The photophores along the body of the squid can be used against predators in either a warning form or as counter-illumination camouflage. The northern fur seal, Callorhinus ursinus, is a known predator.
Known Predators:
Anti-predator Adaptations: aposematic ; cryptic
Watasenia scintillans is a small cephalopod, growing to 7-8 cm. The firefly squid is equipped with special light producing organs called photophores. Photophores are found in many parts of the body but large ones are usually found on the tips of the tentacles as well as around the eyes. These lights can be flashed in unison or alternated in patterns. This squid has arms with hooks and tentacles with hooks and one series of suckers. The mouth cavity has dark pigmentation.
Average length: 7.62 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
The firefly squid lives for about one year.
Watasenia scintillans is a marine animal found in depths of 200 to 400 meters.
Range depth: 200 to 400 m.
Habitat Regions: temperate ; tropical ; saltwater or marine
The geographic range of Watasenia scintillans is the Western Pacific ocean around Japan.
Biogeographic Regions: pacific ocean (Native )
The photophores along the body and tentacles of the Watasenia scintillans are used to attract prey, provide camouflage, frighten predators, and to attract a mate. The firefly squid also has highly developed vision. Its eyes contain three different types of light-sensitive cells and are believed to be capable of distinguishing different colors.
Communication Channels: visual
Other Communication Modes: photic/bioluminescent
Perception Channels: visual
Watasenia scintillans is not protected under any conservation program.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Fertilized eggs hatch in 6-14 days depending on the water temperature, which varies from six to 16 degrees Celsius. Higher temperatures encourage quicker hatching.
At 15 degrees Celsius, one hour after fertilization, polar bodies appear, followed in five hours with first cleaveage. By 10 hours, 100 or more cells have been formed, and around 16 hours the embryonic lobe has been developed. The embryonic lobe covers about half of the egg in a day and a half. In four days, primordial eyes are present and oral depression starts. A day later, primordial arms, mantle, and funnel appear and then chromatophores appear on the mantle and the eyes are developed. Final organ and chromatophore formation and hatching occurs in 8-8.5 days.
Development - Life Cycle: metamorphosis
Eating raw Watasenia scintillans, known in Japan as Hotaruika, that is infected with spirurina type X larvae, belonging to the phylum Nematoda, can cause abdominal pain, nausea and vomiting, diarrhea, creeping eruption, and ileus (bowel obstruction).
Negative Impacts: injures humans (causes disease in humans )
Watasenia scintillans can be eaten raw, known as Hotaruika in Japan, or cooked. These species of squid also draw large crowds during their spawning season at Toyama Bay in Japan. The large schools that swim up to the shallow waters light up the dark water along the shore, giving tourists a nighttime show. This spectacle has led to the bay being named a Special Natural Monument and construction of a museum devoted to the species.
Positive Impacts: food ; ecotourism
Watasenia scintillans are prey for northern fur seals, Callorhinus ursinus and is a predator of shrimp, fish, and planktonic crustaceans. This squid is also a host to nematode larvae.
Commensal/Parasitic Species:
Watasenia scintillans consumes a diet consisting of shrimp, crabs, fish, and planktonic crustaceans. The photophores on the tips of its tentacles are used in a flashing pattern to attract prey, especially fish.
Animal Foods: fish; aquatic crustaceans; other marine invertebrates; zooplankton
Primary Diet: carnivore (Piscivore , Eats non-insect arthropods)
Bioluminescent photophores can attract mates and be used for communication with other squids.
The spawning season runs from March to May. During this time, firefly squids can be seen gathering in large numbers to lay their eggs. Once the eggs have been released into the water and fertilized, the adult squid die. This completes the one-year life cycle of the squid.
Breeding interval: Once yearly
Breeding season: March - May
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: seasonal breeding ; broadcast (group) spawning; oviparous
Adult firefly squids die after eggs have been released into the water and fertilized.
Parental Investment: no parental involvement
Der Leuchtkalmar (Watasenia scintillans) ist ein Tintenfisch (Coleoidea) und gehört zur Klasse der Kopffüßer (Cephalopoda).
Der Leuchtkalmar ist eine kleine Tintenfischart, die nur etwa 7,5 bis 8 cm groß wird. Sie besitzt, wie für Tintenfische üblich, zehn Arme, von denen zwei verlängert sind und als Tentakel dienen. Acht Arme sind mit gestielten Saugnäpfen besetzt. Die Tentakel sind frei von Saugnäpfen und besitzen 2 bis 3 Haken in einer Reihe. Am Hinterende des Körpers dienen zwei seitliche Flossen der raschen Fortbewegung. Die Tiere besitzen über den Körper verteilt pigmenthaltige Zellen, Chromatophoren, und lichtaussendende Zellen von Photophoren, die lumineszieren (Photophoren jedoch nicht an der Dorsalseite). Die Art kann mit ihren hochentwickelten Linsenaugen Farben unterscheiden.
Der Leuchtkalmar lockt mit den Photophoren kleine Fische an, die er dann mit den Armen umfängt.
Die Art kommt nur auf dem Schelf und den flacheren Gewässern um Japan herum und im Chinesischen Meer bis im Norden zum Ochotskischen Meer vor. Die Tiere leben normalerweise in einer Tiefe von 200 bis 400 m, kommen aber zur Paarung und zur Eiablage in flachere Gewässer und in der Toyama-Bucht des Japanischen Meeres auch verhältnismäßig nahe an die Küsten.
Die Eier werden hauptsächlich in den Monaten Februar bis Juli in den oberen 80 m im freien Wasser abgelegt. In manchen Gegenden erfolgt die Eiablage fast das gesamte Jahr hindurch. Ein Weibchen kann bis zu 20.000 Eier in Strängen bis 1 m Länge ablegen. Das einzelne Ei misst etwa 1,5×1 mm. Die Jungen schlüpfen in Abhängigkeit von der Wassertemperatur nach 6 bis 14 Tagen aus den Eiern (je wärmer das Wasser, desto schneller schlüpfen die Jungen). Der Schlüpfling misst etwa 1,2 bis 1,4 mm. Die durchschnittliche Lebenserwartung der Tiere beträgt nur etwa 1 Jahr.
Leuchtkalmare werden von großen Grundfischen und Verwandten der Lachse gejagt.
Der Leuchtkalmar wird in Gewässern um Japan kommerziell gefischt. Zwischen 1990 und 1999 wurden jedes Jahr etwa zwischen 5000 und 7000 Tonnen gefangen. Die Tiere werden zwischen März und Juni gefischt.
Die Art ist die einzige Art der Gattung Watasenia (Ishikawa, 1914).
Der Leuchtkalmar (Watasenia scintillans) ist ein Tintenfisch (Coleoidea) und gehört zur Klasse der Kopffüßer (Cephalopoda).
The firefly squid (Watasenia scintillans), also commonly known as the sparkling enope squid or hotaru-ika in Japan,[3] is a species of squid in the family Enoploteuthidae.[4] It is the sole species in the monotypic genus Watasenia.[4] These tiny squid are found on the shores of Japan in springtime during spawning season, but spend most of their lives in deeper waters between 200 and 400 metres (700 and 1,300 feet; 100 and 200 fathoms).[5] They are bioluminescent organisms and emit blue light from photophores, which some scientists have hypothesized could be used for communication, camouflage, or attracting food, but it is still unclear in the scientific community exactly how this species uses their bioluminescence.[3] The firefly squid is a predator and actively hunts its food, which includes copepods, small fish, and other squids.[3] The lifespan of a firefly squid is about one year. At the end of their lives, females return close to shore to release their eggs and then die shortly thereafter. This mass migration of firefly squid to the shore is a lucrative business for Japanese fishermen, and during spawning season many go out to the bays to collect the dying squid. Many more also visit Japan during spawning season to see the bright blue light created from the firefly squid's bioluminescence light up the bay, making their spawning season not only a fishing opportunity but also a tourist attraction.[5]
The firefly squid belongs to the Cephalopoda class and the superorder Decapodiformes, commonly known as squid. Their body consists of a distinct head and mantle, and has a bilaterally symmetrical layout. They are soft-bodied organisms with a skeletal structure composed of chitin. They have relatively large eyes, eight arms, and two tentacles. They are further classified into the order Oegopsida for possessing the characteristic traits of having no tentacle pockets in the head and no suckers on the buccal supports. They belong to the family of Enoploteuthidae, based on the hooks on their tentacles.
On average, an adult firefly squid is approximately 7.5 cm (3 in) in length.[3] They are brown/red in color, but emit blue and green light by their photophores. Firefly squid possess three types of photophores.[6] There are multiple (800-1000) small photophores covering the ventral surface of its body, five larger photophores around the lower margins of each eye, and three very large photophores at the tip of each of the fourth pair of ventral legs.[7][6] The photophores that dot the body of the squid produce two different wavelengths of light (both blue and green bioluminescence) while those around the eye and on the legs only produce blue light.[8] The reactant luciferin and the necessary enzyme luciferase are located in a crystalline structure within rod-like bodies in their photophores.[9][10] Firefly squid are the only cephalopods to have this structural arrangement which increases the efficiency of its bioluminescence and allows the light to be directed downward in a cone-like projection.[11] This directed cone of bioluminescence is hypothesized to allow the Firefly squid to better detect its prey and predators from below and attract small fish to eat.[11] The photophores on the tips of its fourth ventral legs produce a very intense light that can be seen by the naked eye.[12]
The firefly squid inhabits the waters off the coast of Japan.[13][14] The depth at which these squids can be found varies (300–400 m or 1,000–1,300 ft during the day, and 20–60 m or 70–200 ft during the night) over the course of a day,[14] as they are one of the several species of squid that participates in diel vertical migration.[14][15] For this reason, they also experience a significant change in environmental temperatures throughout the course of a day(3–6 °C or 37–43 °F during the day and 5–15 °C or 41–59 °F during the night).[14] The firefly squid is especially well known for its yearly migration to the coastal waters of Toyama Bay for the purpose of reproduction.[13][14][15]
The diet of a firefly squid changes throughout its life stages. During its paralarval stage, its diet is primarily composed of calanoid copepods (zooplankton). Subadult and adult stages see an increase in dietary diversity to include planktonic crustaceans, fishes, and squid.[16]
Firefly squid face high predation rates and may serve as the primary food source for some predatory species including northern fur seals, particularly during their yearly migration.[13][17] The squid spends the day at depths of several hundred meters, returning to the surface when night falls. It uses its abilities to sense and produce light for counter-illumination camouflage: it matches the brightness and colour of its underside to the light coming from the surface, making it difficult for predators to detect it from below.[18] As a participant in diel vertical migration, firefly squid primarily feed during the night.[14][15] This feeding strategy is reflected in the squid’s gut anatomy, which has a longer cecum that allows it to absorb nutrients during the day when its metabolic rate is lower.[14][15]
The firefly squid resides in the deep waters of the Western Pacific Ocean where limited amounts of visual light penetrate from the surface and are bioluminescent. The shorter wavelengths of visible light are blue, green, and yellow. These shorter wavelengths have more energy and can penetrate deeper into the water column. The squid’s visual system is adapted to capture the greatest amount of light at these depths. Each eye has a large pupil to allow more ambient light to enter the eye, no cornea to reduce or distort absorbed light, a spherical lens to greatly limit distortion (coma and astigmatism), and a predominant visual pigment, retinal (A1) with a maximal absorption at 482 nm.[19]
Chemical and structural analysis of the firefly squid retina reveal the presence of three visually active pigments located in distinct regions of the squid’s retina. This is unique among cephalopods and may allow these squid to have color discrimination vision.[20][21] The presence of two or more visually active pigments have only been found in the eyes of other organisms capable of color discrimination.[22] The three pigments found include retinal (A1) with maximal absorption at 482 nm, hydroxyretinal (A4) with maximal absorption at 470 nm, and dehydroretinal (A2) with maximal absorption at 500 nm. Scanning electron microscopy shows that each pigment is contained in individual retinal photoreceptor cells which allows segregation of each pigment to specific locations on the squid retina.[20] Light of specific wavelengths need to reach the specific photoreceptive cells in the retina to avoid longitudinal spherical aberration (LSA). Cone cells of the vertebrate retina are clustered in the same retinal location and use multifocal lenses to refract the wavelengths to activate the specific photoreceptor cells. Firefly squid do not have multifocal lenses, but use a banked retina –specific photoreceptive cells are located at different distances from the lens – to compensate for LSA.[19]
Cephalopods species have historically been polyandrous, in which a female mates with multiple mates, through common reproductive traits and life history.[23] Firefly squid show rare evidence of cephalopod monogamy in their reproductive cycle when they make a yearly migration to the coastal waters of Toyama Bay each spring during their mating season. For example, females store sperm for long periods in bilateral pouches under the neck collar, and are capable of egg spawning after the breeding season when males are no longer present.[24] Males show specific sperm production and release patterning to augment their reproductive success. One proposed explanation for this unusual behavior is that although the males reach sexual maturity prior to the breeding season, females do not reach full maturity until later in the season. As a result of the shorter life-span of males, most males are only able to copulate once and are largely gone by the time that females are able to use the sperm stored during copulation.[13] Once the squid's eggs have been fertilized and laid, it dies, having reached the end of its one-year lifespan. Spawning, which involves large aggregations of the squid, takes place between February and July.[1]
Research was conducted in 2020 around the Oki Islands in the Sea of Japan, a prevalent mating ground for W. scintillans, during the estimated mating period (EMP) of mid-February to mid-March to test the firefly squid monogamy hypothesis. Researchers found that mated females stored an equivalent amount of sperm in both pouches surrounding their seminal receptacles.[24] They also observed a gradual decrease in the quantity of sperm during the reproductive season.[24] This data indicates the preservation of sperm through the lifespan of the female firefly squid. Researchers found that 95% of females tested stored sperm from a single male.[24] Further data collection confirmed that a single male's sperm fertilized all of the female's eggs.[24] Both of these findings support monogamous reproduction of W. scintillans. To test monogamy in male firefly squids, researchers measured the maturity and fecundity of individuals. Data show that average male sperm levels would allow for no more than 2-3 copulations.[24] The evidence for a low sperm production capacity and limited mating opportunities for males based on biased operational sex ratio and a lack of female remating supports the monogamy hypothesis in males. Female monandry was established first and subsequently males followed suit to create mutual monogamy in W. scintillans.[25]
Fishers have long known that firefly squid congregate in Toyama Bay off the Japanese coast to spawn. They are often caught at night when they rise to the surface or in fishing nets that trawl mesopelagic depths during the day. Commercial consumption of the W. scintillans is largely driven by the flashing blue display of photophores that makes them considered a menu prized item at restaurants. This squid is commercially fished in Japan, accounting for an annual catch of 4,804 to 6,822 tons from 1990 to 1999.[26]
Storage of W. scintillans has been difficult due to their adaptation to a deep sea environment that is notably cold and dark. Researchers found that long-term sedation (3+ days) of firefly squid can be accomplished using magnesium sulphate with relatively no harm being conferred to the organisms.[27] W. scintillans quickly returned to its normal state only minutes after being transferred into fresh seawater at the final destination.[27] The transported animals maintained their photophore-flashing capabilities, a key focus for researchers.[27]
The firefly squid (Watasenia scintillans), also commonly known as the sparkling enope squid or hotaru-ika in Japan, is a species of squid in the family Enoploteuthidae. It is the sole species in the monotypic genus Watasenia. These tiny squid are found on the shores of Japan in springtime during spawning season, but spend most of their lives in deeper waters between 200 and 400 metres (700 and 1,300 feet; 100 and 200 fathoms). They are bioluminescent organisms and emit blue light from photophores, which some scientists have hypothesized could be used for communication, camouflage, or attracting food, but it is still unclear in the scientific community exactly how this species uses their bioluminescence. The firefly squid is a predator and actively hunts its food, which includes copepods, small fish, and other squids. The lifespan of a firefly squid is about one year. At the end of their lives, females return close to shore to release their eggs and then die shortly thereafter. This mass migration of firefly squid to the shore is a lucrative business for Japanese fishermen, and during spawning season many go out to the bays to collect the dying squid. Many more also visit Japan during spawning season to see the bright blue light created from the firefly squid's bioluminescence light up the bay, making their spawning season not only a fishing opportunity but also a tourist attraction.
El calamar luciérnaga (Watasenia scintillans),[1] también conocido como el calamar enope brillante, es una especie de calamar de la familia Enoploteuthidae. Es la única especie del género monotípico Watasenia.
Bioluminiscencia y contrailuminación
El calamar luciérnaga se encuentra en el océano Pacífico occidental a profundidades de 183 a 366 metros (600–1200 pies) y es bioluminiscente. El manto, la cabeza, los brazos y los tentáculos están salpicados de pequeños órganos productores de luz llamados fotóforos. Cuando parpadea, la luz atrae a los peces pequeños, de los que los calamares pueden alimentarse. Este calamar tiene tres pigmentos visuales ubicados en diferentes partes de la retina que probablemente permiten la discriminación del color, cada uno con sensibilidades espectrales distintas. El calamar luciérnaga mide aproximadamente 3 pulgadas (7,6 cm) de largo en la madurez y muere después de un año de vida. Tiene los ocho brazos estándar y dos tentáculos, cada uno con tres órganos brillantes que emiten luz en las puntas.
El calamar pasa el día a profundidades de varios cientos de metros, volviendo a la superficie cuando cae la noche. Utiliza sus habilidades para detectar y producir luz para el camuflaje de contrailuminación: combina el brillo y el color de su parte inferior con la luz que proviene de la superficie, lo que dificulta que los depredadores la detecten desde abajo.
El calamar luciérnaga (Watasenia scintillans), también conocido como el calamar enope brillante, es una especie de calamar de la familia Enoploteuthidae. Es la única especie del género monotípico Watasenia.
Watasenia scintillans, anche conosciuto come il calamaro lucciola, è una specie di calamaro della famiglia Enoploteuthidae[1]. È la sola specie del genere Watasenia.
Il calamaro lucciola è stato osservato nella parte ovest dell'oceano Pacifico ad una profondità tra i 183 ed i 366 metri. La caratteristica più peculiare di questa specie è la bioluminescenza: ogni tentacolo ha un organo chiamato fotoforo il quale produce luce. Queste luci attraggono i piccoli pesci dei quali il calamaro si nutre.
Questo calamaro è l'unica specie di cefalopode nel quale si siano trovate prove di visione a colori: ha tre pigmenti visivi localizzati in differenti parti della retina che gli permettono probabilmente di discriminare i colori, ciascuno con una distintivo spettro di sensibilità.
Il calamaro lucciola misura circa 7,5 cm alla maturità e muore dopo solo un anno di vita. Ha i classici tentacoli otto più due tipici dei calamari, di cui un paio ha tre organi per l'emissione di luce all'estremità.
Il calamaro trascorre il giorno a varie centinaia di metri di profondità, ritornando in superficie durante la notte. La combinazione di organi per la percezione e l'emissione di luce gli permette di nascondere il suo profilo in superficie (controillunimazione), rendendo difficile per i predatori individuarlo dal basso.
Il calamaro lucciola può anche illuminare il suo corpo per attrarre il partner. La stagione degli accoppiamenti dura da marzo a giugno.
Questo calamaro è pescato in Giappone. Si calcola che annualmente (dal 1990 al 1999) siano state pescate dalle 4804 alle 6822 tonnellate.
Watasenia scintillans, anche conosciuto come il calamaro lucciola, è una specie di calamaro della famiglia Enoploteuthidae. È la sola specie del genere Watasenia.
Watasenia scintillans is een soort in de taxonomische indeling van de inktvissen, een klasse dieren die tot de stam der weekdieren (Mollusca) behoort. De inktvis komt enkel in zout water voor en is in staat om van kleur te veranderen. Hij beweegt zich voort door water in zijn mantel te pompen en het er via de sifon weer krachtig uit te persen. De inktvis is een carnivoor en zijn voedsel bestaat voornamelijk uit vis, krabben, kreeften en weekdieren die ze met de zuignappen op hun grijparmen vangen.
De inktvis komt uit het geslacht Watasenia en behoort tot de familie Enoploteuthidae. Watasenia scintillans werd in 1911 beschreven door Berry.[1]
Bronnen, noten en/of referentiesWatasenia scintillans[6][7][9][10], ibland omnämnd som eldflugebläckfisk,[11] är en bläckfiskart som först beskrevs av Samuel Stillman Berry (1887-1984) 1911. Watasenia scintillans ingår i släktet Watasenia och familjen Enoploteuthidae.[12][13] Inga underarter finns listade i Catalogue of Life.[12]
Arten finns (bland annat) i vattnen runt Japan.[11] I samband med äggläggningen beger sig dessa i vanliga fall djuphavslevande djuren upp mot vattenytan under mars–maj varje år. Efter äggläggningen dör honorna sedan. De är i Japan föremål för fiske.
Denna bläckfisk är känd för sin bioluminiscens, vilken åstadkoms genom tusentals små ljusalstrande organ. Ljuset gör att bläckfisken lättare smälter in i den vanligtvis grå omgivningen, åtminstone sedd underifrån.[14]
Varje år mellan mars och maj glittrar vattnet i japanska Toyamabukten som en diskokula. Det som blänker så festligt är miljontals sju centimeter långa fiskar (watasenia scintillans, på engelska firefly squid, "eldflugebläckfisk"). Fiskarnas kroppar blinkar och pulserar i starkt blått.
Watasenia scintillans, ibland omnämnd som eldflugebläckfisk, är en bläckfiskart som först beskrevs av Samuel Stillman Berry (1887-1984) 1911. Watasenia scintillans ingår i släktet Watasenia och familjen Enoploteuthidae. Inga underarter finns listade i Catalogue of Life.
Arten finns (bland annat) i vattnen runt Japan. I samband med äggläggningen beger sig dessa i vanliga fall djuphavslevande djuren upp mot vattenytan under mars–maj varje år. Efter äggläggningen dör honorna sedan. De är i Japan föremål för fiske.
Denna bläckfisk är känd för sin bioluminiscens, vilken åstadkoms genom tusentals små ljusalstrande organ. Ljuset gör att bläckfisken lättare smälter in i den vanligtvis grå omgivningen, åtminstone sedd underifrån.
Varje år mellan mars och maj glittrar vattnet i japanska Toyamabukten som en diskokula. Det som blänker så festligt är miljontals sju centimeter långa fiskar (watasenia scintillans, på engelska firefly squid, "eldflugebläckfisk"). Fiskarnas kroppar blinkar och pulserar i starkt blått.
螢火魷(学名:Watasenia scintillans),又名螢魷或螢烏賊[2],为武裝魷科下的一个物种,屬於只有本身的螢火魷屬。牠是一種非常小的魷魚,通常有3英寸(7.6厘米)長。和其他深海生物一樣可以發光,這些光可用來引誘獵物。萤火鱿多分布于日本海及日本四国以北的太平洋沿近海[3]。
萤火鱿于西太平洋海域被发现,水深约183至366公尺(600-1200英尺)处。这种鱿鱼的每根触鬚都有一个发光器产生萤光,进而引诱猎物。据报导,此种鱿鱼是其物种中唯一能辨别颜色者,牠拥有3个类似视网膜的器官,每个具有不同光谱频率的感光度[4]。萤火鱿身长大约3英寸(7.6厘米),寿命长约一年,拥有标准的8条触腕和2条触足。此鱿鱼一整天都待在百公尺深的海裡,只有夜晚才会来到海面附近,在体内的发光器与感光器作用下,牠可依照深度来调整自身的亮度。
其交配其为每年3月至6月,手法即是发出萤光来吸引异性。
萤火鱿在日本属于商业渔获,据统计,从1990年至1999年间,日本约捕获了4,804-6,822吨的萤火鱿[5]。日本本州富山县富山湾为此渔获的主要供应地,因为富山湾的深层水域蕴含丰富的矿物质及有机物[6],加上富山灣靠岸處還有一個V字型海谷,時常會有湧昇流由下往上帶,將螢火魷推上岸邊[7],因此萤火鱿在每年3至6月皆会到此产卵[7],富山县即因大量产此渔获而将萤火鱿选为「县鱼」[8]。
日本的学者发现,萤火鱿不仅美丽,还含有丰富的牛磺酸,可帮助降低胆固醇[6]。萤火鱿相关研究者不多,有美国学者2002年发表一篇萤火鱿发光机制的论文,但在2008年4月遭到推翻[9];推翻者为2008年诺贝尔化学奖得主、前海洋生物研究室(Marine Biological Laboratory)资深研究员下村脩,及日本三重大学研究所生物资源学研究科教授寺西克伦[9]。不过,虽然下村脩已研究萤火鱿有40年之久,其二人至今仍无法解开萤火鱿发光机制之谜[9]。
|access-date=
中的日期值 (帮助) 螢火魷(学名:Watasenia scintillans),又名螢魷或螢烏賊,为武裝魷科下的一个物种,屬於只有本身的螢火魷屬。牠是一種非常小的魷魚,通常有3英寸(7.6厘米)長。和其他深海生物一樣可以發光,這些光可用來引誘獵物。萤火鱿多分布于日本海及日本四国以北的太平洋沿近海。
ホタルイカ(螢烏賊/蛍烏賊、学名Watasenia scintillans (Berry, 1911)[1])は、ツツイカ目 ホタルイカモドキ科に属するイカの一種である。後述のように食用とされる。
ホタルイカの属名Watasenia は1905年に和名を「ホタルイカ」と命名した明治期の生物学者渡瀬庄三郎にちなんで1913年に石川千代松によりつけられている[2]。富山の方言では「マツイカ」と呼ばれることが多かった。これはホタルイカが松の肥料として利用されることが多かったからとされる。
英名の一つであるfirefly squidは和名と同じく「ホタルのようなイカ」の意味で、toyama squidは日本の代表的な産地である富山湾に因む。米『ウェブスター辞典』のfirefly squidの項目には"a brilliantly luminescent squid (Watseonia scintillans) caught in great quantities off the western coast of Japan where it is used for fertilizer"と記載されている。冷蔵・運送が近代化される前は、地元での食用以外は、流通前に肥料として多く利用されたためである。
世界にはホタルイカの仲間が40種類ほど生息している。
日本近海では日本海全域と太平洋側の一部に分布しており、特に富山湾に面する滑川市を中心とする富山県と、兵庫県の日本海側で多く水揚げされている。ホタルイカというと富山湾をイメージする人は多いが、漁獲量は兵庫県の浜坂漁港が日本一(2017年で2734トン)で、富山県全体(同1299トン)を上回る[4]。普段は水深200m - 700mの深海に生息している。晩春から初夏までが産卵期で、1回当たり数千個から1万個の卵を産む。交尾と産卵は同時ではない。
触手の先には、それぞれ3個の発光器が付いている。何かに触れると発光するため、敵を脅すものではないかと考えられているが、光によって敵を誘導し、ただちに消灯してその場から逃げるという、いわばデコイとしての機能があるともされている[5]。体表の海底側(腹側)には細かい発光器があり、これは海底側にいる敵が海面側にいるホタルイカを見ると、海面からの光に溶け込み姿が見えなくなるカウンターシェイディング効果の役割を果たしている。海面側から海底に向かって見た場合はこの効果が働かないため、体表の海面側(背中側)には発光器はほとんど存在しない。
発光反応の全容は未解明である。しかし、「セレンテラジンジサルファイト化合物(coelenterazine disulfate、二硫化セレンテラジン化合物、ルシフェリンの一種)によると考えられており、アデノシン三リン酸(ATP)とマグネシウム(Mg)が大きく関与している」。また、「発光反応の最適温度は、5℃でホタルイカの生息適温と対応している」などが判明している[6]。
主に食用となるほか、養殖マグロの飼料用途への研究がされている[7]。
漁期は2月から5月頃、主な産地は日本海側の兵庫県、富山県、鳥取県、福井県などである。
富山県では古くから食用とされ、炒め物、佃煮を含む煮物、酢味噌和え、沖漬け、素干し、天ぷら、唐揚げ、足だけを刺身にした竜宮そうめんなどがある[12]。腐敗が早いため冷凍・冷蔵での高速輸送手段が発達するまで、産地以外での食用は困難だった。現代では、首都圏など水揚げ漁港から遠い地域の食品スーパーマーケットや鮮魚店で販売されるほか、居酒屋や回転寿司店[13]などで提供される。
傷みやすいことによる食中毒や、後述するような寄生虫の虞があるため、古くより食してきた地元でも生では食べなかった。平成になってから、冷凍などの処理をしたものが生食用として春先の店頭に並ぶことが多くなっている(生食の注意点については後述)。
食味や旬の漁獲高が多いことだけでなく、近年は栄養面でも評価されている。富山短期大学教授の竹内弘幸(食品機能学)の分析によると、ビタミンAやビタミンB12、タウリンを多く含む[14]。
刺身と竜宮そうめん(ほたるいかミュージアムにて)
漫画『美味しんぼ』第37巻収録の「生きた宝石」[15]で、ホタルイカについて生きたまま食べる描写(ホタルイカの踊り食い)がなされている[16][17]。作中では肝のおいしさが絶賛されているが、ホタルイカには旋尾線虫亜目に属する旋尾線虫( Crassicauda giliakiana )[18][19]が寄生しているため、生食の際は厚生労働省が指定した方法で処理を行う必要がある。未処理品の「踊り食い」や処理が不完全な物を食用とした場合、後述の寄生虫症を発症することがある[20]。
生食により寄生虫症を発症し、急性腹症として腸閉塞、皮膚爬行症、眼球移行症などを起こすことがある[21]。国立感染症研究所によれば、最初の症例報告は1974年の秋田県での腸閉塞の疑い例とされている。その後、報告は1987年まで途絶えるが以降1994年までに約50例が報告され注目された。診断は摘出虫体の病理組織学的同定(とり出して調べる)。治療法は今のところ外科的摘出(広い目にメスを入れて引っ張りだす)のみ。
ホタルイカが水揚げされる富山県の富山市から魚津市にかけての富山湾沿岸は、ホタルイカの群遊海面として有名であり、ホタルイカは春の風物詩として知られている。富山湾に流入する常願寺川の河口左岸から魚津港までの約15km、満潮時の沖合1,260mまでの海域は1922年(大正11年)に国の天然記念物に指定され、1952年(昭和27年)3月29日には「ホタルイカ群遊海面」の名称で特別天然記念物に格上げされている[25]。天然記念物指定を「ホタルイカ」とすると食用にはできないために、「群遊海面」としたのである。
前述のように、富山湾でのホタルイカ定置網漁の様子は観光船から見学できる。
4-5月の富山湾沿岸では、「ホタルイカの身投げ」と呼ばれる、大量のホタルイカが波によって浜に打ち寄せられる現象が、夜中から夜明け前の暗がりの中で幻想的に見られることがあり[26]、県民が波打ち際や堤防などから網ですくい持ち帰る様子が見られる。
富山県滑川市には、ホタルイカの様子を観察できる「ほたるいかミュージアム」がある。
富山湾を上回る漁獲量がある浜坂でも毎春「浜坂みなとほたるいか祭り」を開いている[27]。
ホタルイカは1966年(昭和41年)7月1日発売の35円普通切手の意匠になった。