Scotia sea icefish
The blackfin icefish (Chaenocephalus aceratus), also known as the Scotia Sea icefish, is a species of crocodile icefish belonging to the family Channichthyidae. The blackfin icefish belongs to Notothenioidei, a suborder of fishes that accounts for 90% of the fish fauna on the Antarctic continental shelf. 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. Icefishes have translucent blood and creamy white gills.
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CarnivoreA carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of a...
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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starts withThe blackfin icefish has an elongated, tapered body with a relatively weakly ossified skeleton. It lacks scales and has thin, highly vascularised skin. Its body structure makes it extremely vulnerable to injury. Its head and snout are depressed with a single nostril on either side of the head, and a large mouth with small teeth.
This species can range from grey to brown in colour and can have dark vertical stripes along its side. 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. This species is sexually dimorphic, with the males having longer and darker first dorsal fins than females. At sexual maturation, females (48–49 cm) are significantly larger than males (34–40 cm), and spawning females are larger than non-spawning females.
The blackfin icefish is known to reside in the Southern Ocean around Antarctica. 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.
The ocean temperature in these regions usually remains within a few degrees of the freezing point of seawater, -2 °C (28 °F). Consequently, the blackfin icefish is a stenothermal ectotherm, meaning it has a narrow thermal tolerance range and a low upper thermal limit. The Southern Ocean has a high oxygen content, which allows the blackfin icefish to survive without haemoglobin.
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.
Blackfin icefish primarily eat smaller fish and krill, but have occasionally been found with crustaceans in their stomachs. 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. 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.
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. However, the large yolky eggs mean that females rarely produce over 10,000 eggs per spawning. 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.
Spawning appears to follow a latitudinal trend, with spawning primarily taking place between autumn and winter, but progressively later in the southernmost populations. 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. 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. 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.
Although blackfin icefish is not caught commercially in direct fisheries, it is often caught as bycatch when fishermen trawl for mackerel icefish, and the flesh is of excellent quality. 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. 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.
Another major threat facing the blackfin icefish is climate change. The blackfin icefish can only survive within a very narrow temperature range. 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.
