Chaenocephalus aceratus

Last updated

Chaenocephalus aceratus
Chaenocephalus aceratus.jpg
Not evaluated (IUCN 3.1)
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Actinopterygii
Order:
Perciformes
Suborder:
Notothenioidei
Family:
Channichthyidae
Genus:
Chaenocephalus

Regan, 1913
Species:
C. aceratus
Binomial name
Chaenocephalus aceratus
(Lönnberg, 1906)

Chaenocephalus aceratus, commonly known as the blackfin icefish or the Scotia Sea icefish, is a species of crocodile icefish belonging to the family Channichthyidae. [1] The blackfin icefish belongs to Notothenioidei, a suborder of fishes that accounts for 90% of the fish fauna on the Antarctic continental shelf. [2] Icefishes, also called white-blooded fishes, are a unique family in that they are the only known vertebrates to lack haemoglobin, making their blood oxygen carrying capacity just 10% that of other teleosts. [3] Icefishes have translucent blood and creamy white gills. [4]

Contents

Morphology

The blackfin icefish has an elongated, tapered body with a relatively weakly ossified skeleton. [5] It lacks scales and has thin, highly vascularised skin. Its body structure makes it extremely vulnerable to injury. [5] Its head and snout are depressed with a single nostril on either side of the head, and a large mouth with small teeth. [5]

This species can range from grey to brown in colour and can have dark vertical stripes along its side. [5] It has two dorsal fins and thickened skin on the pelvic fins, which is thought to be an adaptation to allow the fish to rest on the ocean substrate, as it lacks a swim bladder to maintain buoyancy. [6] This species is sexually dimorphic, with the males having longer and darker first dorsal fins than females. [7] At sexual maturation, females (48–49 cm) are significantly larger than males (34–40 cm), and spawning females are larger than non-spawning females. [7]

Habitat

The blackfin icefish is known to reside in the Southern Ocean around Antarctica. [8] Most research on the blackfin icefish has been carried out around the Scotia Arc, encompassing South Georgia, the South Shetland Islands, Bouvet Island, the South Orkney Islands, and the Antarctic Peninsula. [8]

The ocean temperature in these regions usually remains within a few degrees of the freezing point of seawater, -2 °C (28 °F). [9] Consequently, the blackfin icefish is a stenothermal ectotherm, meaning it has a narrow thermal tolerance range and a low upper thermal limit. [10] The Southern Ocean has a high oxygen content, which allows the blackfin icefish to survive without haemoglobin. [11]

Blackfin icefish are typically found at depths of 0-770 m, depending on their life stage. Larvae and juveniles tend to be more active in the water column but are typically found closer to the shore, while adults more often exhibit benthic swimming behaviour. [12]

Evolution

There are at least 16 known species of icefish, and they are thought to make up a monophyletic group. [13] The icefishes likely descended from a sluggish demersal ancestor. [4] During the mid-Tertiary period, a species crash in the Southern Ocean opened up a wide range of empty niches to colonize. Despite the hemoglobin-less mutants being less fit, the lack of competition allowed even the mutants to leave descendants that colonized empty habitats and evolved compensations for their mutations. Later, the periodic openings of fjords created habitats that were colonized by a few individuals. These conditions may have also allowed for the loss of myoglobin.

It is still unknown when the icefish evolved, but there are two main competing hypotheses. The first is that they are only about 6 million years old, appearing after the Southern Ocean cooled significantly. The second predicts that they are much older, evolving 15-20 million years ago. [4] Although the evolution of icefish is still disputed, it is widely accepted that the formation of the Antarctic Polar Frontal Zone (APFZ) and the Antarctic Circumpolar Current (ACC) marks the beginning of the evolution of Antarctic fishes. [2] The ACC is an oceanic current that moves in a clockwise northeast direction, and can be up to 10,000 km wide. This current formed 25-22 million years ago, and thermally isolated the Southern Ocean by separating it from the warm subtropical gyres to the north. [2]

The various lifestyles of icefish are thought to have caused speciation within the family. For example, blackfin icefish adults have a very sedentary lifestyle, which may have geographically isolated them from other members of the family. Other species, such as Champsocephalus gunnari , are more pelagic and seem to have avoided isolation. [14]

Adaptation

The Southern Ocean is one of the most extreme habitats on the planet. Like most other Antarctic notothenioids, the blackfin icefish produces antifreeze glycoproteins in their blood and other body fluids. [15] These proteins reduce the internal freezing temperature, preventing ice crystallization and thus allowing the fish to survive in water below 0 °C.

In addition, icesfishes have developed a specialized cardiovascular system to compensate for the lack of hemoglobin and maximize oxygen delivery to tissues. [16] Because icefish blood lacks erythrocytes, it is less viscous and can flow more easily around the body at low temperatures. [17] As a result, the amount of energy expended to transport oxygen is reduced. [18]

Icefish also possess an enlarged, hypertrophied heart, which allows the animal to pump very large volumes of blood at a low pressure and speed. The stroke volume of the icefish heart is 6-15 times that of other teleosts, and the blood volume in general is 2-4 times as large as other teleosts. [19] The blackfin icefish also maintains very high concentrations of mitochondria in its cardiac muscle cells [20] and thin, highly vascularized skin. [16] All of these adaptations allow the blackfin icefish to maximize oxygen delivery and survive without haemoglobin. [16]

Diet

Blackfin icefish primarily eat smaller fish and krill, but have occasionally been found with crustaceans in their stomachs. [21] Younger icefish tend to eat krill, and then switch to mackerel icefish when they grow (about 30 cm). From data collected in different locations, researchers have determined that the blackfin icefish likely feeds sporadically, consuming large quantities of fish and krill at a time, but at irregular intervals. [22] Their lack of haemoglobin supports this behaviour because burst activity would allow them to obtain energy anaerobically, reducing the need for oxygen. While larvae and juveniles are more active in the water column searching for krill, the adult blackfin icefish usually works as an ambush predator, sitting on the substrate until prey swim past. [23]

Reproduction

The blackfin icefish takes between 5 and 7 years to reach reproductive age, and it expends a large amount of energy when it comes to reproducing and parenting. Females typically spawn large, slow-developing embryos that are up to 5 mm in diameter. [24] However, the large yolky eggs mean that females rarely produce over 10,000 eggs per spawning. [25] Males dig shallow, circular depressions on the seafloor and clear the surrounding area of debris for a female to spawn her eggs. The embryos are at high risk of predation because they are demersal, so males spend the months between spawning and hatching ferociously guarding the eggs. This also makes males particularly vulnerable to being caught as trawling bycatch. [24]

Spawning appears to follow a latitudinal trend, with spawning primarily taking place between autumn and winter, but progressively later in the southernmost populations. [26] During spawning season, blackfin icefish tend to migrate closer to shore. Female blackfin icefish are total spawners with determinate fecundity, and typically spawn every year. [26] However, because reproduction requires large amounts of energy and icefish are limited due metabolically to lack of haemoglobin, sexually mature females may skip a season of spawning if food has been scarce or of poor quality. [26] The incubation period can take 2 to 6 months to complete, depending on the latitude (more southerly regions have longer incubation periods). The larvae remain pelagic for 5 to 7 years until maturity, growing relatively quickly at about 6 to 10 cm each year. [27]

Threats

Although blackfin icefish is not caught commercially, it is often caught as bycatch when fishermen trawl for mackerel icefish. [5] Even if the blackfin icefish is thrown back after being caught, it has a high mortality rate due to its fragile structure and vulnerability to stress. Additionally, its benthic behaviour makes it more vulnerable to being caught in trawling nets. [5] Researchers are currently working to understand how marine protected areas can be created for this species, and the best ways to handle them to reduce stress and injury. [28]

Another major threat facing the blackfin icefish is climate change. The blackfin icefish can only survive within a very narrow temperature range. [10] This is due in part to the high dissolved oxygen content of ice-cold seawater, which it requires due to lack of haemoglobin. Rising sea temperatures pose a serious threat to this species, and scientists are studying blackfin icefish physiology to see how severely climate change will affect this species, particularly at embryonic and larval stages. [29] [30]

Related Research Articles

Nototheniidae

The notothens or cod icefishes are the family Nototheniidae of acanthopterygian fishes. They are traditionally placed in the order Perciformes together with their relatives, but like every lineage in the order, actual phylogenetic relationships among these species have not yet been determined with certainty.

Channichthyidae Family of fishes

The crocodile icefish or white-blooded fish (Channichthyidae) comprise a family of notothenioid fishes found in the Southern Ocean around Antarctica. They are the only known vertebrates to lack hemoglobin in their blood as adults. Icefish populations are known to reside in the Atlantic and Indian sectors of the Southern Ocean as well as the continental shelf waters surrounding Antarctica. Water temperatures in these regions remain relatively stable, generally ranging from −1.8 to 2 °C. One icefish, Champsocephalus esox, is distributed north of the Antarctic Polar Frontal Zone. At least sixteen species of crocodile icefish are currently recognized, although eight additional species have been proposed for the icefish genus Channichthys.

Antarctic fur seal

The Antarctic fur seal, is one of eight seals in the genus Arctocephalus, and one of nine fur seals in the subfamily Arctocephalinae. Despite what its name suggests, the Antarctic fur seal is mostly distributed in Subantarctic islands and its scientific name is thought to have come from the German vessel SMS Gazelle, which was the first to collect specimens of this species from Kerguelen Islands.

<i>Gromia</i> Genus of protists

Gromia is a genus of protists, closely related to foraminifera, which inhabit marine and freshwater environments. Gromia are ameboid, producing filose pseudopodia that extend out from the cell’s proteinaceous test through a gap enclosed by the cell’s oral capsule. The test, a shell made up of protein that encloses the cytoplasm, is made up of several layers of membrane, which resemble honeycombs in shape — a defining character of this genus.

Icefishes or noodlefishes are a family, the Salangidae, of small osmeriform fish, related to the smelts. They are found in Eastern Asia, ranging from the Russian Far East in the north to Vietnam in the south, with the highest species richness in China. Some species are widespread and common, but others have relatively small ranges and are threatened. Depending on species, they inhabit coastal marine, brackish or fresh water habitats, and some are anadromous, only visiting fresh water to spawn.

Antarctic silverfish Species of fish

The Antarctic silverfish is a species of notothen native to the Southern Ocean and the only truly pelagic fish in the waters near Antarctica. It is a keystone species in the ecosystem of the Southern Ocean.

Notothenioidei

Notothenioidei is one of 19 suborders from the order Perciformes and that primarily includes Antarctic fish and Subantarctic fish, but also a few species ranging north to southern Australia and southern South America. These species, which are referred to collectively as the notothenioids, account for approximately 90% of the fish fauna biomass in the continental shelf waters surrounding Antarctica.

Neosalanx tangkahkeii, the Chinese icefish or short-snout icefish, is a species of icefish endemic to fresh and brackish waters in China. Despite its common name it is not the only icefish in China; the majority of the species in this family are found in the country.

<i>Adamussium</i>

Adamussium is a monotypic genus of bivalve molluscs in the large family of scallops, the Pectinidae. The Antarctic scallop is the only species in the genus though its exact relationship to other members of the family is unclear. It is found in the ice-cold seas surrounding Antarctica, sometimes at great depths.

<i>Galiteuthis glacialis</i>

Galiteuthis glacialis is a species of glass squid from the Antarctic Convergence. It is in the cranchiidae family and subfamily taoniinae. They are endemic to the Antarctic and are found in the Southern Ocean, around the Weddell Sea and South Shetland Islands. Galiteuthis glacialis are one of the most plentiful and widely dispersed species of Antarctic squid. These squids are found in the mesopelagic and bathypelagic layers of the open ocean and demonstrate vertical migration. They can reach a maximum mantle length of 500 mm (0.5m).

<i>Chionodraco</i>

Chionodraco is a genus of crocodile icefishes found in the Southern Ocean.

<i>Neopagetopsis ionah</i>

Neopagetopsis ionah, Jonah's icefish, is a benthopelagic species of crocodile icefish found in the Southern Ocean at depths of from 20 to 900 metres. It has a circum-Antarctic distribution on the continental slope and continental shelf, with the northernmost records from the South Shetland and the South Orkney Islands.

<i>Chionodraco rastrospinosus</i>

The ocellated icefish is a fish of the family Channichthyidae. It lives in the cold waters off Antarctica and is known for having transparent haemoglobin-free blood.

Wildlife of Antarctica

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Antarctic fishes

Antarctic fish is a common name for a variety of fish that inhabit the Southern Ocean. There are relatively few families in this region, the most species rich-being the Liparidae (snailfishes), followed by Nototheniidae. The latter is one of five different families that belong to the suborder Notothenioidei of the order Perciformes. The other four are Artedidraconidae, Bathydraconidae, Channichthyidae and Harpagiferidae. They are also called notothenioids, but this name is also used to describe the other three, non-Antarctic families and some of the non-Antarctic genera in the mainly Antarctic families belonging to the suborder.

<i>Notothenia coriiceps</i>

Notothenia coriiceps, also known as the black rockcod, Antarctic yellowbelly rockcod, or Antarctic bullhead notothen, is a species of notothen that is widely spread around the Antarctic continent. Like other Antarctic notothenioid fishes, N. coriiceps evolved in the stable, ice-cold environment of the Southern Ocean. It is not currently targeted by commercial fisheries.

Neolithodes capensis is a species of king crab which is found in the Southern Ocean and the western Indian Ocean. It has been found to a depth of 660–3,200 metres (2,170–10,500 ft).

Neolithodes diomedeae is a species of king crab which is found in the eastern Pacific Ocean, the southwestern Atlantic Ocean, and the Bellingshausen and Scotia Seas in the Southern Ocean.

<i>Channichthys rhinoceratus</i>

Channichthys rhinoceratus, the unicorn icefish, is a species of crocodile icefish found only around the Kerguelen-Heard Plateau in the Southern Ocean. It is a demersal species living from surface waters to depths up to 750 m (2,460 ft). It is considered by some researchers as the only species in the genus Channichthys.

Channichthys panticapaei, the charcoal icefish, is a species of crocodile icefish endemic to the Kerguelen Islands area in the Southern Ocean. This demersal species is found at depths of 112–154 m (367–505 ft) and is sometimes caught in bottom trawls. It is dark gray to uniformly blackish with long first to third dorsal fin spines. The charcoal icefish reaches lengths of up to 40.2 cm (15.8 in), with males generally being larger. This planktivorous (plankton-eating) species likely spawns from June to July.

References

  1. ↑ "Species Chaenocephalus aceratus Lönnberg 1906". FishWisePro. 1906. Retrieved 18 April 2020.
  2. 1 2 3 Eastman, Joseph (1993). Antarctic Fish Biology: Evolution in a Unique Environment. San Diego, California: Academic Press, Inc.
  3. ↑ Holeton, George (30 September 1969). "Oxygen Uptake and Circulation by a Hemoglobinless Antarctic Fish (Chaenocephalus aceratus Lonnberg) Compared With Three Red-Blooded Antarctic Fish". Comp. Biochem. Physiol. 34 (2): 457–471. doi:10.1016/0010-406X(70)90185-4. PMID   5426570.[ permanent dead link ]
  4. 1 2 3 Kock, Karl (9 August 2005). "Antarctic icefishes (Channichthyidae): a unique family of fishes. A review, Part I". Polar Biology. 28 (11): 862–895. doi:10.1007/s00300-005-0019-z. S2CID   12382710.
  5. 1 2 3 4 5 6 Le Francois, Nathalie; Sheehan, Eileen; Desvignes, Thomas; Belzile, Claude; Postelthwait, John; Dietrich II, William (12 July 2017). "Characterization and husbandry of wild broodstock of the blackfin icefish Chaenocephalus aceratus (Lönnberg 1906) from the Palmer Archipelago (Southern Ocean) for breeding purposes". Polar Biology. 40 (12): 2499–2516. doi:10.1007/s00300-017-2161-9. S2CID   27157380.
  6. ↑ Kock, Karl (9 August 2005). "Antarctic icefishes (Channichthyidae): a unique family of fishes. A review, Part I". Polar Biology. 28 (11): 862–895. doi:10.1007/s00300-005-0019-z. S2CID   12382710.
  7. 1 2 Dietrich III, William; Jones, Christopher; Kim, Stacy; North, Anthony; Thurber, Andrew; Vacchi, Marino (29 July 2005). "Nesting behavior of the icefish Chaenocephalus aceratus at Bouvetøya Island, Southern Ocean". Polar Biology. 28 (11): 828–832. doi:10.1007/s00300-005-0010-8. S2CID   38630559.
  8. 1 2 Reid, W; Clarke, S; Collins, M; Belchier, M (2007). "Distribution and ecology of Chaenocephalus aceratus (Channichthyidae) around South Georgia and Shag Rocks (Southern Ocean)".Cite journal requires |journal= (help)
  9. ↑ Surface Temperature - NOAA's Science On a Sphere". National Oceanic and Atmospheric Administration. 2018.
  10. 1 2 Beers, J.M. and Sidell, B.D. (2011). "Thermal Tolerance of Antarctic Notothenioid Fishes Correlates with Level of Circulating Hemoglobin" (PDF). Physiological and Biochemical Zoology. 84 (4): 353–362. doi:10.1086/660191. PMID   21743249. S2CID   30043314.CS1 maint: multiple names: authors list (link)
  11. ↑ Clarke, A (1990). "Temperature and evolution: Southern Ocean cooling and the Antarctic marine fauna". Antarctic Ecosystems: 9–22. doi:10.1007/978-3-642-84074-6.
  12. ↑ Reid, W; Clarke, S; Collins, M; Belchier, M (2007). "Distribution and ecology of Chaenocephalus aceratus (Channichthyidae) around South Georgia and Shag Rocks (Southern Ocean)".Cite journal requires |journal= (help)
  13. ↑ Kock, Karl (9 August 2005). "Antarctic icefishes (Channichthyidae): a unique family of fishes. A review, Part I". Polar Biology. 28 (11): 862–895. doi:10.1007/s00300-005-0019-z. S2CID   12382710.
  14. ↑ Kock, Karl (9 August 2005). "Antarctic icefishes (Channichthyidae): a unique family of fishes. A review, Part I". Polar Biology. 28 (11): 862–895. doi:10.1007/s00300-005-0019-z. S2CID   12382710.
  15. ↑ Chen, L; et al. (1997). "Evolution of antifreeze glycoprotein gene from a trypsinogen gene in Antarctic notothenioid fish". PNAS. 94: 3811–3816.
  16. 1 2 3 Sidell, Bruce D; Kristin M O'Brien (2006-05-15). "When Bad Things Happen to Good Fish: The Loss of Hemoglobin and Myoglobin Expression in Antarctic Icefishes". Journal of Experimental Biology. 209 (10): 1791–1802. doi:10.1242/jeb.02091. ISSN 0022-0949. PMID 16651546.
  17. ↑ Sidell, Bruce D; Kristin M O'Brien (2006-05-15). "When Bad Things Happen to Good Fish: The Loss of Hemoglobin and Myoglobin Expression in Antarctic Icefishes". Journal of Experimental Biology. 209 (10): 1791–1802. doi:10.1242/jeb.02091. ISSN 0022-0949. PMID 16651546. Retrieved 2012-04-07.
  18. ↑ Joyce, W; et al. (2019). "Adrenergic and Adenosinergic Regulation of the Cardiovascular System in an Antarctic Icefish: Insight into Central and Peripheral Determinants of Cardiac Output" (PDF). Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 230: 28–38. doi:10.1016/j.cbpa.2018.12.012.
  19. ↑ Kock, Karl (9 August 2005). "Antarctic icefishes (Channichthyidae): a unique family of fishes. A review, Part I". Polar Biology. 28 (11): 862–895. doi:10.1007/s00300-005-0019-z. S2CID   12382710.
  20. ↑ Urschel, M.R. and O'Brien, K.M. (2008). "High mitochondrial densities in the hearts of Antarctic icefishes are maintained by an increase in mitochondrial size rather than mitochondrial biogenesis". Journal of Experimental Biology. 211 (Pt 16): 2638–2646. doi: 10.1242/jeb.018598 . PMID   18689417.CS1 maint: multiple names: authors list (link)
  21. ↑ Dietrich III, William; Jones, Christopher; Kim, Stacy; North, Anthony; Thurber, Andrew; Vacchi, Marino (29 July 2005). "Nesting behavior of the icefish Chaenocephalus aceratus at Bouvetøya Island, Southern Ocean". Polar Biology. 28 (11): 828–832. doi:10.1007/s00300-005-0010-8. S2CID   38630559.
  22. ↑ Le Francois, Nathalie; Sheehan, Eileen; Desvignes, Thomas; Belzile, Claude; Postelthwait, John; Dietrich II, William (12 July 2017). "Characterization and husbandry of wild broodstock of the blackfin icefish Chaenocephalus aceratus (Lönnberg 1906) from the Palmer Archipelago (Southern Ocean) for breeding purposes". Polar Biology. 40 (12): 2499–2516. doi:10.1007/s00300-017-2161-9. S2CID   27157380.
  23. ↑ Kock, Karl (9 August 2005). "Antarctic icefishes (Channichthyidae): a unique family of fishes. A review, Part I". Polar Biology. 28 (11): 862–895. doi:10.1007/s00300-005-0019-z. S2CID   12382710.
  24. 1 2 Militelli, M; Macchi, G; Rodrigues, K (11 April 2015). "Maturity and fecundity of Champsocephalus gunnari, Chaenocephalus aceratus and Pseudochaenichthys georgianus in South Georgia and Shag Rocks Islands". Polar Science. 9 (2): 258–266. doi: 10.1016/j.polar.2015.03.004 .
  25. ↑ Kock, Karl (9 August 2005). "Antarctic icefishes (Channichthyidae): a unique family of fishes. A review, Part I". Polar Biology. 28 (11): 862–895. doi:10.1007/s00300-005-0019-z. S2CID   12382710.
  26. 1 2 3 Militelli, M; Macchi, G; Rodrigues, K (11 April 2015). "Maturity and fecundity of Champsocephalus gunnari, Chaenocephalus aceratus and Pseudochaenichthys georgianus in South Georgia and Shag Rocks Islands". Polar Science. 9 (2): 258–266. doi: 10.1016/j.polar.2015.03.004 .
  27. ↑ Kock, Karl (9 August 2005). "Antarctic icefishes (Channichthyidae): a unique family of fishes. A review, Part I". Polar Biology. 28 (11): 862–895. doi:10.1007/s00300-005-0019-z. S2CID   12382710.
  28. ↑ Le Francois, Nathalie; Sheehan, Eileen; Desvignes, Thomas; Belzile, Claude; Postelthwait, John; Dietrich II, William (12 July 2017). "Characterization and husbandry of wild broodstock of the blackfin icefish Chaenocephalus aceratus (Lönnberg 1906) from the Palmer Archipelago (Southern Ocean) for breeding purposes". Polar Biology. 40 (12): 2499–2516. doi:10.1007/s00300-017-2161-9. S2CID   27157380.
  29. ↑ Le Francois, Nathalie; Sheehan, Eileen; Desvignes, Thomas; Belzile, Claude; Postelthwait, John; Dietrich II, William (12 July 2017). "Characterization and husbandry of wild broodstock of the blackfin icefish Chaenocephalus aceratus (Lönnberg 1906) from the Palmer Archipelago (Southern Ocean) for breeding purposes". Polar Biology. 40 (12): 2499–2516. doi:10.1007/s00300-017-2161-9. S2CID   27157380.
  30. ↑ Somero, GN (2009). "The physiology of climate change: how potentials for acclimatization and genetic adaptation will determine 'winners' and 'losers'". Journal of Experimental Biology. 213 (6): 912–920. doi: 10.1242/jeb.037473 . PMID   20190116.
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