The common galaxias (''Galaxias maculatus'') or inanga (from the

Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the Co ...

''īnanga'' or ''īnaka'') is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

from the family

Galaxiidae 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 th ...

that is widespread in the Southern Hemisphere. It is migratory, living in

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include ...

but

spawning Spawn is the Egg cell, eggs and Spermatozoa, sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of freely releasing eggs and sperm into a body of water (fresh or marine); the physical act is ...

river mouth A river mouth is where a river flows into a larger body of water, such as another river, a lake/reservoir, a bay/gulf, a sea, or an ocean. At the river mouth, sediments are often deposited due to the slowing of the current, reducing the carryin ...

s, spending the first six months of its life at sea, and returning ''en masse'' in spring. Its

vernacular name Vernacular is the ordinary, informal, spoken form of language, particularly when perceived as having lower social status or less prestige than standard language, which is more codified, institutionally promoted, literary, or formal. More n ...

s include cowfish, jollytail, common jollytail, eel gudgeon, inaka, native trout, pulangi, puye, slippery tarki, spotted minnow, Falklands minnow and whitebait.

Description

Common galaxias is a slim, narrow fish with a mottled, spotty pattern, iridescent silver eyes, undersides and gill covers, and some individuals have an iridescent green stripe along the top of their bodies which can be intermittently seen as they swim. Their

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

''maculatus'' ("spotted") comes from the pattern of dark-mottled, leopard-like spots on an olive-brown background along their upper bodies. This pattern ranges from very subtle to quite bold. Common galaxias have slightly forked tails, unlike other most other galaxiids, which have square tails. Fully grown adults typically range from in length, with an average of . The maximum reported length is .

Distribution and habitat

Common galaxias are one of the most widely distributed freshwater fish in the world. They inhabit

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

(35–55°S),

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

, the

Falkland Islands The Falkland Islands (; ), commonly referred to as The Falklands, is an archipelago in the South Atlantic Ocean on the Patagonian Shelf. The principal islands are about east of South America's southern Patagonian coast and from Cape Dub ...

, some

Pacific Islands The Pacific islands are a group of islands in the Pacific Ocean. They are further categorized into three major island groups: Melanesia, Micronesia, and Polynesia. Depending on the context, the term ''Pacific Islands'' may refer to one of several ...

such as

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

, coastal streams in south-eastern

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...

, and

southwest The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A '' compass rose'' is primarily composed of four cardinal directions—north, east, south, and west— ...

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

and numerous waterfilled cenotes and caves in south-eastern

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...

. They are commonly found in small schools or shoals in slow-moving water, but can be more solitary in swifter streams. Adults are mainly found in still or slow-moving water in the lower parts of coastal streams and rivers, or around the edges of

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...

s; they can tolerate a wide range of natural conditions. If oxygen levels are low as a result of

eutrophication Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...

, they can jump out of the water (emerse) and take up oxygen through their skin as a last resort.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. They need access to

riparian A riparian zone or riparian area is the interface between land and a river or stream. In some regions, the terms riparian woodland, riparian forest, riparian buffer zone, riparian corridor, and riparian strip are used to characterize a ripar ...

vegetation for spawning, and usually live in river systems with access to the sea, as their

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

l stage is marine. They tend to be found in lower-elevation streams as, unlike other species of ''Galaxias'', they cannot climb past waterfalls. Common galaxias can become land-locked (such as in five lakes in Northland, New Zealand), feeding and breeding in large beds of reeds.

Life history

This species is usually considered

amphidromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousa ...

, a particular type of diadromy meaning that reproduction occurs in fresh water and larval growth occurs in the sea.

Reproduction

Adult fish typically reach sexual maturity at one year and spawning is triggered by changes in day length and temperature. Unless landlocked within a lake, the common galaxias spawns mainly in autumn during

spring tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

s in the tidally influenced reaches of rivers and streams but spawning in winter and spring has occurred. The eggs are laid ''en masse'' amongst flooded

vegetation by females. Male fish then release

sperm Sperm (: sperm or sperms) is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm ...

into the water and the eggs are fertilised externally. This type of spawning is called

polygynandry Polygynandry is a mating system in which both males and females have multiple mating partners during a breeding season. In sexually reproducing diploid animals, different mating strategies are employed by males and females, because the cost of gam ...

. Eggs remain attached to the vegetation as the tide recedes. Two types of reproductive strategy occur: the most common is a 'boom bust' strategy whereby spawning occurs in one event and is followed by death (

semelparity Semelparity and iteroparity are two contrasting reproductive strategies available to living organisms. A species is considered ''semelparous'' if it is characterized by a single reproduction, reproductive episode before death, and ''iteroparous ...

), or much more rarely spawning occurs in multiple years before death iteroparity.

Egg development

Eggs (about 1 mm diameter) develop at the base of vegetation for 2–4 weeks. Environmental conditions in the vegetation (particularly temperature and humidity) are critical for successful egg development. Egg mortality occurs from excess exposure to sunlight,

predation Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

from mice and spiders, grazing and trampling by livestock, mowing of bankside vegetation in urban areas, and flooding. The following spring tide floods the eggs stimulating them to hatch.

Marine life

After hatching, the 7-mm-long

e are swept out to sea and spend 3–6 months in the marine environment. This phase of their lifecycle is little understood, as the larvae are small, transparent, and difficult to locate. The speed and direction of ocean currents play an important role in their dispersal; temperature and food availability are also important in determining how long they spend at sea. This marine dispersal phase is a critical part of the common galaxias's lifecycle, because it gives larvae from different populations or rivers the opportunity to 'connect'. When the juveniles are sufficiently grown, about 30–55 mm in length, they migrate back into fresh water. The juveniles form large shoals as they move through estuaries. Some of their life is spent in the lower reaches of rivers, where they

metamorphose Metamorphosis is a biological process by which an animal physically developmental biology, develops including birth, birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through ...

, before spending their adult life in suitable freshwater habitat. Some individuals return to the river they were born in (

natal homing Natal homing, or natal philopatry, is the homing process by which some adult animals that have migrated away from their juvenile habitats return to their birthplace to reproduce. This process is primarily used by aquatic animals such as sea tur ...

), but most return to rivers other than their birth site.

Freshwater life

Following metamorphosis, adult spend around 6 months in fresh water, where they gain sufficient growth and energy to begin investing in reproduction. Males generally reach sexual maturity earlier and at a smaller size than females.

Parasites

In New Zealand, '' Deretrema philippae'' (=''Limnoderetrema minutum'') is known to

parasitise Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

the

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. T ...

(and possibly

gall bladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, althoug ...

) of the common galaxias. Similarly, the

intestinal parasite An intestinal parasite infection is a condition in which a parasite infects the gastro-intestinal tract of humans and other animals. Such parasites can live anywhere in the body, but most prefer the intestinal wall. Routes of exposure and inf ...

'' Steganoderma szidati'' has been reported from this species' Argentinian population. These are

digenea Digenea (Gr. ''Dis'' – double, ''Genos'' – race) is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms (known as ''flukes'') with a syncytial tegument and, usually, two suckers, one ventral and one or ...

flatworm Platyhelminthes (from the Greek language, Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") is a Phylum (biology), phylum of relatively simple bilaterian, Segmentation (biology), ...

Fishing

The juveniles are caught as

whitebait Whitebait is a collective term for the immature fry of fish, typically between long. Such young fish often travel together in schools along coasts, and move into estuaries and sometimes up rivers where they can be easily caught using fine-mes ...

while moving upstream and are much valued as a delicacy, leading to their protection with controlled fishing seasons 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 to preserve the adult population, but others ban it altogether unless the fisher belongs to an indigenous people (e.g., New Zealand

). For instance, in Tasmania, the adult common galaxias may only be caught using a pole of a specified maximum size (1 m).

Conservation

Galaxiid species are, in general, threatened by human activities such as intensive agriculture and land change use. These activities have removed vegetation from stream banks that are needed for spawning to protect eggs from the sun. The increased nutrient input into streams from farming can lead to eutrophication. In New Zealand, their conservation status is declining, mostly because of habitat loss and degradation. As adults, common galaxias eat

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s, and

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s. This is the same diet as introduced

trout Trout (: trout) is a generic common name for numerous species of carnivorous freshwater ray-finned fishes belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of which are members of the subfamily Salmoninae in the ...

, which not only compete for food, but also readily eat them. In areas where trout have become naturalised, common galaxias are scarce. Common galaxias, therefore, are mostly found in stretches of streams and rivers that are less suitable for introduced trout.

Restoration

In parts of New Zealand, this species' spawning habitat has become degraded due to activities related to agriculture, urbanisation, and land-use change. This creates sink populations in rivers as adult fish have nowhere suitable to lay their eggs and the majority of eggs die. Because these sink rivers produce no eggs or larvae, a gap is created during marine dispersal. No opportunities exist for the exchange of larvae from these sink populations with other populations. However, these sink populations can receive larvae that were born in different rivers. They will not be able to successfully reproduce and the sink cycle continues. Innovative methods to restore the riparian spawning habitat include using straw bales as a temporary replacement for vegetation. Straw bales provide the same conditions and physical structure as natural vegetation, enabling the eggs to develop successfully. This method ensures that eggs and larvae are produced, and that each river is a source of larvae. Exclusion of livestock and fencing of the bank-side vegetation is also an effective method to encourage regrowth of suitable vegetation. Restoration of the spawning habitat helps to maintain connectivity between larvae from different rivers during marine dispersal.

References

* * 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. (HTML abstract)

External links

* * *
Native Fish Australia
* https://web.archive.org/web/20081015114538/http://www.niwascience.co.nz/rc/freshwater/fishatlas/species/inanga NIWA June 2006

TerraNature, Auckland 2010 * Inanga on RadioNZ ''Critter of the Week''
13 May 2016
{{Taxonbar, from=Q44229 Galaxias Freshwater fish of Australia Freshwater fish of New Zealand Freshwater fish of Chile Freshwater fish of Argentina