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