A newly described species. The majority of the following information is from Raadik (2014). Previously referred to as Galaxias sp. 1.
A moderate-sized galaxiid with truncate or slightly forked tail; the tail is usually longer than the caudal peduncle. The body is laterally compressed posterior to the pelvic fins, and strongly so for the caudal peduncle. Maximum recorded size is 133 mm (Length to Caudal Fork; LCF), and commonly 75–90 mm LCF.
The body is olive to grey-brown on the back and upper sides, becoming cream to white or silvery on lower sides, with a silvery belly.
The dorsal surface is overlain with dark brown to grey-brown spots that often combine to form irregular vertical dark bands or blotches, extending onto the upper sides. This pattern is not present on the head. The mid-dorsal surface between the neck and dorsal fin sometimes with a row of gold to coppery spots. The gill cover is translucent with a large turquoise, silvery or golden patch. The head is slightly to moderately wedge-shaped laterally, and the snout is rounded.
The mouth is moderate (reaching to below anterior of eye) and the upper jaw is slightly longer than lower jaw. The anal fin is longer than the dorsal, usually commencing under about 0.5 distance along the dorsal length.
Previously confused with Mountain galaxias (Galaxias olidus), the Obscure galaxias was only described as a separate species in 2014, and so many aspects of its ecology are unknown. However, some aspects are likely to be similar to other members of the Mountain galaxias complex.
Obscure galaxias occur in a range of stream sizes and types ranging from moderately fast-flowing small creeks to slow-flowing medium to large lowland rivers. It also occurs in billabongs, anabranches and some wetlands. Juveniles are found in shallow riffles on the edge of pools with adults more common in open water habitats in pools, and also glides. The species is usually found amongst dense aquatic vegetation and timber debris. In the Goulburn–Broken catchment in Vic it was found to occur mostly in comparatively larger streams at lower elevation, with higher and more variable flow.
The spawning period extends from late May to early July but has been known to extend into August. Fecundity is relatively high with >2000 small (mean diam. 1.1 mm), circular, orange unshed mature eggs in a 106 mm female in mid-May. Spawning site is unknown, but spawning is likely to occur on the underside of cobbles in riffles (as it does for Mountain galaxias, Stocky galaxias, Barred galaxias and Ornate galaxias). Spawning cues and time to hatching are unknown. Movement requirements are also unknown, but it is thought to be non-migratory, although juveniles (<50 mm LCF) may make upstream movements judging from captures in December in a fishway on Seven Creeks in VIC. Dispersal ability is good, with prolonged swimming capacity, an important trait when living in ephemeral creeks.
Diet is unknown but likely to consist of drifting and benthic aquatic invertebrates taken in pools. Obscure galaxias appear to be relatively tolerant of high turbidity and salinity and high loads of organic leachates from Eucalyptus leaves.
Like many other galaxias species, the Obscure galaxias is often found with small grey to black cysts visible in the flesh, and these are usually the metacercariae of trematode parasites.
The species is one of two widely distributed species within the Mountain galaxias complex (along with Mountain galaxias itself). It is recorded from 0–600 m elevation, is widespread and common throughout its range and can be very abundant in swamps, billabongs and isolated pools.
In the MDB it is widely distributed in the southern tributaries of the Murray River, the Wimmera River system, the upper Murray main channel and NSW tributaries. It is also present in several tributaries of the lower Murray draining the eastern Mount Lofty Ranges in SA but is apparently absent from the Murray mainstem from about Barmah downstream to Mannum. It is the only species in the Mountain galaxias complex known from north of the Great Dividing Range in north-west Victoria (Avoca to Wimmera basins) but may overlap with Mountain galaxias in the very upper reaches of the Campaspe and Loddon River system. The species is found with Riffle and Mountain galaxias in north-eastern VIC and south-eastern NSW (Upper Murray basin to Goulburn River system) and with Mountain galaxias in the eastern portion (Murray River catchment) of the Adelaide Hills in SA. It is also present in coastal drainages in the Merri River and Darlot/Fitzroy River systems in western Victoria and the Hindmarsh River in the South Australia Gulf.
A total of 1985 individuals were collected from 12 river valleys in the Sustainable Rivers Audit (2004–2013), with 90% caught in slopes elevational zones. 943 individuals have been collected in the MDB Fish Survey (2014/15–2021/22) across 11 river valleys.
Unlike other galaxiids, interaction with Rainbow and Brown trout and other predatory fish such as Redfin perch is not a major threat to this species, possibly because it is found in the warmer, lowland streams where trout are not commonly found. However, trout impacts may be greater in smaller, foothill to upland streams. Potential threats are loss of riparian vegetation, drought, water extraction, barriers to fish passage, overgrazing and sedimentation as a result of pest animals and bushfires.
Cook et al. 2019; Dexter et al. 2014; McMaster & Bond 2008; Raadik 2011, 2014, 2019c.
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