Thebald notothen (Pagothenia borchgrevinki), also known as thebald rockcod, is a species of marineray-finned fish belonging to thefamilyNototheniidae, the notothens or cod icefishes. It is native to theSouthern Ocean.

Bald notothen
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Family:	Nototheniidae
Genus:	Pagothenia
Species:	P. borchgrevinki
Binomial name
Pagothenia borchgrevinki (Boulenger, 1902)
Synonyms
Trematomus borchgrevinkiBoulenger, 1902 Notothenia hodgsoniBoulenger, 1907

The bald notothen was first formallydescribed in 1907 asTrematomus borchgrevinki by the Belgian-born BritishichthyologistGeorge Albert Boulenger with thetype localities given as at the surface atDuke of York Island and atCape Adare.^[1] Thespecific name honoursCarsten Egeberg Borchgrevink who commanded theBritish Southern Cross Antarctic Expedition (1898–1900), during whichtypes were collected.^[2]

The bald notothen attains a maximumtotal length around 28 cm (11 in), it is yellow with dark spots and irregular crossbars. Itsdorsal andcaudal fins may occasionally also be spotted.^[3]

The bald notothen is found in the Southern Ocean where it has been recorded from theWeddell Sea, theRoss Sea, theDavis Sea, inVincennes Bay, and around theBudd Coast, theAntarctic Peninsula,South Orkneys, andSouth Shetland Islands. It can be found at depths from the surface to 550 m (1,800 ft), though it is much rarer below 30 m (98 ft). This species is cryopelagic and is often found along the under surfaces of ice foraging for prey such assympagiccopepods andkrill. In turn, it is known to be preyed upon by theploughfish (Gymnodraco acuticeps) and theAntarctic toothfish (Dissostichus mawsoni).Antifreeze proteins in its blood prevent it freezing in the subzero water temperatures ofAntarctica. The bald notothen is adapted to life in the water column as the shape and flatness of the trunk may streamline the fish and reduce drag. Thepelvic andanal fins do not have the adaptations for substrate contact borne by related benthic species. There are silvery reflective layers, calledstrata argentea below the skin which provide camouflage when the fish is seen against the background of platelet ice. Theretina had numerouscones suggesting that the eye is able to function during the day and at night.^[4] Sexually mature individuals of this species spawn once a year. The larvae have a longpelagic phase.^[3]

The bald notothen is of no interest tocommercial fisheries.^[3]