Emerald notothen or emerald rockcod Trematomus bernacchii

Trematomus bernacchii is found throughout Antarctica and the Antarctic Peninsula, South Shetland Islands, South Orkney Islands and Peter I Island from the shore to 695 meters depth [8,13]. T. bernacchii is commonly found within the first 200 meters of depth but it can be found down to 700 meters [1]. T. bernacchii has been observed taking refuge within volcano sponges with their heads sticking out [2].

Trematomus bernacchii has two morphs, with or without a white blotch spreading out on the nape, behind the eyes, and before the pectoral fins [11,12]. T. bernacchii has black or dark brown blotches over a pale brown or pink-brown body that is darker dorsally; its dorsal and anal fins are uniformly light-brown [8]. The pectoral fins of T. bernacchii are dark with numerous light spots and it has three green spots on the upper part of the pectoral fin base [8].

In deeper water, Trematomus bernacchii can be less pigmented and more pinkish-brown in coloration as shown here [9].

T. bernacchii females can be up to 35 centimeters long, and males up to 28 centimeters long; females live up to 21 years, and males up to 16 years [1,19].

Trematomus bernacchii lives on the seafloor (benthic) and is primarily a benthic feeder, eating sedentary and moving prey, by ambush or hunt- and-peck feeding [1,2,3,4,7,8,10,14].

Trematomus bernacchii has a varied diet: algae; testate amoeba Gromia; crustaceans (including euphausiid krill, mysids, copepods, pycnogonids, tanaids, cumaceans, ostracods, isopods, amphipods, shrimp); nemerteans; sipunculids; priapulids; nematodes; oligochaetes; pterobranchs; polychaetes; hydroids; soft coral (including Clavularia); medusae; anemone Edwardsia meridionalis; echinoderms (holothurians, brittle stars, sea urchin Sterechinus neumayeri); bivalves; gastropods; tunicates; thaliaceans; fish; and fish eggs [1,2,3,4,7,8,10,14,16,17,18,19,23].

Spawning takes place in December-January in McMurdo Sound and in October-November in other reported areas [1]. Trematomus bernacchii deposits its eggs on the seafloor (demersal) or within volcano sponges like Rosella nuda; parental guarding of the egg mass within volcano sponges has been observed [2]. Hatching may occur towards the end of summer or early autumn [1].

Antarctic fish like Trematomus bernacchii are well-adapted to the extremely low and stable temperatures of McMurdo Sound where seawater has a nearly constant mean annual temperature of -1.86 degrees Celsius (28.65 degrees Fahrenheit) and temperature doesn't vary much with depth or season -- 0.2 degrees Celsius (0.36 degrees Fahrenheit) [5].

The flip side is that Trematomus bernacchii and some other cold-adapted Antarctic fish die of heat at approximately 6 degrees Celsius (42.8 degrees Fahrenheit) which is the lowest known heat death temperature of any animal [6]. This freezing resistance is accomplished with special antifreeze glycopeptides in its body fluids, that bind to emerging ice crystals and prevent their growth; these antifreeze compounds are being commercially marketed for product development [15,20].



The species name bernacchii honors L.O. Bernacchi, an Australian physicist-meteorologist who collected on the Southern Cross Expedition and who also served on Scott's 1901 expedition.

Taxonomic Note: Some use the genus Pseudotrematomus [1,21,22]

1: Fishes of the Southern Ocean. O Gon and PC Heemstra, eds. Grahamstown, South Africa : JLB Smith Institute of Ichthyology, 1990. pp. 317-318; 2: Copeia 1980(1):171-173; 3: Polar Biology 4:155-160, 1985; 4: Polar Biology 13(6):429-431, 1993; 5: Antarctic Research Series 5, Biology of the Antarctic Seas II. GA Llano, ed. Washington DC : American Geophysical Union, pp1-37; 6: Science 156:257-258, 1967; 7: Antarctic Science 6(1):61-65, 1994; 8: FAO Species Identification Sheets for Fishery Purposes : Southern Ocean (Fishing Areas 48, 58 and 88) (CCAMLR Convention Area) / W Fischer & JC Hureau, eds. Rome : Food and Agriculture Organization of the United Nations, 1985; 9: Art De Vries, personal communication, 1998; 10: Bulletin de l'Institut Oceanographique 66(1368), 1966; 11: Biochemical Systematics and Ecology 20(3):233-241, 1992; 12: Antarctic Science 9(4):381-385, 1997; 13: Tethys 6(3):631-653, 1974; 14: Antarctic Science 12(1):64-68, 2000;15: www.afprotein.com; 16: Ophelia 24(3):155- 175, 1985; 17: Polar Biology 13:291-296, 1993; 18: Ross Sea Ecology : Italiantartide Expeditions (1987-1995). FM Faranda, L Guglielmo, A Ianora, eds. Berlin : Springer, 2000. pp. 551-561; 19: Ross Sea Ecology : Italiantartide Expeditions (1987-1995). FM Faranda, L Guglielmo, A Ianora, eds. Berlin : Springer, 2000. pp. 457-468; 20: Water and Life : Comparative Analysis of Water Relationships at the Organismic, Cellular, and Molecular Levels. GN Somero, CB Osmond, CL Bolis, eds. New York : Springer-Verlag, 1992. pp. 301-315; 21: History and Atlas of the Fishes of the Antarctic Ocean. RG Miller. Carson City, Nev. : Foresta Institute for Ocean and Mountain Studies, 1993; 22: Biologiia Shel’fovykh zon Mirovogo Okeana : tezisy dokladov Vtoroi vsesoiuznoi konferentsii po morskoi biologii, Vladivostok, sentiabr’ 1982 g. AI Kafanov & TS Veniaminson, eds. Vladivostok : DVNTS AN SSSR, 1982. Volume 2, pp. 9-10; 23: Polar Biology 27(11):721-728, 2004

Text ©Peter Brueggeman. Photographs ©M Dale Stokes & Norbert Wu. Photographs may not be used in any form without the express written permission of M Dale Stokes & Norbert Wu. Norbert Wu no longer grants permission for uncompensated use of his photos under any circumstances whatsoever; want more info?