Champsocephalus gunnari
FAMILY
Channichthyidae
TAXONOMY
Champsocephalus gunnari Lцnnberg, 1905, Cumberland Bay,
South Georgia.
OTHER COMMON NAMES
English: Crocodile icefish, pike glassfish; French: Poisson des
glaces; Spanish: Draco rayado; Russian: Ledyanaya ryba.
PHYSICAL CHARACTERISTICS
Elongated, scaleless, pikelike body (length/depth ratio, about
7:2) with an elongated snout. The jaws do not protract. In coloring
it is silvery gray, darker on the back, and silvery on the
belly, with dark vertical stipes on the sides, reminiscent of
those seen in mackerel. The gills are a pale yellowish; the
blood is colorless, completely lacking hemoglobin. The absence
of hemoglobin is a remarkable feature of all 15 icefish
species, apparently caused by a single massive mutation that
deleted the _-globin gene. Far from being an adaptation to
Antarctic conditions, this has been termed a “disaptation.” Several
factors have enabled channichthyids to survive this evolutionary
catastrophe: frigid seawater and blood plasma can carry
more dissolved oxygen, and low body temperatures limit metabolic
requirements. Subsequent evolution has compensated for
the loss of an oxygen-binding pigment: blood volume, heart,
vessel, and gill size and the perfusion rate of gills and blood
vessels all have increased. As a consequence, channichthyids are
surprisingly active, competing successfully with other notothenioids.
DISTRIBUTION
South Georgia and the islands of the Scotia Arc, southward to
the northern Antarctic Peninsula; it also inhabits Bouvet, Kerguelen,
and Heard Islands. A closely related species, C. esox,
occurs in the Falklands Islands and Patagonia and is the only
channichthyid to occur outside Antarctic/subantarctic waters.
HABITAT
This is a coastal species, found mainly between 330 and 1,140
ft (100–350 m). Mature adults are found offshore in summer,
moving inshore to spawn in the fall (March–May).
BEHAVIOR
The species aggregates in locations with dense krill populations,
remaining near the bottom during the day and migrating
upward with the krill at night.
FEEDING ECOLOGY AND DIET
The mackerel icefish feeds mainly on krill (Euphausia superba);
it takes other euphausiids, mysids, and hyperiid amphipods
(Themisto gaudichaudii) when krill numbers are low.
REPRODUCTIVE BIOLOGY
Reproductive parameters vary considerably between the different
stocks. Maturation of oocytes takes less than a year, producing
1,300–31,000 eggs that are 0.12–0.16 in (3–4 mm) in diameter.
When krill are scarce, oocytes may be resorbed, and as many as
60% of mature females may be nonreproductive. A marked
three-year periodicity in reproduction is reported from the Kerguelen
stock. Near South Georgia, spawning occurs from March
to May; it takes place later in South Orkney and South Shetland
and as late as July to August in the Kerguelen stock. Eggs are
deposited in the depth range of 330–660 ft (100–200 m) and
hatch after 30–180 days, depending on the stock. Newly hatched
larvae are 0.05–0.07 in (12–17 mm) long and feed on copepods
within 12 mi (20 km) offshore; larger juvenile fish move further
offshore but remain over the continental shelf. Juveniles grow at
2.5–3.5 in (6.4–8.9 cm) per year, reaching sexual maturity at
three years at a length of 10 in (25 cm).
CONSERVATION STATUS
Not listed by the IUCN. The various stocks of mackerel icefish
have been targeted by minor trawl fisheries since 1974.
Catches fluctuate from year to year, but they appear to be sustainable
for the South Georgia and Kerguelen stocks. In South
Orkney and South Shetland, the stock was depleted rapidly below
sustainable levels and is no longer being fished.
SIGNIFICANCE TO HUMANS
A total catch of 4,295 tons (3,896 tonnes) was reported from
the Commission for the Conservation of Antarctic Marine Resources
management area in 1999–2000.
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