The splitfin flashlightfish or two-fin flashlightfish (Anomalops katoptron) is a species of schooling reef fish in the family Anomalopidae. It is found in warm waters in the central and western Pacific Ocean near reefs 200–400 m (660–1,300 ft) in depth.[1] It can grow to a length of 35 cm (14 in) TL. It is the only known member of the genus Anomalops.[2] It is listed under the IUCN as a species of least concern.
| Splitfin flashlightfish | |
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Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Trachichthyiformes |
| Family: | Anomalopidae |
| Genus: | Anomalops Kner, 1868 |
| Species: | A. katoptron
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| Binomial name | |
| Anomalops katoptron (Bleeker, 1856)
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Description
editThe splitfin flashlightfish is characterized by a black body with a blue tinge along the dorsal and caudal fins. Adults can reach up to 35 cm (14 in) TL in length[2] but on average measure anywhere between 10 cm to 30 cm (4-12 in).[3] It has a slightly laterally compressed deep body with an upwards terminal mouth and narrow caudal peduncle. It has two separate dorsal fins: the anterior portion consisting of 6-7 dorsal spines and the posterior portion consisting of 14-15 soft dorsal rays. Its anal fin contains 2 spines and 9-11 soft rays.
Its most prominent features are the two bean shaped torch-like organs under its eyes containing symbiotic bioluminescent bacteria Candidatus photodesmus katoptron, which the fish can turn on and off by blinking. The light organs are embedded in suborbital cavities and are connected at the anterior edge via a cartilaginous rod-like attachment. The suborbital light organs are densely settled with luminous symbiotic bacteria that grow in tubular structures and produce a constant bluish light of around 500 nm in wavelength.[4] One face of these organs is black, whereas the other is luminous. To turn ‘on’ its light, A. katoptron rotates the organ length-wise so that the luminous face is exposed to the outside. To turn ‘off’ its light, it then rotates the luminous face down towards the body, presenting the black pigmented face outwards.[5] This is a vastly different and unique rotating mechanism for manipulating its eye organs, as most other related flashlight fish have a ‘shutter’ mechanism.
The bioluminescent bacteria Candidatus photodesmus katoptron has only been recently discovered in 2011 as symbiotic with A. katoptron, meaning that it can only survive in its host. There are no known lab-cultivated populations of the bacteria.[7] The size of the bacterial genome is relatively small compared to others in the Vibrionaceae genus. The inability to grow under laboratory conditions can be attributed to this genome reduction and gene loss.[8] Via thorough phylogenetic analysis, the splitfin flashlightfish and its symbiont are a key example highlighting rapid co-evolution and population bottlenecks that suggest an obligately dependent relationship. However, a mechanism by which anomalopid bacteria transfer between host generations is still unknown.[7]
Distribution and habitat
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Splitfin flashlightfish are found in the western and central Pacific Ocean from the Philippines and Indonesia east to the Tuamotus, north to Japan, and south to the Great Barrier Reef. It is generally found near drop-offs and caves 200–400 m (660–1,310 ft) in depth,[2] but will move into shallower waters during the winter months.[9]
Biology and ecology
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A nocturnal species, the splitfin flashlightfish avoids sunlight[9] and seeks prey in dark areas. It feeds primarily on zooplankton.[2] Individuals can be found in large schools during moonless nights in the shallow water of coral reefs and in the open surrounding water.[4]
Its bioluminescent organs serve a functional purpose in searching for and detecting planktonic prey. Researchers have found that in darkness (periods of activity), A. katoptron has high blink frequencies and increases the amount of time light organs are on. Paired with their schooling behavior, this high blinking frequency can confuse and deter predators. During the day (periods of inactivity), A. katoptron reduces blink frequency and decreases the amount of time light organs are on. When in the presence of prey, A. katoptron emits a constant glow from their light organs, effectively illuminating their meal. This, however, presents a trade off by making themselves more vulnerable to predators.[4]
Changes in eyeshine and occlusion of the eye organ also elucidates the possibility of a communication system among fish.[10] Further research has revealed that the blinking mechanism of the splitfin flashlightfish also assists in keeping a cohesive school of fish together. Intraspecific communication between A. katoptron is crucial for the movement of a school of fish. In addition to lateral line sensing, blinking of the light organs also aids A. katoptron in determining the distance between itself and its nearest neighbor in a school.[11] A well communicating school best avoids predators and preys on food.
Despite its important functionality, bioluminescence can be lost in A. katoptron if faced with starvation. Observations suggest that this is because of reduced nutrients in the bloodstream, which ultimately supplies the light organs in parallel running capillaries. This highlights the symbiotic dependence between A. katoptron and its light-emitting bacteria.[12]
There is very little known about the reproduction of the splitfin flashlightfish. It is believed that they are broadcast spawners.[3] This type of spawning involves eggs and sperm being released into the water column where external fertilization occurs.
In the aquarium
editThis fish can be found in the aquarium trade. It can be kept with other nocturnal fish, including pinecone fish, glasseye squirrelfish, and cardinalfish. This species requires plenty of hiding places and low lighting in the aquarium.[13] Bioluminescence may be lost in captive A. katoptron, but experimental husbandry efforts by the Toledo Zoo have demonstrated that providing adequate food, maintaining stable temperatures, and adding occasional bacterial cultures of Vibrio fischeri (a marine photobacterium) may help the fish regain and/or retain the desired luminosity for viewers.[14] Spawning of the related flashlightfish Photoblepharon palpebratum in an aquarium was observed by Meyer-Rochow in 1976.[15]
There is very little known about the reproduction of the splitfin flashlightfish. It is believed that they are broadcast spawners.[3] This type of spawning involves eggs and sperm being released into the water column where external fertilization occurs.
References
edit- ^ Bray, Dianne J. (2011). "Twofin Flashlightfish, Anomalops katoptron". Fishes of Australia. Museums Victoria. Retrieved 20 February 2016.
- ^ a b c d e Froese, Rainer; Pauly, Daniel (eds.). "Anomalops katoptron". FishBase. February 2017 version.
- ^ a b c Pacific, Aquarium of the. "Splitfin Flashlight Fish". www.aquariumofpacific.org. Retrieved 2024-11-07.
- ^ a b c d Hellinger, Jens, Peter Jägers, Marcel Donner, Franziska Sutt, Melanie D. Mark, Budiono Senen, Ralph Tollrian, and Stefan Herlitze. "The Flashlight Fish Anomalops Katoptron Uses Bioluminescent Light to Detect Prey in the Dark." PLOS ONE. Public Library of Science, n.d. Web. 03 May 2017
- ^ Haneda, Yata; Tsuji, Frederick I. (1971-07-09). "Light Production in the Luminous Fishes Photoblepharon and Anomalops from the Banda Islands". Science. 173 (3992): 143–145. doi:10.1126/science.173.3992.143. ISSN 0036-8075.
- ^ JOHNSON, G. DAVID; ROSENBLATT, RICHARD H. (1988). "Mechanisms of light organ occlusion in flashlight fishes, family Anomalopidae (Teleostei: Beryciformes), and the evolution of the group". Zoological Journal of the Linnean Society. 94 (1): 65–96. doi:10.1111/j.1096-3642.1988.tb00882.x. ISSN 0024-4082.
- ^ a b Hendry, Tory A.; Dunlap, Paul V. (2011-12-01). "The uncultured luminous symbiont of Anomalops katoptron (Beryciformes: Anomalopidae) represents a new bacterial genus". Molecular Phylogenetics and Evolution. 61 (3): 834–843. doi:10.1016/j.ympev.2011.08.006. ISSN 1055-7903.
- ^ Dunlap, Paul (2014), Thouand, Gérald; Marks, Robert (eds.), "Biochemistry and Genetics of Bacterial Bioluminescence", Bioluminescence: Fundamentals and Applications in Biotechnology - Volume 1, Berlin, Heidelberg: Springer, pp. 37–64, doi:10.1007/978-3-662-43385-0_2, ISBN 978-3-662-43385-0, retrieved 2024-11-08
- ^ a b Grzimek, Bernhard (2003). Michael Hutchins (ed.). Grzimek's Animal Life Encyclopedia, Fishes II. Vol. 5 (2nd ed.). Farmington Hills: Gale. p. 118. ISBN 978-0787657819.
- ^ Howland, Hoard C.; Murphy, Christopher J.; Mccosker, John E. (1992-04-01). "Detection of eyeshine by flashlight fishes of the family anomalopidae". Vision Research. 32 (4): 765–769. doi:10.1016/0042-6989(92)90191-K. ISSN 0042-6989.
- ^ Jägers, Peter; Wagner, Louisa; Schütz, Robin; Mucke, Maximilian; Senen, Budiono; Limmon, Gino V.; Herlitze, Stefan; Hellinger, Jens (2021-03-19). "Social signaling via bioluminescent blinks determines nearest neighbor distance in schools of flashlight fish Anomalops katoptron". Scientific Reports. 11 (1): 6431. doi:10.1038/s41598-021-85770-w. ISSN 2045-2322. PMC 7979757. PMID 33742043.
- ^ Meyer-Rochow, V. B. (1976). "Loss of bioluminescence inAnomalops katoptron due to starvation". Experientia. 32 (9): 1175–1176. doi:10.1007/BF01927610. ISSN 0014-4754.
- ^ Anomalops katoptron. The Fish Index.
- ^ Hemdal, Jay (1992). "Captive husbandry of the flashlight fish, Anomalops katoptron (Bleeker 1856)". Journal of Aquariculture & Aquatic Sciences.
- ^ Meyer-Rochow, V.B. (1976), "Some observations on spawning and fecundity in the luminescent fish Photoblepharon palpebratus", Marine Biology, 37 (4): 325–328, Bibcode:1976MarBi..37..325M, doi:10.1007/bf00387487, S2CID 84779819
External links
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Media related to Anomalops katoptron at Wikimedia Commons
Data related to Anomalops katoptron at Wikispecies
