Humped rockcod, humphead notothen
The species name gibberifrons is a combination of the words gibber, meaning 'humpback', and frons, meaning 'forehead', indicating a convex forehead. These fish are characterised by a steep snout profile, a narrow interorbital region (or interorbital space) and a humped forehead (the head is depressed behind the eyes). There are 1-2 rows of small conical teeth on each jaw and the gill crests are short. The entire body is yellowish with irregular dark patches and blotches on the upper part of the head and trunk. Juveniles have irregular transverse stripes on the body (divided into three or four rows of alternating spots), which are rarely present in adults. The fins are greenish (the only exception being the anal fin, which is pale with 2-3 horizontal stripes). The dorsal, caudal and pectoral fins have a number of brown spots forming horizontal stripes.
Widespread in the islands of the Scottish Arc (South Shetland Islands, South Orkney Islands, South Sandwich Islands and South Georgia), the northern Antarctic Peninsula and Heard Island in the Southern Ocean.
This species inhabits depths of 6-429 m (20-1,407 ft), but is most common at depths of 100-400 m (328-1,312 ft), such as around Elephant Island.
The maximum recorded length of this species is 55 cm, but 40 cm is more common. The age limit is 18 years. Maximum mass of 2 kg.
Life history and Behavior
Gobionotothen gibberifrons is a sedentary fish that only migrates within the shelves of the islands where it lives. The feeding aggregations off the South Orkney and South Shetland Islands form from December to May at depths of 150-500 metres. The densest aggregations are observed off Elephant Island in January-February.
Food and feeding habits
This species is a benthopelagic predator that feeds on polychaetes, echiurans, sipunculids, priapulids, bivalves and crustaceans. When krill are abundant, this species will actively feed on them. They will also select fish eggs when available. Predators include Notothenia rossii, Pseudochaenichthys georgianus, Chaenocephalus aceratus, Phalacrocorax atriceps and Arctocephalus gazella.
This species reaches sexual maturity at a height of 36 cm (14.2 in). Males first spawn at 36 centimeters (36 cm) and females first spawn at 38.6 centimeters (15.2 in). Mature females may spawn for the first time at 6-8 years of age, and up to 143,620 eggs up to 2.5 mm in diameter may be laid. Spawning occurs from late winter to early spring (exact months vary from place to place: e.g., August-September around Elephant Island and July-August on South Georgia). Hatching occurs in spring and early summer, and the length at hatching is about 7 mm long. Larvae emerge in the water column in September around South Georgia and November around Elephant Island. The larvae do not complete their pelagic phase until late summer and from this time onwards they switch to a benthopelagic lifestyle.
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