Stocky galaxias

Identification

A moderate-sized, stocky galaxiid with truncate or slightly forked tail; the tail is approximately the same length or slightly longer than the caudal peduncle. Maximum recorded size is 113 mm (Length to Caudal Fork; LCF) and 14.3 g, commonly 65–90 mm LCF. The body is a dark olive-brown on the back and upper sides, becoming lighter brown to cream ventrally. The dorsal surface (head and back) is overlain with dark brown to almost black spots that often combine to form irregularly-shaped dark bands or blotches, extending onto the upper sides. The species can be distinguished from the similar Mountain galaxias by the presence of spotting that extends onto the top of the head, cheeks, and jaws. The head is blunt, moderately deep, and slightly bulbous and the mouth is wide and reaches back to below middle of eyes. The anal fin is longer than the dorsal, and usually commences ~3/4 along the length of the dorsal.

Biology and Habitat

Previously confused with Mountain galaxias the Stocky galaxias, was only described as a separate species in 2014, and its ecology is still being described. However, many aspects are likely to be similar to other members of the Mountain galaxias complex. Stocky galaxias occur in two small, (~0.5 - 0.8 m average width and 0.1 - 0.3m in average depth), cold, clear and fast flowing sub-alpine creeks, flowing through open forests of Eucalypts, low shrubs and tussock grass (Tantangara Creek) or open tussock grassland (Sallys Flat Creek). Both streams are often snow-covered during winter. Instream cover consists predominantly of rock, undercut banks and overhanging vegetation (Tantangara Ck) or aquatic vegetation and undercuts (Sallys Flat Creek).

Spawning occurs in mid-November with males maturing much earlier (March/April) than females (October) and at smaller size (males 52 mm; females 70 mm LCF). Males are thought to mature in their second year, with females in their second or third. Fecundity ranges from 210 eggs in a 76 mm LCF fish to 810 eggs in a 100 mm fish. The only spawning site found to date was in late November with most females spent by this time. The egg mass was attached to the underside of a small cobble at the head of a riffle and contained only ~50 eggs, indicating that females may use multiple spawning sites. Eggs are spherical, 1.7-2.2 mm diam. before being spawned. Larvae were detected in December. Spawning cues are unknown, but spawning occurred when mean daily water temperature was ~10°C. Incubation time is unknown but is likely longer than recorded for other species of the Mountain galaxias complex which occur at lower, warmer elevations. Attempts to hold and breed the species in captivity revealed considerable intraspecific aggression leading to mortality of aquarium-held individuals. The species is non-migratory with a very limited home range (≤ 5.5 or 16m for 50% and 75% of fish respectively). Diet is unknown, but likely to consist of drifting and benthic aquatic invertebrates. For Mountain galaxias, up to 20% of the diet comes from insect fall from fringing riparian vegetation, and this also may be the case for Stocky galaxias.

Distribution and Abundance

As a newly described species with few museum specimens, the historical distribution of Stocky galaxias in NSW is largely unknown but was thought to have been confined to the upper Murrumbidgee catchment near the present Tantangara Dam. Until 2021 it was only known from ~3 km of a single stream (Tantangara Creek) at 1,360 – 1,463 m ASL in the NSW Snowy Mountains. In 2021 the species was found serendipitously in another small stream (Sallys Flat Creek) in the nearby headwaters of the Goodradigbee River. It only occurs in around 2.5 km of this stream above a waterfall at ~1,330 m. The species was almost certainly much more widespread before trout were introduced and is now restricted to habitats upstream of substantial waterfalls that exclude trout. In Tantangara Creek it is the only fish species present but at Sallys Flat Creek the closely related Mountain galaxias occurs with no evidence of hybridisation between the two. The species is not known from outside NSW. No individuals have been recorded from the Sustainable Rivers Audit (SRA) (2004–2013) or the MDB Fish Survey (2014/15–2021/22). The species was not yet formally described during the term of the SRA.

Potential Threats

Most threats are exacerbated by the species’ extremely limited distribution. Interaction with Rainbow and Brown trout (largely predation) is the major threat. Other threats include loss of riparian vegetation, overgrazing and sedimentation as a result of pest animals and bushfires. Feral horses damage instream habitat via sedimentation at stream crossings, riparian damage, and alteration of stream width, depth and substrate. The Snowy 2.0 pumped hydro scheme has the potential to introduce a non-native Galaxias (Climbing Galaxias) which will likely compete with and prey upon Stocky galaxias. The waterfalls that protect Stocky galaxias from trout will be ineffective at excluding Climbing galaxias. Severe drought could cause drying of the stream and loss of the species. Potential egg predation from the invasive Oriental weatherloach is also a threat with this species spreading throughout the upper Murrumbidgee catchment via its illegal use as live bait. Climate change will likely increase air and water temperature, alter snowmelt and stream flow patterns, increase the frequency and intensity of storms and floods, and the frequency, extent and severity of drought and bushfires. 142 Stocky galaxias were rescued from Tantangara Creek as the catchment began to burn in the 2019-20 fires.

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General References

Allan et al. 2018; 2021, 2022; Allan & Lintermans 2021; Driscoll et al. 2019; Lavery et al. 2022; Lintermans 2019, 2020, 2022a; Lintermans & Allan 2019; Lintermans et al. 2008b, 2020, 2021; NSW FSC 2016; Raadik 2011, 2014; Scanes et al. 2021; Shelley et al. 2021; TSSC 2021; Zukowski et al. 2021; H. Allan unpubl. data; M. Lintermans unpubl. data.

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See complete reference list