Mesites maculatus Jenyns, 1842
The common galaxias or inanga (Galaxias maculatus), is a species of fish from the galaxiid family that is very widespread in the Southern Hemisphere. It is a slim narrow fish with a forked tail and as an adult it lives in freshwater rivers and lakes. The common galaxias grows to a length of 40 to 120 mm, but can grow up to 180 mm. The English vernacular names used for the species also include cowfish, jollytail, common jollytail, eel gudgeon, inaka, native trout, pulangi, slippery tarki, spotted minnow and whitebait.
Distribution and habitat
Common galaxias are one of the most widely distributed freshwater fish in the world and can be found around throughout New Zealand; in coastal streams in south eastern Australia, Tasmania and some parts of southwest Western Australia; in Chile (from 35–55°S); Patagonia, Argentina; in the Falkland Islands; and in some Pacific Islands such as New Caledonia.
Adults are mainly found in still or slow-moving water in the lower parts of coastal streams and rivers, or around the edges of lakes and lagoons. They are often found in small schools, and can tolerate a wide range of natural conditions.
Galaxiid species are, in general, threatened by human activities such as intensive agriculture, dairy, and land change use. These activities have worsened environmental conditions of the river banks (removal of vegetation and nutrient input), leading to eutrophication and subsequent hypoxia. Recent studies have shown that hypoxia imposes a significant challenge for the common galaxias, forcing them to jump out of the water (emerse) and take up oxygen through their skin as a last resort. This response, however, potentially increases the risks of desiccation and predation.
Unless within a landlocked lake, the common galaxias spawns downstream in rivers and streams amongst vegetation on the banks of the estuary regions during a spring tide mainly in autumn. The eggs remain on the bank (out of the water) until the next spring tide when they hatch into larvae which are swept out to the ocean. For the next 5–6 months the larvae live in the sea and develop into juvenile fish, often referred to as whitebait. When they are about 30 mm in length and 3–4 mm in width they swim up a river on the incoming tide until they reach a suitable habitat where they develop into the adult form. As adults they eat insects, crustaceans, and molluscs. This is the same diet as introduced trout, which not only compete for food but also readily eat them. In areas where trout have become naturalised, galaxias are scarce. Common galaxias, therefore, are mostly found in stretches of streams and rivers that are not suitable for introduced trout.
This species lives for about twelve months and usually dies after spawning.
In New Zealand, Deretrema philippae (=Limnoderetrema minutum) is known to parasitize the intestine (and possibly gall bladder) of the common galaxias. Similarly, the intestinal parasite Steganoderma szidati has been reported from this species' Argentinian population. These are digenean flatworms (Etchegoin et al. 2002).
The juveniles are caught as whitebait while moving upstream and are much valued as a delicacy leading to their protection with licensing and controlled fishing seasons in order to preserve adult populations. They are fished commercially in New Zealand, Chile and Argentina, but the last Australian commercial fishery closed in Tasmania in the 1970s.
Some jurisdictions permit fishing of the adults but again under regulation or licence in order to preserve the adult population, but others ban it altogether unless the fisher belongs to an indigenous people (e.g., New Zealand Māori). For instance, in Tasmania, the adult common galaxias may only be caught using a pole of a specified maximum size (one metre).
- Urbina M.A, Glover C.N., Foster M.E. 2012. A novel oxyconforming response in the freshwater fish Galaxias maculatus. Comparative Biochemistry and Physiology A 161, 301- 06.
- Urbina M.A and Glover C.N. 2012. Should I stay or should I go?: Physiological, metabolic and biochemical consequences of voluntary emersion upon aquatic hypoxia in the scaleless fish Galaxias maculatus. Journal of Comparative Physiology B. 182:1057–1067. doi: 10.1007/s00360-012-0678-3
- Urbina M.A, Foster M.E, Glover C.N. 2011. Leap of faith: Voluntary emersion behaviour and physiological adaptations to aerial exposure in a non-aestivating freshwater fish in response to aquatic hypoxia. Physiology and Behavior 103, 240-247.
- Urbina M.A., Meredith, A.S., Forster, M.E. & Glover, C. N. 2014. The importance of cutaneous gas exchange in aquatic and aerial mediums in galaxiid fishes. Journal of Fish Biology, specials issue on Airbreathing fish. 84(3), 759-773.
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- Froese, Rainer and Pauly, Daniel, eds. (2010). "Galaxias maculatus" in FishBase. July 2010 version.
- "Galaxias maculatus". Integrated Taxonomic Information System. Retrieved 18 April 2006.
- Etchegoin, Jorge A.; Cremonte, Florencia & Escalante, Alicia H. (2002): Steganoderma (Steganoderma) valchetensis n. sp. (Digenea: Zoogonidae) from the relict fish Gymnocharacinus bergi (Osteichthyes: Characidae) in Argentina. Systematic Parasitology 51(2): 149–153. doi: 10.1023/A:1014098732668 (HTML abstract)