Icelandic threespine stickleback

The Icelandic threespine stickleback (Gasterosteus islandicus) is a freshwater fish, and one of the few vertebrate species endemic to Iceland. In some literature it is considered as a subspecies of G. aculeatus,^[2] though several authorities offer it full species status.^[3][4] It was first described by French biologist Henri Émile Sauvage in 1874.

Icelandic threespine stickleback
Specimen drawing of a sister species, Gasterosteus aculeatus
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Family:	Gasterosteidae
Genus:	Gasterosteus
Species:	G. islandicus
Binomial name
Gasterosteus islandicus Sauvage, 1874

Distribution

The Icelandic threespine stickleback is known from at least four different lakes in Iceland, including Þingvallavatn, Hreðavatn, Frostastaðavatn, and Mývatn. ^[5]

Description

The species is differentiated from other sticklebacks by having a deep notch on the anterior margin of the pelvic girdle. As opposed to other members of the genus, the Icelandic threespine stickleback has a trunk with 2-15 scutes, sometimes including scutes forming a lateral keel on the caudal peduncle or with the keel being absent. In the various lakes it occurs in, there are morphological differences reported between individuals depending on the local substrates (mud, gravel, lava, etc.), especially in Þingvallavatn.^[6]