The common river galaxias or Canterbury galaxias (''Galaxias vulgaris'') is a

galaxiid The Galaxiidae are a family of mostly small freshwater fish in the Southern Hemisphere. The majority live in Southern Australia or New Zealand, but some are found in South Africa, southern South America, Lord Howe Island, New Caledonia, and the ...

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

of the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Galaxias ''Galaxias'' is a genus of small freshwater fish in the family (biology), family Galaxiidae, and are frequently referred to as the galaxiids. These highly adaptable fish are typically found at temperate latitudes across the Southern Hemisphere. ...

'', found only in

Canterbury Canterbury (, ) is a City status in the United Kingdom, cathedral city and UNESCO World Heritage Site, situated in the heart of the City of Canterbury local government district of Kent, England. It lies on the River Stour, Kent, River Stour. ...

, New Zealand.

Description

''Galaxias vulgaris'' are a small freshwater fish which usually grow to 100–115 mm in length. They have a large mouth with a somewhat undercut lower jaw, pinched nostrils and a rounded snout.McQueen, S. (2013). ''A Photographic Guide to Freshwater Fishes of New Zealand''. pp. 48–49. Auckland, New Zealand, New Holland. The fins are thick and fleshy. The pectoral fins are low and downturned. The caudal peduncle long and slender, the length of which is about 1.5 times the depth. They are a speckled brown/grey/olive to match the gravel substrate in which they live and have highly variable black banding or blotching along their back.McDowall, R. M. (1990). ''New Zealand Freshwater Fishes: A natural history and guide''. pp. 133–117. Wellington, New Zealand, Heinemann Reed. This

pigmentation A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...

is so effective as a

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the ...

, that it allows them to move out from the sanctuary under the rocks and spend time in the more open river in relative safety. They are easily confused with koaro which are slightly angled towards each other, but the eyes of ''G. vulgaris'' are larger and angled towards each other so the eyes are more visible when viewed from above. ''Galaxias vulgaris'' can be further distinguished from other ''Galaxid'' species by its less dense mottled pigmentations, a slightly larger and wider body than other species.

Distribution

''Galaxias vulgaris'' are found in rivers and streams throughout the

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...

(with the exception of

Banks Peninsula Banks Peninsula is a peninsula of volcanic origin on the east coast of the South Island of New Zealand. It has an area of approximately and encompasses two large harbours and many smaller bays and coves. The South Island's largest cit ...

and in eastern Otago. The distribution ranges from low to high elevations in the shallow waters of rivers and streams. It is no longer found in many of the main river systems due to predation from introduced trout species ''Oncorhynchus mykiss'' (

rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...

), and ''Salmo trutta'' (

brown trout The brown trout (''Salmo trutta'') is a European species of salmonid fish that has been widely introduced into suitable environments globally. It includes purely freshwater populations, referred to as the riverine ecotype, ''Salmo trutta'' morph ...

Habitat preferences

Preferred habitat of ''Galaxias vulgaris'' is fast flowing sections of stream which are well aerated and with open tussock grassland. Here, they inhabit the areas between and under rocks during the day and venture out into the more open areas of water to feed in the evening and night as ''Galaxias vulgaris'' generalized is solitary, nocturnal and largely cryptic invertebrate predator. Due to introduced trout, they are often excluded from the main base of rivers, or smaller over crowded rivers, but they can be found in side braids and tributaries. As ''Galaxais vulgaris'' is a non-migratory fish, populations are confined to the river systems in which they are born. As they do not enter marine environments they become isolated from populations in other water systems. Often, the only interaction between populations in different rivers is during heavy flooding events.The ecology of ''Galaxias vulgaris'' in the river Glentui, Canterbury, New Zealand
Doctoral thesis, University of Canterbury.

Life cycle/phenology

Unlike many other species in the genus, ''Galaxis vulgaris'' is a non-migratory species and complete their entire life cycle in freshwater.

Spawning Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquati ...

occurs from August to September. This involves the females laying hundreds to thousands of eggs beneath boulders in the stream, (the number of eggs laid is dependent of favourable or unfavourable environmental conditionsJones, P. E. (2014)
Life history variation in the ''Galaxias vulgaris'' complex: implications for interactions with invasive salmonids
Doctoral thesis, University of Otago, 2014.) and the male

fertilizing Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

and temporarily guarding the eggs. The ‘nest’ is excavated by the male fish, and will generally be laid in by multiple females. Jones states that ''Galaxis vulgaris'' lay comparatively small eggs and have a higher fecundity (reproductive rate), than other non-migratory freshwater fish species. This allows relatively rapid colonization and re-colonization of habitat. The presence of predatory species, combine with late maturation and high juvenile mortality currently mitigates their ability increase their populations. Cadwallader found a very high mortality among adults, particularly males, post reproduction. The larvae (7–8 mm) hatch from the eggs after 3–4 weeks and form shoals in the slow flowing stream margins. They remain in these shoals until they become approximately 35 mm in length. At this size they have developed camouflage needed to blend into the gravel substrate, and separate from the shoal. Cadwallader found that the juveniles became mature and able to reproduce during early autumn. He also found that the trigger for sexual maturation was primarily controlled by fish size rather than time of year. This mean value for this threshold for sexual maturation was found to be approximately 59 mm in length.

Diet and foraging

''Galaxis vulgaris'' primarily feed on the nymphs and larvae of

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s. It is a predominately bottom dwelling fish, which feeds in both drift and benthos methods. It has been “observed that ''Galaxias vulgaris'' is nocturnally active. During the day the fish remained hidden in the substrate of the stream simulator. Immediately following emergence after sunset they took up drift-feeding stations in the water column, and later in the night switched to feeding on benthos”. This is done in the evening and night as they spend the daytime hidden under rocks and in the gravel substrate. They feed into the current and pick up their food as it gets washed towards them. Their food consists of small stream invertebrates such as stoneflies and mayflies and while feeding during drift, preferring larger prey. Cadwallader found that individuals in slow moving areas of water would feed at mid-water in a similar fashion to introduced

trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salmoni ...

species. His study of the stomach composition of ''Galaxias vulgaris'' showed high abundances of Trichoptera (

caddisfly The caddisflies, or order Trichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the b ...

) larvae, Corydalinae (

dobsonfly Dobsonflies are a subfamily of insects, Corydalinae, part of the Megalopteran family (biology), family Corydalidae. The larvae (commonly called hellgrammites) are aquatic insect, aquatic, living in streams, and the adults are often found along s ...

) larvae, ''Deleatidium'' sp. (

mayfly Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the ord ...

) larvae, aquatic Diptera, Elimidae (

midges A midge is any small fly, including species in several families of non-mosquito Nematoceran Diptera. Midges are found (seasonally or otherwise) on practically every land area outside permanently arid deserts and the frigid zones. Some midg ...

) adults and larvae, and terrestrial insects.

Predators, parasites, and diseases

The key predator of ''Galaxias vulgaris'' are the

salmonids Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whitefi ...

''Oncorhynchus mykiss'' (rainbow trout) and ''Salmo trutta'' (brown trout). Woodford and McIntosh found that populations of ''Galaxis vulgaris'' were heavily impacted by trout populations. Conversely, populations which were free from trout predation (usually due to

geographic isolation Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

) were at a higher altitude and were more stable than those in the presence of trout. Predation from trout occurs on ''Galaxias vulgaris'' at all stages of their lifecycles so there is no predation safe size threshold, however juveniles are particularly susceptible to predation from trout of all sizes.

Cultural uses

There is no cultural use of ''Galaxias vulgaris''.

Protection and conservation

In 2014 the New Zealand

Department of Conservation An environmental ministry is a national or subnational government agency politically responsible for the environment and/or natural resources. Various other names are commonly used to identify such agencies, such as Ministry of the Environment ...

classified G. vulgaris as "At Risk: Declining" with the qualifier "A(2/1) - Total area of occupancy ≤ 1000 ha (10 km2), predicted decline 10–30%". Also in 2014 the

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

rated the SPECIES as "Least Concern", noting that rates of decline are slow. The ranges where the Galaxias vulgaris inhabit are with in New Zealand's

managed areas which means that these areas are protected, though there is still a large threat from the invasive salmonids. Habitat loss due to increasing irrigation from agricultural land use change is a threat to ''Galaxias vulgaris''. The International Union for Conservation of Nature notes that there is an increased risk of habitat loss post

tenure review Tenure review is a process of reviewing the leasehold tenure of some high country land in the South Island of New Zealand. It currently involves 20% of the South Island or 10% of the total land area of New Zealand. Tenure review began with the pa ...

in the high country. Much of the land which became freehold incorporates the habitat of ''Galaxias vulgaris'' and now has the potential to be altered for farming purposes, endangering the habitat of ''Galaxias vulgaris''. ''Galaxias vulgaris'' is however classified as Not Threatened.