Mueller's pearlside
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Stomiiformes
Family: Sternoptychidae
Genus: Maurolicus
Species:
M. muelleri
Binomial name
Maurolicus muelleri
(J. F. Gmelin, 1789)

Maurolicus muelleri, commonly referred to as Mueller's pearlside, Mueller's bristle-mouth fish (not to be confused with the Gonostomatidae), or the silvery lightfish (not to be confused with the Phosichthyidae), is a marine hatchetfish in the genus Maurolicus, found in deep tropical, subtropical and temperate waters of the Pacific Ocean and the Atlantic Ocean, from the surface to depths of 1,500 metres (4,900 ft). It can grow to a maximum total length of 8 centimetres (3.1 in).[2]

Distribution and habitat

Maurolicus muelleri is found across the Pacific and Atlantic Oceans from subpolar waters to the equator, as well as in the Mediterranean, however they are absent in the Indian Ocean.[2] M. muelleri is most abundant around bathymetric features such as seamounts and continental shelf breaks, and is scarce in the open ocean. This species is predominantly found at depths of around 150 to 250 metres (490 to 820 ft) during the day, but can be found as shallow as 50 metres (160 ft) during the nighttime.[2] They can be found in depths of at least 1,527 metres (5,010 ft) at maximum.[2] It lives in tropical, subtropical and temperate waters in the deep sea.[2]

Description

Ventral view of M. muelleri, showing the photophores used for counterillumination.
Maurolicus muelleri fresh specimen
Fresh-caught specimen of Maurolicus muelleri

Maurolicus muelleri has a fusiform body shape with a moderately sized, subvertical mouth. M. muelleri is countershaded to provide camouflage in the open-ocean, with a dark dorsal surface, silvered flanks and clustered photophores on the ventral surface for counterillumination. In fresh-caught specimens, these photophores are coloured a light pink/purple. They have 9 to 12 dorsal fin rays, 17-19 pectoral fin rays, 7 pelvic fin rays and 22 to 28 anal fin rays.[3] They can grow up to 8 centimetres (3.1 in) at maximum length, but usually grows up to 4 centimetres (1.6 in).[2]

Photophores

Photophores are glandular organs that, in M. muelleri, are made up of several parts. The photogenic chamber, made up of small, spherical light-producing cells, is split into a subspherical tank and conic projector, embedded inside a reflector made of guanine crystals. Ventral to the photogenic chamber is a cellular lens that is itself covered on the ventral surface by a gelatinous dioptric layer.[4]

Eyes

Maurolicus muelleri has large eyes with a retina uniquely adapted to the animal's mesopelagic habitat. M. muelleri inhabits surface waters only during twilight hours, requiring acute mesopic vision which in most vertebrates is achieved through combining dim-light rod cells and bright-light cone cells. Fish in the genus Maurolicus have developed a unique photoreceptor where a cone opsin and phototransduction cascade is found in cells transmuted into a rod-like morphology. These rod-like cone receptors are tuned to the blue-shifted mesopic light conditions dominant in M. muelleri's habitat and are likely a more efficient method of mesopic vision than would be feasible with two improperly-functioning photoreceptor types.[5]

Ecology

Trophic ecology

Mueller's pearlside is a zooplanktivore, with exact diet composition varying geographically and seasonally. For example, Copepods are the main constituent of their diet in the Sea of Japan[6] and in waters surrounding Korea,[7] with the euphausiid species Euphausia pacifica of secondary importance near Japan.[6] Euphausiids and copepods are the dominant prey items year-round off near the eastern continental slope of Tasmania.[8] In Masfjorden, Norway, copepods are most important in the autumn,[9] while earlier in the year Cladocerans are most important.[10] Amphipods and pteropods have also been reported from stomach contents.[6]

Maurolicus muelleri inhabits a tertiary trophic position[6] and, as such, provides a trophic link between zooplankton and larger predators. A wide range of fish species prey on M. muelleri, including commercially-important species such as albacores, skipjack tuna, hake, and blue whiting.[11][12][13][14] They are also predated on by several cephalopods, including the squids Illex coindetii and Todaropsis eblanae[15] and the octopus Enteroctopus magnificus[16], and marine mammals including common dolphins, sei whales, Bryde's whales, and fin whales.[11][17][18][19]

Parasitology

Due to its trophic position, M. muelleri plays a role as an intermediate or paratenic host to a variety of parasitic taxa, with very few parasites reaching adulthood while infecting the pearlside. For example, in a study that examined 1329 individual Maurolicus muelleri specimens, 3720 parasites were found with only 5 individual adult parasites.[20] Endoparasites recorded from Maurolicus muelleri include the trematodes Derogenes varicose, Brachyphallus crenatus, and Lecithaster confusus, cestodes including Bothriocephalus sp. and Scolex pleuronectis, the nematodes Hysterothylacium aduncum and Anisakis simplex[20][21]. One of the only species to reach adulthood parasitising M. muelleri is the ectoparasitic copepod Sarcotretes scopeli.[20] A "fungoid mass", tentatively identified as being from the protist genus Ichthyophonus, has been identified in pearlsides caught near Australia.[22]

Behavior

Diel vertical migration

As with many mesopelagic species, Maurolicus muelleri undergoes diel vertical migration (DVM), however this behaviour is more complex and varied in M. muelleri than that descriptor usually entails. The specific nature of this migration can vary seasonally, between years, an across geography, as well as across the ontogeny of individual fishes.[23]

The vertical migration of M. muelleri has been best studied in Masfjorden, where a fifteen-month acoustic survey was undertaken. In Masfjorden, M. muelleri formed distinct scattering layers, with the deepest layer composed of adults and a shallow layer composed of post-larvae.[23] The depth of these scattering layers is thought to be a result of M. muelleri having a "light comfort zone", inhabiting depths where light levels are neither too bright nor too dark. Individual fish may move between scattering layers, indicating that the comfort zones are broader than suggested in the typical isolume hypothesis.[24] Here, M. muelleri displayed consistent, typical DVM patterns (i.e. remaining at depth during the day and ascending to the surface at night) during summer months only, with individuals feeding at dawn and dusk.[23]

Their behaviour, however, varied in the autumn and winter. In years where their Calanus copepod prey, which overwinter at depth, were abundant, adults in the winter delayed their vertical migration until approximately three hours before dawn due potentially to a reduced need to feed at the surface, with some individuals remaining at depth for the entire night, feeding entirely on deep-overwintering prey. Towards the end of the winter, adults underwent interrupted ascents, migrating to depths that were greater than reached during typical DVM as they preyed on deep-wintering prey partway through their seasonal ascent to the surface. Some individuals undertook a reversed DVM during winter, diving to slightly greater depths during daylight hours, to feed on deep-overwintering prey in optimal light conditions.[23] In the Benguela system and in the Gulf of Oman, DVM is known to occur, with fish ascending to within 10m of the surface in response to the first light of dawn before diving into deep waters.[25]

Predator evasion

In latitudes where summer nights are short and bright, such as in the Arctic Circle, M. muelleri may school in shallow waters at night to reduce the threat of predation.[26] Maurolicus muelleri in scattering layers can detect predators at distances of several metres during the day, and respond by diving as far as 50m below their original depths at speeds of 15–20 cm/s.[24] While most individuals reside in scattering layers to reduce predation risk, certain "bold individuals" will make forays into shallower waters above scattering layers, presumably in order to feed in move favourable light levels. It is unknown whether these bold individuals are atypical or whether a change in individual state (e.g. hunger) prompts these forays.[24]

Life History

Spawn timing in Maurolicus muelleri is regionally variable. In the Benguela system, breeding occurs year round, while in Australia spawning occurs in late winter and early spring.[22][27] In Norway, spawning occurs between March and September,[28] however hatch timing is a strong predictor of recruitment success, with individuals hatching before mid-September experiencing poor conditions for growth.[29] Females mature at lengths of around 35mm, at the end of their first year, and fish below 30mm cannot be sexed.[22] A small fraction of individuals survive into their second year, reaching lengths of up to 50mm in Australia.[22]

Individual females can contain as many as 738 ova,[22] and in enclosed spaces eggs can be extremely abundant, reaching numbers as high as 5.8x10^11 in Fensfjorden.[30] Eggs settle at a depth of around 200m in the Benguela system.[27] The eggs are surrounded by a distinctive hexagonal-patterned membrane.[22]

Importance to Fisheries

At present, M. muelleri is of minor importance to fisheries, with several countries, including Russia, Iceland, and the Faroe Islands attempting to pursue it as a resource after the collapse of other fisheries, with no nation landing more than 50,000 tonnes in a single year.[1] The species continues to be a focus of speculation for future mesopelagic fisheries,[31] however a number of technical hurdles will need to be surmounted in order to make pearlsides a cost-effective fishery target.[32]

References

  1. 1 2 A. Harold; R. Milligan (2019). "Maurolicus muelleri". IUCN Red List of Threatened Species. IUCN. 2019: e.T198760A21913754. doi:10.2305/IUCN.UK.2019-2.RLTS.T198760A21913754.en.
  2. 1 2 3 4 5 6 Froese, Rainer; Pauly, Daniel (eds.) (2006). "Maurolicus muelleri" in FishBase. March 2006 version.
  3. ↑ Peter James Palmer Whitehead (1986). Fishes of the North-eastern Atlantic and the Mediterranean. Paris: Unesco. ISBN 92-3-002215-2. OCLC 13186416.
  4. ↑ Cavallaro, M.; Mammola, C. L.; Verdiglione, R. (June 2004). "Structural and ultrastructural comparison of photophores of two species of deep-sea fishes: Argyropelecus hemigymnus and Maurolicus muelleri: comparison of photophores in two species of fishes". Journal of Fish Biology. 64 (6): 1552–1567. doi:10.1111/j.0022-1112.2004.00410.x.
  5. ↑ de Busserolles, Fanny; Cortesi, Fabio; Helvik, Jon Vidar; Davies, Wayne I. L.; Templin, Rachel M.; Sullivan, Robert K. P.; Michell, Craig T.; Mountford, Jessica K.; Collin, Shaun P.; Irigoien, Xabier; Kaartvedt, Stein; Marshall, Justin (2017-11-03). "Pushing the limits of photoreception in twilight conditions: The rod-like cone retina of the deep-sea pearlsides". Science Advances. 3 (11): eaao4709. doi:10.1126/sciadv.aao4709. ISSN 2375-2548. PMC 5677336. PMID 29134201.
  6. 1 2 3 4 Ikeda, T; Hirakawa, K; Kajihara, N (1994). "Diet composition and prey size of the mesopelagic fish Maurolicus muelleri (Sternoptychidae) in the Japan sea". Bulletin of Plankton Society of Japan. 41.
  7. ↑ Cha, Byung-Yul (1998). "Spawning ecology and feeding habits of Maurolicus muelleri". Korean Journal of Ichthyology. 10 (2): 176–183.
  8. ↑ Young, J. W.; Blaber, S. J. M. (October 1986). "Feeding ecology of three species of midwater fishes associated with the continental slope of eastern Tasmania, Australia". Marine Biology. 93 (1): 147–156. doi:10.1007/bf00428663. ISSN 0025-3162.
  9. ↑ Srisomwong, Jantra (2009). Diel vertical migration and feeding pattern of M. muelleri in Masfjorden in late autumn (Master thesis). The University of Bergen. hdl:1956/21213.
  10. ↑ Rasmussen, O. I.; Giske, J. (1994-11-01). "Life-history parameters and vertical distribution of Maurolicus muelleri in Masfjorden in summer". Marine Biology. 120 (4): 649–664. doi:10.1007/BF00350086. ISSN 1432-1793.
  11. 1 2 Hassani, S; Antoine, L; Ridoux, V (December 1997). "Diets of Albacore,Thunnus alalunga, and Dolphins,Delphinus delphisandStenella coerulaeoalba, Caught in the Northeast AtlanticAlbacore Drift-net Fishery:A Progress Report". Journal of Northwest Atlantic Fishery Science. 22: 119–123. doi:10.2960/j.v22.a10. ISSN 0250-6408.
  12. ↑ Ankenbrandt, Lisa (1985). "Food habits of bait-caught Skipjack Tuna, Katsuwonus pelamis, from the Southwestern Atlantic Ocean". Fishery Bulletin. 83 (3): 373–393.
  13. ↑ Cartes, Joan E.; Hidalgo, Manuel; Papiol, Vanesa; Massutí, Enric; Moranta, Joan (March 2009). "Changes in the diet and feeding of the hake Merluccius merluccius at the shelf-break of the Balearic Islands: Influence of the mesopelagic-boundary community". Deep Sea Research Part I: Oceanographic Research Papers. 56 (3): 344–365. doi:10.1016/j.dsr.2008.09.009. ISSN 0967-0637.
  14. ↑ Bjelland, Otte; Monstad, Terje (1997). "Blue whiting in the Norwegian Sea, spring and summer 1995 and 1996". ICES.
  15. ↑ Lordan, C.; Burnell, G. M.; Cross, T. F. (December 1998). "The diet and ecological importance ofIllex coindetiiandTodaropsis eblanae(Cephalopoda: Ommastrephidae) in Irish waters". South African Journal of Marine Science. 20 (1): 153–163. doi:10.2989/025776198784126214. ISSN 0257-7615.
  16. ↑ Villanueva, R. (June 1993). "Diet and mandibular growth ofOctopus magnificus(Cephalopoda)". South African Journal of Marine Science. 13 (1): 121–126. doi:10.2989/025776193784287239. ISSN 0257-7615.
  17. ↑ Kawamura, Akito (1973). "Food and feeding of Sei Whales in waters south of 40°N in the North Pacific". Scientific Reports of the Whale Research Institute. 25: 219–236.
  18. ↑ Best, PB (2001). "Distribution and population separation of Bryde's whale Balaenoptera edeni off southern Africa". Marine Ecology Progress Series. 220: 277–289. doi:10.3354/meps220277. ISSN 0171-8630.
  19. ↑ Bravo Rebolledo, Elisa L.; IJsseldijk, Lonneke L.; Solé, Liliane; Begeman, Lineke; de Vries, Simon; van den Boom, Louis; Camalich Carpizo, Jaime; Leopold, Mardik F. (2016-12-01). "Unorthodox Sampling of a Fin Whale's (Balaenoptera physalus) Diet Yields Several New Mesopelagic Prey Species". Aquatic Mammals. 42 (4): 417–420. doi:10.1578/am.42.4.2016.417. ISSN 0167-5427.
  20. 1 2 3 Hamre, Lars Are; Karlsbakk, Egil (March 2002). "Metazoan parasites of Maurolicus muelleri (Gmelin) (Sternoptychidae) in Herdlefjorden, western Norway". Sarsia. 87 (1): 47–54. doi:10.1080/003648202753631721. ISSN 0036-4827.
  21. ↑ Klimpel, Sven; Kellermanns, Esra; Palm, Harry W.; Moravec, František (2007-05-30). "Zoogeography of fish parasites of the pearlside (Maurolicus muelleri), with genetic evidence of Anisakis simplex (s.s.) from the Mid-Atlantic Ridge". Marine Biology. 152 (3): 725–732. doi:10.1007/s00227-007-0727-8. ISSN 0025-3162.
  22. 1 2 3 4 5 6 Clarke, Thomas A (1982). Distribution, Growth, and Reproduction of the Lightfish Maurolicus muelleri (Sternoptychidae) off South-East Australia (PDF) (Report). CSIRO Marine Laboratories Reports. ISBN 0-643-02764-5. Report 145.
  23. 1 2 3 4 Staby, A; Røstad, A; Kaartvedt, S (2011-11-15). "Long-term acoustical observations of the mesopelagic fish Maurolicus muelleri reveal novel and varied vertical migration patterns". Marine Ecology Progress Series. 441: 241–255. doi:10.3354/meps09363. hdl:10754/555768. ISSN 0171-8630.
  24. 1 2 3 Christiansen, Svenja; Klevjer, Thor A; Røstad, Anders; Aksnes, Dag L; Kaartvedt, Stein (2021-09-07). Proud, Roland (ed.). "Flexible behaviour in a mesopelagic fish ( Maurolicus muelleri )". ICES Journal of Marine Science. 78 (5): 1623–1635. doi:10.1093/icesjms/fsab075. hdl:10754/668858. ISSN 1054-3139.
  25. ↑ Armstrong, M. J.; Prosch, R. M. (June 1991). "Abundance and distribution of the mesopelagic fish Maurolicus muelleri in the southern Benguela system". South African Journal of Marine Science. 10 (1): 13–28. doi:10.2989/02577619109504615. ISSN 0257-7615.
  26. ↑ Kaartvedt, S; Knutsen, T; Holst, JC (1998). "Schooling of the vertically migrating mesopelagic fish Maurolicus muelleri in light summer nights". Marine Ecology Progress Series. 170: 287–290. doi:10.3354/meps170287. hdl:11250/108326. ISSN 0171-8630.
  27. 1 2 Prosch, R. M. (June 1991). "Reproductive biology and spawning of the myctophid Lampanyctodes hectoris and the sternoptychid Maurolicus muelleri in the southern Benguela Ecosystem". South African Journal of Marine Science. 10 (1): 241–252. doi:10.2989/02577619109504635. ISSN 0257-7615.
  28. ↑ Gjøsæter, Jakob (1981). "Life history and ecology of Maurolicus muelleri (Gonostomatidae) in Norwegian waters". FiskDir. Skr. Ser. HauUnders. 17: 109–131.
  29. ↑ Folkvord, Arild; Gundersen, Geir; Albretsen, Jon; Asplin, Lars; Kaartvedt, Stein; Giske, Jarl (February 2016). Marshall, C. Tara (ed.). "Impact of hatch date on early life growth and survival of Mueller's pearlside ( Maurolicus muelleri ) larvae and life-history consequences". Canadian Journal of Fisheries and Aquatic Sciences. 73 (2): 163–176. doi:10.1139/cjfas-2015-0040. hdl:1956/13128. ISSN 0706-652X.
  30. ↑ Lopes, Plàcida do Carmo (1979). "Eggs and larvae of Maurolicus muelleri (Gonostomatidae) and other fish eggs and larvae from two fjords in western Norway". Sarsia. 64 (3): 199–210. doi:10.1080/00364827.1979.10411382. ISSN 0036-4827.
  31. ↑ Standal, Dag; Grimaldo, Eduardo (2020-09-01). "Institutional nuts and bolts for a mesopelagic fishery in Norway". Marine Policy. 119: 104043. doi:10.1016/j.marpol.2020.104043. ISSN 0308-597X.
  32. ↑ Eduardo Grimaldo; Leif Grimsmo; Paula Alvarez; Bent Herrmann; Guro Møen Tveit; Rachel Tiller; Rasa Slizyte; Naroa Aldanondo; Trude Guldberg; Bendik Toldnes; Ana Carvajal; Marte Schei; Merethe Selnes (December 2020). "Investigating the potential for a commercial fishery in the Northeast Atlantic utilizing mesopelagic species". ICES Journal of Marine Science. 77 (7–8): 2541–2556. doi:10.1093/icesjms/fsaa114. hdl:11250/2685454.
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