Goto A, Yabe M eds. Diversity of cottoid fishes. Adaptation and evolution. Tokai University, Hadano (in Japanese).
30 May 2022 posted
Groups with Close Relationship to Sculpins
The superfamily Cottoidea is classified into a higher taxonomic group, the scorpaeniform suborder Cottoidei. This suborder is characterized as having the parietal supporting a sensory canal, six branchiostegal rays and swimbladder muscle derived from a body muscle of the epaxialis. Cottoidei also includes five superfamilies other than Cottoidea. They are described below, following a classification shown by Nelson et al. (2016).
Cyclopteroidea (lumpfishes and snailfishes): The superfamily Cyclopteroidea is a group most closely related to the superfamily Cottoidea, and includes the families Cyclopteridae (lumpfishes) and Liparidae (snailfishes). Species belonging to the two families usually have a disk formed by the continuous pelvic fins on both sides, but some liparids have a reduced disk or lack it entirely. Cycloplerids are mainly distributed in cold waters in the Northern Hemisphere, but some species, such as Lethotrenus awae distributed in the Yellow Sea and off Japan Sea in western Japan, are also known. Cyclopetridae includes 27 species around the world and 11 species in Japan. Nelson et al. (2016) recognized about six genera in the family, while Oku et al. (2017) included four genera based on phylogenetic relationships. Lumpfishes have a globose body, usually covered with tubercules. Liparidae includes about 400 species in 10 genera distributed from the Arctic to the Antarctic. Of these, about 10 genera and 50 species are found in Japan. Snailfihes have jellylike skin and scaleless body (or covered with small prickles in some species).
Trichodontoidea (sandfishes): The superfamily Trichodontoidea, including only the family Trichodontidae, is considered to be closely related to a group formed by Cottoidea and Cyclopteroidea. Sandfishes had previously been included in the perciform suborder Trachinoidei, while it was recently recognized that Trichodontidae has a close relationship with sculpins in molecular and morphological studies [e.g., Smith and Wheeler, 2004 (molecular study); Imamura et al., 2005 (morphological study)]. Trichodontidae includes only two genera and two species (Arctoscopus japonicus and Trichodon trichodon). Both species are known from the northern Pacific and only A. japonicus is distributed in Japan. The family is characterized as having features such as a compressed body lacking scales, the near vertical mouth with fringed lips and a preopercle with five sharp spines.
Hexagrammoidea (greenlings): Hexagrammoidea contains only the family Hexagrammidae. This family includes three genera and nine species known from the North Pacific, and two genera and seven species are found in Japan. Hexagrammids have characteristics such as a head without ridges and spines, and one dorsal fin. Ophiodon elongatus (lingcod) reaches 1.5 m in length.
Zaniolepidoidea (combfishes): Only the family Zaniolepididae is included in Zaniolepidoidea. This family consists of two genera and three species distributed in the eastern Pacific from British Colombia to California. Zaniolepididae has characters such as the anal fin anteriorly with three spines (four spines are also recognized in Oxylebius pictus).
Anoplopomatoidea (sablefishes): Anoplopomatoidea contains only the family Anoplopomatidae. This family includes two genera and two species, Anoplopoma finbria and Erilepis zonifer, both known from the northern Pacific, including Japan. Anoplopomatidae has a head without spines and ridges, and two dorsal fins. Both species in the family are large, reaching 1 m in A. finbria and 1.8 m in E. zonifer. Some researchers recognize that sablefishes were initially branched off from the suborder Cottoidei and others consider that they lack a close relationship with the suborder.
IMAMURA Hisashi・Faculty of Fisheries Sciences, Hokkaido University・Professor／the Fisheries Science Center, the Hokkaido University Museum・Director
References
Nakabo T., Kai Y. (2013) Cottoidei. Pages 1152–1218, 2059–2076 in Nakabo T ed. Fishes of Japan with pictorial keys to the species, third ed. Tokai University, Hadano (in Japanese).
Nelson J. S., Grande T. C., Wilson M. V. H. (2016) Fishes of the world, fifth edition. Wiley, New Jersey.
Smith W. L., Wheeler W. C. (2004) Polyphyly of the mail-cheeked fishes (Teleostei: Scorpaeniformes): evidence from mitochondrial and nuclear sequence data. Mol. Phylogenet. Evol. 11, 441–458.
Yabe M. (2011) Chapter 1. Species diversity and morphological evolution in sculpins. Pages 2–42 in Munehara H, Goto A, Yabe M eds. Diversity of cottoid fishes. Adaptation and evolution. Tokai University, Hadano (in Japanese).
30 May 2022 posted
Phylogenetic Relationships and Classification of Sculpins
Phylogenetic relationships of sculpins have been assumed by many researchers. The oldest research was performed by Gill (1888). Gill (1888) inferred phylogenetic relationships of the order Scorpaeniformes, a larger taxonomic group including the suborder Cottoidei, based on fragmental osteological information and showed that the families Cottidae and Hemitripteridae are closely related to each other, and the families Rhamphocottidae and Agonidae are related to scorpaenoid Triglidae and Peristediidae. Based on osteological and other characteristics, Matsubara (1955) regarded Cottidae and Agonidae as showing a close relationship, and these families are further related to a group including Cyclopteridae and Liparidae. Yabe (1985) examined osteology and myology in detail, assumed comprehensive phylogenetic relationships of the superfamily Cottoidea and recognized the following six families based on the relationships: Ereuniidae, Rhamphocottidae, Hemitripteridae, Cottidae, Psychrolutidae and Agonidae. At the time of Yabe studies, it was difficult for foreign researchers to examine Russian specimens and he was not able to include Abyssocottidae and Comephoridae known from Lake Baikal in his phylogenetic analyses, and Yabe (1985) tentatively recognized these families as belonging to the superfamily Cottoidea. In addition, although he also did not include Normanichthys crockeri, a sole member of the family Normanichthyidae, in his phylogenetic analysis, he placed the family in Cottoidea. However, Normanichthyidae was regarded as not belonging to Cottoidea by subsequent morphological studies (Yabe and Uyeno, 1996; Imamura and Yabe, 2002). After Yabe (1985), the family Bathylutichthyidae was established in 1990, but some researchers do not recognize the family, as mentioned below.
In addition to morphological characters, recently molecular data has also been used for phylogenetic analyses. For example, Smith and Wheeler (2004) assumed phylogenetic relationships of the order Scorpaeniformes based on mitochondrial and nuclear DNA sequence data and showed phylogenetic hypotheses such as a close relationship between Rhamphocottus and Marukawhichthys, but they did not propose any classification based on it. Smith and Busby (2014) analyzed 4518 molecular and 72 morphological characters for 69 species, and showed the following phylogenetic hypotheses on Cottoidea: 1) cottid Jordania forms a distinct clade including only one genus; 2) rhamphocottid Rhamphocottus and ereuniid Marukawhichthys have a sister relationship and form a distinct clade including these genera; 3) cottid Scorpaenichthys forms a distinct clade including only one genus; 4) cottid Hemilepidotus, Hemitripteridae and Agonidae are closely related, and form a distinct clade including the three groups; 5) cottid Leptocottus known from marine waters, freshwater cottid genera such as Cottus and Cephalocottus, and Abyssocottidae and Comephoridae known from the Lake Baikal are closely related, and form a distinct clade; and 6) cottid genara living in marine waters such as Enophrys, Myoxocephalus and Icelus, and Psychrolutidae are closely related, and form a distinct clade. Based on these hypotheses, Smith and Busby (2014) recognized six families, Jordaniidae, Rhamphocottidae, Scorpaenichthyidae, Agonidae, Cottidae and Psychrolutidae, in the above-mentioned six clades, respectively. Following Smith and Busby (2014), these six families are summarized below.
Jordaniidae: Includes two species belonging to Jordania and Paricelinus, which were formerly classified in Cottidae. This family is defined by one characteristic, presence of the first pharyngobranchial.
Rhamphocottidae: Includes three genera and four species, which were formerly classified in Rhamphocottidae and Ereuniidae. It is defined by four characteristics including having free pectoral fin rays on the lower portion of the fin.
Scorpaenichthyidae: Includes one species belonging to Scorpaenichthys, having formerly been classified into Cottidae. This family is defined by two characteristics including having no body scales.
Agonidae: Includes 26 genera and about 60 species, which were formerly classified in Agonidae and Hemitripteridae, and Hemilepidotus , formerly Cottidae. Agonidae is defined by one characteristic, scales modified into dermal spines in larvae or pelagic juveniles.
Cottidae: Includes 18 genera and about 107 species of freshwater sculpins formerly included in Cottidae, Abyssocottidae and Comephoridae, and marine genus Leptocottus formerly in Cottidae. This family is defined by four charactersistics, including the gill membrane fused with the isthmus.
Psychrolutidae: Includes 64 genera and about 214 species formerly included in Psychrolutidae, Bathylutichthyidae and marine cottid genera other than the above-mentioned genera. Psychrolutidae is defined by two charactersistics including having three or fewer pelvic fin rays.
Of the six families, Jordaniidae and Scorpaenichthyidae had not been recognized recently until Smith and Busby (2014), and definitions and limits of other four families are quite different from those previously recognized. This might be a reason for Nelson et al. (2016), recognizing four families other than Cottidae and Psychrolutidae defined by Smith and Busby (2014), but using the former Psychrolutidae with previous definition and recognized Bathylutichthyidae. In addition, they recognized Cottidae as a group formerly included in Cottidae, Abyssocottidae and Comephoridae, and provided subfamilial rank with each of three former families, partly following Smith and Busby (2014) and partly following previous classifications.
As showed above, classification is variable when a new hypothesis on phylogenetic relationships is proposed, and researchers may accept different classifications.
IMAMURA Hisashi・Faculty of Fisheries Sciences, Hokkaido University・Professor／the Fisheries Science Center, the Hokkaido University Museum・Director
References
Gill T. (1888) On the classification of the mail-cheeked fishes. Proc. US Nat. Mus. 11, 567–592.
Matsubara K. (1955) Fish morphology and hierarchy. Ishizaki Shoten, Tokyo (in Japanese).
Nakabo T., Kai Y. (2013) Cottoidei. Pages 1152–1218, 2059–2076 in Nakabo T ed. Fishes of Japan with pictorial keys to the species, third ed. Tokai University, Hadano.
Nelson J. S., Grande T. C., Wilson M. V. H. (2016) Fishes of the world, fifth edition. Wiley, New Jersey.
Smith W. L., Busby M. S. (2014) Phylogeny and taxonomy of sculpins, sandfishes, and snailfishes (Perciformes: Cottoidei) with comments on the phylogenetic significance of their early-life-history specializations. Mol. Phylogenet. Evol. 79, 332–352.
Smith W. L., Wheeler W. C. (2004) Polyphyly of the mail-cheeked fishes (Teleostei: Scorpaeniformes): evidence from mitochondrial and nuclear sequence data. Mol. Phylogenet. Evol. 11, 441–458.
Yabe M. (1985) Comparative osteology and myology of the superfamily Cottoidea (Pisces: Scorpaeniformes), and its phylogenetic classification. Mem. Fac. Fish Hokkaido Univ. 32, 1–130.
Yabe M. (2011) Chapter 1. Species diversity and morphological evolution in sculpins. Pages 2–42 in Munehara H, Goto A, Yabe M eds. Diversity of cottoid fishes. Adaptation and evolution. Tokai University, Hadano (in Japanese).
Yabe M., Uyeno T. (1990) Anatomical description of Normanichthys crockeri (Scorpaeniformes, insertae sedis: family Normanichthyiudae). Bull. Mar. Sci. 58, 494–510.
30 May 2022 posted
Which Fish Have the Most Species Diversity in Hokkaido?
Thirty-one years have passed since the United Nations Conference on Environment and Development, the so-called Earth Summit, and the term “biodiversity” has become one of the most commonly used terms in everyday life. The usage varies depending on the natural environment, region, population, and other points of interest, depending on whether the level of diversity is an ecosystem, a biological community, or a genetic variation within a species, but “species” is the basic unit of an organism. So, do you know which fish have the most species diverse in Hokkaido? The answer means the representing fish in Hokkaido. Let's find out.
Biota found within a geographically separated area, such as a country, area of sea or an island, are collectively called the "Fauna or flora" of the place. If it is limited to the fish that inhabit Japan, it is called "Japanese fish fauna", and if it is narrowed down to Hokkaido, it is called "Hokkaido fish fauna". So far, there have been about 800 species of fish recorded in Hokkaido (Amaoka et al., 2020). Since there are about 4200 species in 359 families in Japan (Nakabo, 2013), 20% of the species are found in Hokkaido. We have created the top ten species ranking for Hokkaido and Japan by grouping these species by "family" (Table 1). The meaning of this ranking is the ranking of fish that are prospering in each range in Hokkaido and Japan.
The first place in the ranking of Hokkaido is Cottidae. That means that the most prosperous fish in Hokkaido is Cottidae. Cottidae have 88 species in the Japanese ranking and is ranked 6th out of 359 families. 60 species, which is 70% of them, are sculpins that live in Hokkaido. Cottidae are fish that symbolize Hokkaido. The web page on which this article is posted introduces research being conducted at Faculty of Fisheries Sciences, Hokkaido University. This is also the reason why sculpin appeared next to salmon and kelp, which are synonymous with the fishery industry in Hokkaido.
At the United Nations General Assembly held in New York in 2015, the Sustainable Development Goals (SDGs) were agreed internationally in 150 countries and regions. One of the 17 SDGs has the theme of "Protecting the abundance of the sea." What should I learn to preserve the environment of the sea and rivers in Hokkaido? Understanding the sculpin well is the first step.
MUEHARA Hiroyuki・Field Science Center for Northern Biosphere, Hokkaido University, Usujiri Fisheries Station
References
Amaoka K., Nakaya K., Yabe M. (2020) Pictorial Guide to the Fishes of Hokkaido. Hokkaido Shinbunsha.
Nakabo T. (2013) Fishes of Japan with pictorial keys to the species the 3rd ed. Tokai University Press.
30 May 2022 posted
Why Could the Cottoidei Diverge So Many Species in the North Pacific? The Secret-1: Internal Gametic Association Type
From Hokkaido to the Kuril Islands, Kamchatka Peninsula, Aleutian Islands, Alaska Peninsula, Vancouver Island, Canada, and the coast of California, the Pacific Rim coastal area is a cold sea area where the water temperature rarely exceeds 20 ° C even in summer. We often see fish belonging to the suborder Zoarcoidei and Cyclopteridae, with the sculpins at the top. It is a big presence in terms of species diversity. The three groups have some common characters. There are many species that have poor swimming ability and have an ecology that hides on the seabed, eggs are well protected until hatching so that they are not predated, and there are many species that mate with the Cottoidei and the Zoarcoidei (Munehara 2011).
In this general breeding style of fish, which lay eggs and release sperm in water, fertilization is not possible unless males and females physically interact when the females lay eggs. There are costs and risks associated this behavior, such as the time spent to find a partner and the risk of predation during mating. In contrast, if fish can mate and then store sperm in its selve ovaries, the fish can reduce that risk.
Fertilization is the process of combining one set of genomes of an egg cell and one set of sperm into two sets in one cell. Before fertilization, sperm have completed meiosis, but the egg cell stops in the middle of meiosis and waits for sperm to be introduced. There is also a limit to stopping division (within hours to days depending on the species), and eggs that are too old (overripe) lose fertility. Egg cells can be fertilized only after the follicular cells that surround the outside of the fetal membrane have ruptured and ovulated. So if the sperm are waiting for ovulation in the ovaries, you can reduce the risk of overripening. In mating sculpins, sperm and eggs combine in such a way (Fig. 1).
The sperm of the mating sculpin invades a narrow passage called the micropyle, and following by reaches the sperm receptor at the entrance of the egg cell (Munehara et al. 1989). The sperm will be ‘on standby’ at a position where fertilization can be performed at any time. Fertilization begins after the egg is laid in the sea. In the case of sculpins, the environment inside the ovary lacks the certain conditions to initiate fertilization (Munehara et al. 1994). This type of fertilization is called "internal gametic association". This mode of fertilization, which is not internal fertilization, has another important significance.
Fertilized egg cells become "embryos" and require oxygen as they develop. With internal fertilization, there is a limit to how long a female can find a spawning site, after which embryos will suffocate or fail to develop normally even not dying. In "internal gamete association", although the limitation of the risk of eggs becoming overripe, females have more time to find a suitable place for spawning. Reproductive modes of sculpins include female care for eggs and laying eggs in invertebrates such as sea pineapples and sponges. The breeding styles are realized by evolution of copulation (Abe and Munehara 2009).
MUNEHARA Hiroyuki・Field Science Center for Northern Biosphere, Hokkaido University, Usujiri Fisheries Station
References
Abe T., Munehara H. (2009) Adaptation and Evolution of Reproductive mode in Copulating Cottoid Species. pp221-246, In “Reproductive Biology and Phylogeny in Fishes” edited by B.G.M. Jamieson, Science Publisher, Enfield, USA.
Munehara H. (2011) Evolutionary process of adaptive diversity of the cottoid fishes discussed from ecological aspects. pp85-120, In “Diversity of Cottoid Fishes –adaptation and evolution-”. Tokai University Publisher.
30 May 2022 posted
Why Could the Cottoidei Diverge So Many Species in the North Pacific? The Secret-2: Plankton Life, Juvenile Period and Lack of Bladder
The ecology that is the exact opposite of benthic will be the migratory life of herring, salmon, etc. These fish are widely distributed, are an important fishery resource, and are widely consumed. However, the species diversity is not so large. For example, herring inhabiting any parts of northern Japan is a single species, Clupea pallasii. Herring imported from Canada and Alaska is also the same species (note herring from the Atlantic Ocean are the different species). The salmon found in rivers in Hokkaido and the salmon that in the Kamchatka Peninsula, Alaska, and Canada are the same species Oncorhrynchus keta. Populations inhabiting different rivers, never breed one another, but are not so different that they can be divided into different species. On the other hand, the three families (Cottoidei, Zoarcoidei, Cyclopteridae) are prosperous in the Pacific Rim, but each species are not as widely distributed as migratory fish. There are many cases where species with similar morphology are distributed sympatrically or adjacently. For example, six species in each of the genus Gymnocanthus and the genus Hemilepidotus, inhibit each specific limited distribution areas in the east and west of the North Pacific Ocean, the Bering Sea and the Arctic Ocean. There seems to be a negative correlation between "species diversity" and "distribution area". This is an important research theme in ichthyology that leads to phylogeny and evolution. Let’s examine about sculpins.
Sculpin hatch as small larvae and must begin immediately independent life. Although it is benthic, it initially leads a ‘floating’ life like that of plankton. During this period, it is possible to move and expand its distribution either by riding ocean currents or swimming on its own. However, in a study of Canadian sculpins breeding in shallow water, the larvae stay within a range of 20 m from the shore throughout plankton stage and changes to the benthic stage in about a month (Marlieve 1986). This early life history, which has a short plankton life and is rarely offshore, is found in many sculpin species. One of the reasons is that they don’t have the swim bladder. Also, as showed by the large head, they have a thick body shape. Early larvae have long trunk, and have a slender form suitable for swimming, but as they grow closer to their adult form, their bodies become heavier and at last they are forced to switch to benthic life.
The first step in ecological studies concerning any fish is to identify the species, but there is often difficulties in studying larval stages. When sculpin reach the adult stage, each species has the specific appearance, but during the planktonic stages, the difference between different species is small and it is difficult to distinguish them. In such cases, it is possible to identify the species by examining the gene (DNA barcoding), but without the genetic information of the specimen that has been correctly identified, it is not possible to make a correct identification (Momota and Munehara 2017; Azuma and Munehara 2021). The morphological specimens and genetic information of all sculpin fry is essential, but the number registered in the database is still less than half the complete total. Research on sculpin fry is currently under development.
MUNEHARA Hiroyuki・Field Science Center for Northern Biosphere, Hokkaido University, Usujiri Fisheries Station
References
Marlieve J. B. (1986) Lack of planktonic dispersal of rocky intertidal fish larvae. Trans. Am. Fish. Soc. 115, 149-154.
30 May 2022 posted
Why Could the Cottoidei Diverge So Many Species in the North Pacific? The Secret-3: Antifreezing Protein
All the fish that thrive in the North Pacific are resistant to low water temperatures. Even so, there are only a few fish species that can live in the Arctic Ocean. Of the 400 species of the Cottoid, only 18 species of the Cottidae, 8 species of the Psychrolutidae , 4 species of the Agonidae, and 2 species of the Hemitripteridae could invade so extreme low temperature condition (Munehara 2020). Creatures that are not prepared to survive in the sub-zero sea will soon perish as the blood and body fluids (intercellular spaces) freeze and eventually all life activities cease. How can fish adapt to such conditions?
Freezing is a phenomenon in which ice crystals appear in water, water molecules bind to them, and the crystals grow and become solid. Therefore, to prevent water freezing, it is necessary to prevent the appearance of ice crystals and to inhibit their growth. There are several ways to do this. For example, preventing ice crystals formed in seawater from entering the body. The method of protecting the body surface with slimy mucus is effective. However, there are some organs such as gills that have to come into direct contact with seawater, so it is not a complete defense. Heating body temperature like tuna is one strategy, but to generate heat in sea water just consumes a large amount of energy, and largely prevents creatures from grow or reproduce.
Fish that can survive in the icy sea have one thing in common. Having a gene that encodes antifreeze protein or antifreeze glycoprotein. These are biopolymer substances that are synthesized in the liver and skin, dissolve in blood and body fluids, and have functions such as "freezing point depression," "protection of cell membranes from outside the cell," and "inhibition of ice crystal development." Of the three functions, the one that exerts the high antifreeze effect is the inhibition of ice crystal development (Fig. 1; De Vries and Wohlschlag 1969; Rubinsky et al. 1990).
Concerning sculpins, biochemical analysis was underway for species inhabiting the Arctic Ocean and the North Atlantic Ocean. At Hokkaido University, Dr. Aya Yamazaki, who was a graduate student at the time when she boarded the training ship Oshoromaru's Arctic voyage in 2013, collected Siberian staghorn sculpin and participated in antifreeze protein research from an evolutionary ecological point of view. As a result, we found that the multiplicity and synthetic ability of antifreeze protein genes are higher in the genus Myoxocephalus, which has advanced to the North Atlantic Ocean, than in the genus Gymnocanthus, which extends to the Arctic Ocean. From the molecular phylogenetic analysis, the invasion time into the Arctic Ocean of the Cottoidei (Myoxocephalus entered into the Arctic Ocean about 7.9 million years ago when the Bering Strait was first opened, and Gymnocanthus envaded at 3 million years ago when the strait reopened after closing) was coincided to the age at which the antifreeze protein synthesis ability was acquired (Yamazaki et al. 2018, 2019). This research has revealed one of the mysteries that sculpins have been able to advance into diverse distribution areas as well as species diversity (Yamazaki and Munehara 2018).
Here, we introduced why marine cottoid fish could diverge so many species in the North Pacific. About 100 species of sculpins are known even in freshwater areas, and they are prospering throughout the northern hemisphere, including Japan, the Eurasian continent, and the North American continent.
MUNEHARA Hiroyuki・Field Science Center for Northern Biosphere, Hokkaido University, Usujiri Fisheries Station
References
Munehara H. (2020) Great journey of the coastal fishes of Hokkaido. Kaibundo.
Yamazaki A., Munehara H. (2018) Low temperature tolerance and Antifreeze Protein in cottoid fishes. pp. 85-95，in “Functions and Applications of Antifreeze Protein” ed. Tsuda S. CMC publisher.
30 May 2022 posted
Donation & Research Collaboration
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