Our first trawl recovered a surprisingly large variety and high number of fishes. This was unlike the trawls conducted in the previous FjordEco expedition and unlike the second trawl of this cruise. Multiple families of fishes were recovered: eelpouts (Zoarcidae), dragonfishes (Bathydraconidae), rockcods (Notothenidae), and icefishes (Channichthyidae).
Eelpouts resemble sock-puppets, which is how they merited their name “eel” “pout”. They are bottom dwellers that often curl their eel-like bodies into sinuous ‘S’ shapes on the seafloor. Their heads are covered in large sensory pores, and they can seem a bit like lizards when they use their round large pectorals to ‘walk’ along the seafloor pushing themselves forward slowly. They are generally not very active fishes, in fact, some individuals were seen in two photos in a row on the time-lapse camera meaning they had remained motionless for at least six hours. Nevertheless, when they are motivated, they can swim slightly off the bottom like eels. The individuals we caught in the trawl were in the genus Ophthalmolycus, identified by a bluish abdomen, visible teeth, and the relatively long length of their reduced pelvic fins. Eelpouts are common fishes inhabiting the Antarctic seafloor, and we recovered many individuals of possibly two different genera.
A fascinating group of Antarctic fishes are the white blooded icefishes (family Channichthyidae). These fishes are the only fish in the world that have no hemoglobin in their blood. This makes their hearts white and their gills nearly translucent. Hemoglobin is the protein that vertebrates use to carry oxygen in their bloodstream from their lungs to their tissues. It is still a bit of a mystery how these fishes can survive and maintain high levels of activity (like that needed to chase down and eat mobile prey like krill and fishes) without an oxygen carrier. The low temperatures of Antarctic water allow for a higher concentration of dissolved gases including oxygen in the water. Sea surface temperature (or SST) has been around -1 degrees C (this is possible because the freezing point of seawater is actually lower than that of fresh water, around -1.9 C). This high concentration of dissolved oxygen along with the icefishes’ thin, highly vascularized skin may allow these fish to get enough oxygen, even without hemoglobin. The amazing physiology of these fishes is still a topic of ongoing research. In the trawl we recovered 5 different species of icefishes.
We also recovered at least two species of rockcods. These fishes are red-blooded, but also have an interesting adaptation that is shared among most polar species: anti-freeze proteins. These proteins prevent ice growth in the blood stream at freezing temperatures. This group of fishes is an extremely diverse group of predators, many of which are very similar and difficult to differentiate.
This trawl was a rare chance to see a large diversity of Antarctic fishes, and with the expert photography of Maria Stenzel, we can share some of this diversity with beautiful, detailed photographs.
Written by Astrid Leitner.
Pagothenia hansoni (rockcod) retrieved from a depth of 480 to 500 meters in the middle basin of Andvord Bay, western Antarctic Peninsula. Antarctic rockcods (family Notothenidae) are the largest and most diverse group of Antarctic fishes. Their taxonomy is not well studied and many of the species are very similar making identifications tricky from photographs alone. This species is a large benthic predator. Only one of these individuals was recovered in the trawl. Species tentatively identified by University of Hawaii graduate student Astrid Leitner. Date: April 12, 2016. Photo by Maria Stenzel.
Ophthalmolycus sp (eelpout) retrieved from a depth of 480 to 500 meters in the middle basin of Andvord Bay, western Antarctic Peninsula. This genera of eelpouts (family Zoarcidae) has a dark blue abdomen and very thin almost translucent skin. They reside on the seafloor and are often seen with their eel-like bodies curled up in sinuous ‘S’ shapes. They are often seen moving slowly across the seafloor almost walking along using their large pectoral fins. These animals were quite common in the trawl. Species tentatively identified by University of Hawaii graduate student Astrid Leitner. Date: April 12, 2016. Photo by Maria Stenzel.
Chaenocephalus aceratus (ice fish) retrieved from a depth of 480 to 500 meters in the middle basin of Andvord Bay, western Antarctic Peninsula. Icefish are unique among vertebrates because they have translucent blood. In fact their hearts are white! This occurs because these fish do not use hemoglobin to transport oxygen in their blood. How they manage to maintain high levels of activities, for example actively hunting fish and krill, is a topic of ongoing research. These fishes also have antifreeze proteins in their blood which prevents their blood from freezing at the normal freezing point of seawater. Species tentatively identified by University of Hawaii graduate student Astrid Leitner. Date: April 12, 2016. Photo by Maria Stenzel.