Champsocephalus gunnari Lönnberg, 1905

Submitted by KyleeJane 26 Jan
Scientific name:  Champsocephalus gunnari Lönnberg, 1905
Behaviour
Behaviour: 

Mackerel icefish generally become less active and more benthic as they age. Larvae and juveniles are pelagic, active predators of krill. There is some evidence they become more sedentary as they age.

There is no evidence of nesting or guarding a nest in C. gunnari. They reproduce by spawning during 2-3 months of the fall, directly before which they move inshore. (Kock 2005a)

Conservation status
Conservation Status: 

C. gunnari are currently at reduced population levels, but are actively being protected through limitations on catching areas and sizes. The current icefish mackerel fishery has been certified by the international Marine Stewardship Council as sustainable and well managed. (MCS 2012)

Diagnostic description
Diagnostic Description: 

Icefish Mackerel are around 25 -35 cm on average. They're predominantly striped different shades of silver. It appears exceedingly similar to Champhsocephalus exos, its sister species, with a slightly less dorsal-ventrally compressed snout, thicker stripes, and a more southern distribution. (FishBase)

Distribution
Distribution: 

C. gunnari is only found in the Antarctic, most southern region of the world, but is widely distributed south of the Antarctic convergence over shelf areas of sufficiently shallow habitat surrounding sub-Antarctic Islands. Their main area of distribution in the Atlantic Ocean is the Scotia Arc from South Georgia Island in the north to west of the Antarctic Peninsula at approximately 67°S. Their area of distribution in the southern Indian Ocean is around Kerguelen, Heard, and McDonald Islands (Kuhn 2006).

General description
Biology: 

Champsocephalus gunnari Lonnberg, 1905: Preserved specimen
Attribution Share Alike

This fish, along with the other members of the family Channichthyidae, is best known for being the only vertebrates that lack hemoglobin and skeletal myoglobin (Moylan and Sidell 2000). Champhocephalus gunarri is additionally one of only 6 species of fish to lack cardiac myoglobin (Grove et. al 2004). These and other adaptations have made it possible for the mackerel icefish to inhabit successfully the sub-freezing temperatures of the bodies of water surrounding Antarctica. C. gunarri move through different depths of the water column diurnally, from 0 – 800 m, with the oldest specimens staying farther from the surface (Frolkina and Trunov 2004). Using primarily labriform locomotion, flapping their pectoral fins back and forth (Johnston 1989), they feed almost exclusively on krill. 

Habitat
Habitat: 

Mackerel icefish are marine animals. They’re a shallow water, costal fish and live in upper continental shelf regions. Their range of depth is from 0-770 m, with only older adults inhabiting the deeper portions of that range. C. gunnari live in waters -1.86° C to 3 ° C. 6° C is considered the lethal temperature (Kock 2003). 

Morphology
Morphology: 

Champsocephalus gunnari Lönnberg, 1905
Attribution Non‐commercial

C. gunnari have large heads, with depressed, elongate snouts. Their mouth is large with small teeth, all designed to capture their prey of krill and other plankton forms. They are fusiform in shape, tapered at the head and tail, with rounded pelvic fins (Kock 2005a). in C. gunnari and species of the genus  Chionodraco, sexually mature males have a significantly higherfirst dorsal fin than females (Iwami and Kock 1990). Due in part to their lack of hemoglobin, mackerel icefish are predominantly blue and silver hues, with clear, almost white gills.

 

The oxygen carrying capacity of icefish blood is only 10% of what it would be for a fish with hemoglobin (Wojcik 2007). Blood is transparent and less viscous. C. gunnari has several adaptations to compensate for lacking hemoglobin. Its heart is significantly larger than its close relatives who have retained hemoglobin. This enables mackerel icefish to circulate blood volumes of blood 2-4 times greater than fish with hemoglobin (Wojcik 2007). The cold water temperature and thus relatively high concentration of oxygen and relatively low metabolic rates of C. gunnari also help compensating for lack of hemoglobin.   

Because mackerel icefish have increased vascularitzation (higher number and density of veins and arteries) of their fins and scaleless skin it has been suggested that they utilize cutaneous respiration (Feller and Gerday 1997), obtaining oxygen through their skin, though this hasn’t been demonstrated through observation or experimentation.   

Movement and dispersal
Dispersal: 

Due to their spawning, the eggs of C. gunnari are present in the water column and it has been thought that the fish could be distributed and dispersed in this manner, yet the genetic differences of populations suggest there isn't, in reality, much dispersal of fish from their primary habitat. (Kock 2005a). 

Migration: 

Within each upper shelf habitat that supports a C. gunnari population, there appear to be migrations throughout development. Most juveniles (<15 cm) were found in the southern and eastern part of the shelf, or otherwise inshore regions. As fish grow older, they moved to the north of the shelf. Only the oldest fish were observed in the deepest, which corresponded to the most north, sections of the shelf. (Kock 2005a)

While it is still possible that migrations between shelf habitats of the mackerel icefish exist, there has been no report of the in pelagic waters beyond any of the shelf breaks. Also, clear genetic differences have been observed, even between three populations close enough to migrate, making migrations of C. gunnari less likely. (Kuhn 2006)

Physical description
Growth: 

Larvae hatch around 17 to 20 mm then grow at a rate of 0.08 to 0.35 mm daily. C. gunnari, for example, grows about 10 mm per month (Alekseeva and Alekseev 1997). They continue relatively rapid growth of 6-10 cm a year until they reach sexual maturity around 3 years of age. After that they continue growing at a rate of around 5 - 7 cm a year (Kock 2005a). 

Size: 

Maximum size for a C.gannari is 65 cm, though fish this large are rarely reported (review). Most adult fish range 25-35 cm, with the following size guidelines established that juveniles  ranged from 1-15 cm, immature fish from 15-25 cm, mature fish from 25-39 cm, and large mature fish were those greater that 40 cm (Frolkina 2001).

Reproduction and life history
Life expectancy: 

Age estimations have varied greatly for C. gunnari, with variation among populations common as well. A life expectancy of 5-6 years of age has been suggested for populations on northern grounds due to physiological constraints. Other estimates, from South Georgia indicate most fish don’t live past 6 to 7 years. Bouvetoya and the southern Scotia Arc sustain the oldest fish that reach at least 12 to 15 years of age (Kock and Everson 2003).

Reproduction: 

Mackerel icefish become sexually mature at 3 years of age, with the exception of the southern Scotia Arc where they don’t reach maturity till a year later. Upon sexual maturity, they spawn for 2-3 months yearly. Some populations begin to spawn as early as late February and others do not finish their spawning until as late as September. This variation is the result of the different locations of each population and natural variation from year to year (review article). Feeding conditions serve as a trigger for what proportion of a population spawn each year. Kock (1990) estimated that 10–20% of theadult fish do not spawn each year. This proportion may increase to 60% in those years when krill is scarce atSouth Georgia and the fish suffer from malnutrition. Generally, they greatly reduce feeding directly before spawning. They also move closer to shore before spawning to preferred grounds, with males starting this mild migration about a month before females (Everson et al. 2001). C. gunnari have absolute fecundity typically around 2 – 8,000 eggs with a relative fecundity usually in the order of 5-20. Differences between years have been observed in relative fecundity. These differences may be related to the actual condition of the fish (Alekseeva and Alekseev 1997) which may vary considerably between years and even within a season (Everson and Kock 2001). Relative fecundity sometimes decreased with increasing length and weight of the females, such as in C. gunnari (Alekseeva and Alekseev 1997). Eggs of C. gunnari range from 2.6 to 4.1 mm in diameter (Kock 1981) and are demersal, or exist at the sea floor (Everson et al. 2001). Incubation after fertilization takes approximately 3 months, wich is short in comparison to the other icefish (Duhamel 1995). The hatching larvae are 13-17mm in size (Duhamel 1995). Time of hatching varies by location, and appears to happen for several months (North 1990; Everson et al. 2000a). After hatching, they live as active, pelagic predators of krill, becoming increasingly sedentary with age (Kock 2001). 

Trends and threats
Threats: 

Fishing has been regulated and thus currently constitutes only a minor threat to mackerel icefish populations. Other threats however have prevented stocks from returning to pre-exploitation levels. Increased predation, especially by Antarctic fur seals, in response to declines in other prey and krill threatens C. gunnari  populations and inhibits their recovery. Also, inability to deal with climactic changes has been suggested as other threat (Kock 2001). 

Trends: 

From the early 1970s to beginning of the1990s mackerel icefish made up the largest commercial fish catches of any species for large sections of its distribution in response to earlier depletion of Notothenia rossi populations. Catches before regulation of well over 50,000 tons were common (Kuhn 2006). Currently commercial fishing of C. gunnari  is only permitted on a limited scale for the populations of South Georgia, Heard Island, and McDonald Island where populations have recovered in some degree from unregulated exploitation. C. gunnari stocks in the entire Scotia Arc remain at least one order of magnitude larger in the mid-1970 when fisheries were established (Kock 2005b) and fishing there has been prohibited sine 1990 (Kuhn 2006). 

Trophic strategy
Trophic strategy: 

Mackerel icefish are an important part of Antarctic ecosystems. They primarily consume krill, mysids, and hyperiids (small crustaceans), very occasionally eating small fish. In turn, they are eaten by several species of fish. Also, Ade´ lie and chinstrap penguins feed on them at a low rate. Occasionally, arctic fur seals or gentoo penguins will eat mackerel icefish as well. Lastly, humans fish and consume C. gunnari as well. (Kock 2005b)

Uses
Uses: 

Mackerel Icefish are exploited as a source of food and consumed by people. 

References
References: 
Alekseeva, E.L., Alekseev, F.E. (1997). Reproductive biology of mackerel icefish, Champsocephalus gunnari, from the region of South Georgia and Shag Rocks. Vopr Ikthiol. 37(3), 385–392. Transl as J Ichthyol. 37(4), 304–311.
Feller G, Gerday C (1997) Adaptations of the haemoglobinless Antarctic icefish (Channichthyidae) to hypoxia tolerance. Comp Biochem Physiol. 118A, 981–987.
FishBase. "Champsocephalus Gunnari Lönnberg, 1905 Mackerel Icefish." 08 May 2012. <http://www.fishbase.org/Summary/SpeciesSummary.php?id=474#>.
Frolkina, Z.A., (2001) Age length composition of mackerel icefishfrom the South Georgia shelf. CCAMLR Sci. 8, 133–146.
Grove, T.J., Hendrickson, J.W., Sidell B.D. (2004) Two species of Antarctic icefishes (genus Champsocephalus) share a common genetic lesion leading to the loss of myoglobin expression. Polar Biol. 27, 579–585.
Kock KH, Everson I (2003). Shedding new light on the life cycle of mackerel icefish in the Southern Ocean. J Fish Biol. 63, 1–21.
Kock K-H (2005a) Antarctic icefishes (Channichthyidae: a unique family of fishes). A review, Part I. Polar Biol. 28,862–895.
Kock K-H (2005b) Antarctic icefishes (Channichthyidae: a unique family of fishes). A review, Part II. Polar Biol. 28,897–909.
Kuhn, K. L., and Gaffney, P.M. (2006). Preliminary assessment of population structure in the mackerel icefish(Champsocephalus gunnari). Polar Biol. 29, 927–935.
"Mackerel Icefish — MSC." Marine Stewardship Council - Home — MSC. Web. 08 May 2010. <http://www.msc.org/cook-eat-enjoy/fish-to-eat/mackerel-icefish>.
Moylan, T.J., Sidell, B.D., (2000) Concentrations of myoglobin mRNA in heart ventricle from Antarctic fishes. J Exp Biol. 203, 1277–1286.
Wujcik, J.M., Wang, G., Eastman, J.T., and Sidell, B. D. (2007) Morphometry of retinal vasculature in Antarctic fishes is dependent upon the level of hemoglobin in circulation. J Exp Biol. 210, 815-824.
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