Pouched lamprey

The pouched lamprey (Geotria australis), also known as wide-mouthed lamprey, is the only species in genus Geotria, which is in turn the only genus in the family Geotriidae.[3] It is native to the southern hemisphere. It spends the early part of its life in fresh water, migrating to the sea as adult, and returning to fresh water to spawn and die.

Pouched lamprey
Drawing by W. Wing
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Cephalaspidomorphi
Order:
Petromyzontiformes
Family:
Geotriidae

Genus:
Geotria

Species:
G. australis
Binomial name
Geotria australis
Synonyms[1][2]

Description
Geotria australis, Northland, New Zealand

G. australis, like other lampreys, has a thin eel-like body, and grows up to 60 cm (24 in) long.[4] It has two low dorsal fins on the back half. Like other lampreys, it has no jaws, only a sucker. The skin is a striking silver in adult lampreys caught fresh from the sea but soon changes to brown after they have been in fresh water for some time, due to deposition of biliverdin.[5] Adult eyes are relatively small and located on the side of the head. When fully mature, males develop a baggy pouch under their eyes, the function of which is unknown. However, there have been suggestions that the pouch in northern hemisphere species has been used by males during breeding times for gathering stones to make a nest.[6]

Life cycle

The freshwater ammocoete or larval stage of the life cycle are a dull brown in colour for most of their lives. Ammocoetes remain in fresh water for about four years until undergoing a six-month metamorphosis,[7] changing to silver with blue-green stripes.[5] The central nervous system of the pouched lamprey develops notably during metamorphosis to the large-eyed macropthalmia stage, with particularly large increases in the volume of visual areas of the brain.[8] At this point they migrate downstream to the sea.

Adults spend some of their life in the open sea, living as a parasite on other fish. They attach themselves to the gills or side of the fish and rasp at the tissues below. Adults return to fresh water to breed, spending up to eighteen months sexually maturing before spawning. Adults have been recorded living up to 105 days after spawning and wrapping themselves around egg masses to provide parental care.[9]

Distribution and habitat

The pouched lamprey is widespread in the Southern Hemisphere, occurring in New Zealand, Chile, Argentina, the Falkland Islands, South Georgia and the southwest and southeast corners of Australia.[3]

Threats

Lampreys are preyed on by albatrosses, shags, large fish and marine mammals.[3] It has been hypothesised that the apparent decline in lamprey numbers could be caused by the degradation of water quality in lowland waterways.[3]

References
  1. Froese, R.; Pauly, D. (2017). "Geotriidae". FishBase version (02/2017). Retrieved 18 May 2017.
  2. "Geotriidae" (PDF). Deeplyfish. Retrieved 18 May 2017.
  3. Roberts, Clive; Stewart, A. L.; Struthers, Carl D.; Barker, Jeremy; Kortet, Salme; Freeborn, Michelle (2015). The fishes of New Zealand. 2. Wellington, New Zealand: Te Papa Press. p. 36. ISBN 9780994104168. OCLC 908128805.
  4. Dianne J. Bray & Martin F. Gomon. (2011), Pouched Lamprey Geotria australis, in Fishes of Australia, accessed 07 Oct 2014, http://www.fishesofaustralia.net.au/home/species/3415
  5. Todd, P. R.; Wilson, R. D. (1983). "Epidermal pigmentation and liver coloration in the southern hemisphere lamprey, Geotria austral is Gray". New Zealand Journal of Marine and Freshwater Research. 17: 21–26. doi:10.1080/00288330.1983.9515983.
  6. Monette, S. N.; Renaud, C. B. (2005). "The gular pouch in northern hemisphere parasitic lampreys (Petromyzontidae)". Canadian Journal of Zoology. 83 (4): 527–535. doi:10.1139/z05-037.
  7. "Geotria australis: Pouched lamprey". Fishbase. Retrieved 2013-12-15.
  8. Salas; et al. (2015). "Ontogenetic shifts in brain scaling reflect behavioral changes in the life cycle of the pouched lamprey Geotria australis". Frontiers in Neuroscience. 9: 251. doi:10.3389/fnins.2015.00251. PMC 4517384. PMID 26283894.
  9. Baker, Cindy; Jellyman, Don; Reeve, Kathryn; Crow, Shannan; Stewart, Michael; Buchinger, Tyler John; Li, Weiming (2017). "First observations of spawning nests in the pouched lamprey Geotria australis". Canadian Journal of Fisheries and Aquatic Sciences. 74 (10): 1603–1611. doi:10.1139/cjfas-2016-0292. hdl:1807/77815. ISSN 0706-652X.
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