Fish of the Day
Today's fish of the day is the Antarctic toothfish!
The Antarctic toothfish, also known as the Chilean sea bass, Antarctic cod,and scientific name Dissostichus mawsoni, is found across Antarctica's southern seas. Mainly the Ross Sea, although they can be found across the seas of the continent. Like many fish in the Antarctic, the Antarctic toothfish is known primarily for their strange ability to produce antifreeze proteins in their blood. This allows these fish free reign to live from 200-3,300 meters below the surface of the water where temperatures can get as low as sub zero, below freezing. Other temperature adaptations include the massive fat deposits in the fish, which they use to control buoyancy, as the Antarctic toothfish has no swim bladder! This works as the adult fish are naturally neutrally buoyant.
Antarctic toothfish fill a very particular role in the ecosystem, that of the mid sized predator in both bottom dwelling and mid water prey, and smaller predators, eating fish and smaller squids. Usually growing to a size of 60cm, with some specimen growing as large as 2 meters in length, and as heavy as 150kg. Their role as a mid sized predator is usually filled by sharks around the world, however these waters are much too cold to support them. Predated by sperm whales, killer whales, seals, and larger fish. These fish are not known for their particular speed, as the fish slowly loses the ability to swim in "sprints" as it ages, but as juveniles they can temporarily reach speeds high enough to escape adult Weddell seals. Despite lacking proper eyesight, the Antarctic toothfish has two lateral line organs that span the body, which are used for low light sensing, this combined with a wonderful sense of smell provides fish their information on the surrounding environment.
The lifecycle of the antarctic toothfish is relatively slow, as sexual maturity isn't achieved until age 13 for females (around 120cm) and 17 for male toothfish (around 133cm long). This is when these fish migrate North from the Ross sea onto the sea mounts of the Pacific Antarctic ridge. The Antarctic toothfish spawns around June-October at a depth of 1000-16000 meters deep, migrating North for 6-18 months, before returning back to the Ross sea. During their time at the breeding mounts, these fish will release their eggs and milt into the Ross Sea Gyre, although it is unknown how often these fish spawn during their time at these sea mounts. These eggs are fertilized by chance, and usually hatch around February-November. Juvenile fish, those who are between 40-80cm long, are found in higher waters, between 750 meters and up, but will quickly move to deeper waters once they're grown. Despite their long lifespan, these fish will reach a third of their total size within 5 years, and two thirds of their total size within 10 years. From there as these fish age they will progressively go to deeper and deeper waters, before passing away at around 50 years of age.
Sources:
Toothfish. Toothfish | Australian Fisheries Management Authority. (n.d.). https://www.afma.gov.au/species/toothfish
Dissostichus Mawsoni summary page. FishBase. (n.d.-a). https://www.fishbase.se/summary/Dissostichus-mawsoni
Toothfish life history. NIWA. (n.d.). https://niwa.co.nz/fisheries/antarctic-fisheries-research/toothfish-life-history
All about Antarctic toothfish. Last Ocean, New Zealand, Antarctica. (n.d.). http://www.lastocean.org/commercial-fishing/about-toothfish/all-about-antarctic-toothfish-__I.2445
