1. Figure 4: Vental surface of adult koaro
(McDowall, 2003)
Figure 3: Image of koaro jaw and ventrally flared
pectoral fin (DOC, 2005)
References
Bell, C. (2001). The ecology of koaro (Galaxias brevipinnis) in Manson Creek, North Canterbury. University of Canterbury, Christchurchs
Goodman, J., Dunn, N., Ravenscroft, P. Allibone, R., Boubee, J., David, B., Griffiths, M., Ling, N., Hitchmough, R. & Rolfe, J. (2013). Conservation status of New Zealand freshwater fish, 2013.
Department of Conservation: Wellington, New Zealand
Gross, M., Coleman, R. & McDowall, R. (1988). Aquatic productivity and the evolution of diadromous fish migration. Science 239: 1291-1293
Department of Conservation. (2016). Freshwater fish:whitebait-migratory galaxiids. Retrieved 23rd March, 2016 from http://www.doc.govt.nz/nature/native-animals/freshwater-fish/whitebait-migratory-
galaxiids/
Department of Conservation. (2005). New Zealand large galaxiid recovery plan, 2003-2013: Short jaw kokopu, giant kokopu, banded kokopu and koaro. Wellington.
McDowall, R. (2010). New Zealand freshwater fishes: an historical and ecological biogeography. Springer Dordrecht Heidlberg; London
McDowall, R. (2003). Native freshwater fish: The key to climbing in the koaro. NIWA: Christchurch
McDowall, R. (2000). A Reed field guide to New Zealand freshwater fishes. Reed Publishing: Auckland
McDowal, R. (1991). Conservation and Management of the Whitebait Fishery. Science and Research series No.38, Department of Conservation: Wellington.
Niwa. (2016). Koaro distribution map. Retrieved March 22, 2016 from https://www.niwa.co.nz/freshwater-and-estuaries/nzffd/NIWA-fish-atlas/fish-species/koaro
Rowe, D., Smith, J. & Grayling, S. (2008) Status of koaro (Galaxias brevipinnis) populations in the Te Arawa lakes and options for their restoration. National Institute of Water and Atmosphere
Research Ltd; Hamilton, New Zealand
Whitebait Connection. (2016). Gallery. Retrieved on 22 March, 2016 from http://www.whitebaitconnection.co.nz/gallery_page.php?gallery_id=49d97c37c03e2
Sexual maturity is reached after 2 years.
Spawning occurs in
the headwaters of
rivers and streams,
along stream banks,
during autumn and
early winter.
Larvae hatch and are swept downstream and enter
marine environment, growing quickly due to the
abundance of food.
During spring, when they are 50mm in length and 6
months old, they migrate from the sea back into river
systems as juveniles.
Illustrations by: Emily Lloyd
Emily Lloyd
Koaro generally prefer rocky, fast flowing, tumbling streams, with boulder, cobble or pebbly beds of small
tomoderatesize.Streamsareeitherinnativeforest,ortussockstreamsthatdrainintohighelevationlakes.
The presence of spawning habitat, forest cover, presence of refuge, access to suitable food resources and
vulnerabilitytocompetitionorpredationbytroutarefactorsthataffectlocalassemblagesofkoaro(Bell,2001).
The diet of a koaro varies depending on the stage in their life cycle. Juvenile koaro feed mainly on Daphina
andplankton,feedingaspelagiclarvae,whilemorematurefisharebenthicfeeders,feedingpredominately
on benthic invertebrates. Koaro are non-selective feeders (Bell, 2001), feeding on a wide variety of
invertebratetaxadependantontheirlocalenvironment,includingTrichoptera,Ephemeropteraandaquatic
Dipteralarvae.Adultkoarohavebeenfoundtosometimesfeedonjuvenilekoaro,rainbowtroutandkoaro
ova, crustaceans, and have been known to take terrestrial prey when drift feeding in riffles (Bell, 2001).
Diet and habitat
Morphology, physiology and behavioural adaptations
Koaro (Galaxias brevipinnis)
Figure 1: Distribution map of koaro
(NIWA, 2016)
Figure 2: Image of koaro (Whitebait
Connection, 2016)
Introduction
Koaro (Galaxias brevipinnis) is part of the family Galaxiidae, found only in the southern hemisphere. They
areindingenoustoNewZealand,andarefoundthroughoutthecountryincludingStewartIsland(McDowall,
1991)(figure 1), and on more remote islands including Chatham, Auckland and Campbell Island’s, as well
as Tasmania, in southeastern Australia. They are present from sea level to long distances inland, up to
990m in elevation and 400km inland, and are the second most common, and the most widespread of the
five diadromous galaxiid species. Koaro have developed morphological, physiological and behavioural
adaptations that have enabled them to become a successful species of freshwater fish in New Zealand.
Koaro is not a protected freshwater fish, and its juvenile stage is part of the whitebait catch for
recreational and commercial fishers. Their conservation status, under the Department of Conservations
threat classification, is low compared to other galaxiid species, however they are still classed as ‘at risk’.
Biology and Ecology
Koaroarecrypticfish,havinganocturnalandsolitarylifestyle,theycanexistundetectedinplaces.Koaroarea
relativelylargegalaxiidfish,typicallygrowingupto160-180mminlengthatmatureadultsize,andhavebeen
foundtobe280mm(McDowall,2000).Theyarealonglivedfish,livingforupto15yearsormore(DOC,2016).
They are negatively buoyant, slender with an elongated tubular body form (figure 2). They have a short
flattenedhead,allowingthemtoaccessinsectsamongrocksandbounders,andalargemouththatreaches
back below the eyes, containing a lower jaw that distinctly shorter than the upper jaw (figure 3), and
strong lateral canine teeth. The skin is tough and leathery, containing no scales, instead it has a protective
mucus layer that protects the fish against fungal growth. The pattern on the skin reflects an irregular
array of blotches and stripes, with pigmentation ranging from dull green to olive brown, often containing
gold flecks on their head and dorsal surface, and with lighter colouration on ventral surface (figure 2).
Koaro’s widespread distribution can be accredited to their diadromous behaviour, where they
migrate between salt and freshwater during different phases of their life history. Koaro are
amphidromous, as spawning occurs in freshwater before larvae migrate to the sea immediately after
hatching, returning to freshwater as juveniles to grow and breed. This migratory behaviour gives
the koaro access to the sea and aids in its widespread distribution throughout New Zealand, off
shore islands and Tasmania. It also allows for resource partitioning within the species, where larvae
utilize resources in the sea, and juvenile and adult forms utilize resources in freshwater systems.
Koaro have accomplished climbing adaptations, giving them the ability to penetrate upstream, past
swift rapids, torrents and waterfalls up to 20-30m high, and enabling them to reach long distances
inland and to high altitudes. Their pectoral and pelvis fins are specially formed to face downwards,
be large and broad in shape, and ventrally flared to increase the surface area of the fish. These
adaptations aid in climbing, along with backwards facing ridges on the front part of the fin (figure 4),
giving them a grippy texture, as well as aid in position maintenance in the swift water habitats they are
often found. Climbing depends significantly on the use of water tension to adhere to damp surfaces
of wetted rock, and it is likely that only smaller juvenile koaro are able to climb substantially further
than larger adults (McDowall, 2010). Having the ability to infiltrate further up stream than most other
freshwater fish species, gives the koaro access to various well-suited habitats, without competition
for space and food resources from other species, contributing to their successful distribution.
Not all koaro populations are diadromous, inhabiting land-locked lakes, in both
the North and South Island, including Lake Tarawera, Taupo, Manapouri, and
Wanaka. Spawning occurs as normal, with the lakes acting as an ‘inland sea’,
which the larvae develop in. Juvenile koaro migrate back into the streams earlier
than marine diadromous fish would enter freshwater, however, adult koaro from
both populations grow just as large and as fast as each other (Gross et al, 1988).
Status of species and management
The conversation status of koaro is rated ‘at risk’, ‘declining’. The population is
in ‘partial decline’, with a large population (>100,000 individuals) and low to
high ongoing or predicted decline (10-70%) (Goodman et al, 2013). The koaro’s
widespreaddistributionandlargepopulationnumbersistheprobablecausetowhat
iskeepingthespeciesatthislowerthreatrate,comparedtotheothergalaxiidspecies.
Koaro have been drastically reduced in inland lakes in Te Arawa, central North
Island and South Island alpine lakes, confined to only a few tributary streams, or
completelylocallyextinct(Roweetal,2008).Thisispredominatelyduetointroduced
trout predating on, and outcompeting the koaro for food resources. Koaro are
also affected by land use changes, primarily the deforestation around stream
edges, and are now largely absent from streams beyond the forest margin. New
Zealand has a vast history of native forest clearance to create land for productive
landuses,significantlydestroyingandmodifyingriparianandcatchmenthabitats.
Koaro, in their juvenile stage, are one of the five galaxiid
species harvested and eaten as the delicacy whitebait. They
are the second most abundant species in New Zealand’s
whitebait catch, resulting in a large number of juvenile
koaro captured by commercial and recreational fishers. The
whitebait season is regulated from mid-August to the end
of November throughout New Zealand, except Westland,
and is prohibited for the rest of the year. There is no catch
limit, only restrictions on the size of the fishing gear.