SPAWNING OF THE MOUNTAIN GALAXIAS, GALAXIAS OLID US GUNTHER, 
IN BRUCES CREEK, VICTORIA 
W. G. O’Connor and J. D. Koehn 
Freshwater Ecology Branch, Department of Conservation and Environment, 
123 Brown Street, Heidelberg, Victoria 3084 
O’Connor, W. G. & Koehn, J. D.. 1991:12:31. Spawning of the mountain galaxias, 
Galaxias olidus Gunther, in Bruces Creek, Victoria. Proceedings of the Roval Society of 
Victoria 103 (2): 113-123. ISSN 0035-9211. 
In Bruces Creek, Victoria, Galaxias olidus had a spawning season extending from early 
August to late October. Water temperatures ranged between 8° and 10.2°C over this period. 
Fertilized eggs were mainly found attached to the underside of boulders in rifiles but some 
eggs were also found lodged amongst substrate or drifting downstream. G . olidus had a 
relatively low fecundity with an average of 198 eggs per female. Average egg diameter was 
2.3 mm. All G. olidus were mature in their second year, although males matured earlier than 
females. The population had an overall sex ratio of 1:1 but the sexes were unevenly dis¬ 
tributed. with more males in 0+ and more females in 2+ and 3+ year classes. The 
preferred habitat of adults was in pools. Fertilized eggs collected from the stream at an early 
stage of embryonic development hatched in the laboratory' after 21 days at temperatures 
between 12.9° and 14.8°C. Newly hatched larvae averaged 9.4 mm in length. 
THE MOUNTAIN GALAXIAS, Galaxias oli- 
dus Gunther, a small (less than 145 mm long) 
native freshwater fish of the family Galaxiidae 
(McDowall 1980a), is generally found in small, 
headwater streams (Berra 1973, Fletcher 1979, 
Jackson 1981) at altitudes up to 1800 m 
(McDowall & Frankenberg 1981). The species 
occurs from southern Queensland to south¬ 
eastern South Australia (Merrick & Schmida 
1984), although it has been recognized as having 
a highly fragmented distribution, often occur¬ 
ring in small isolated populations (Tilzey 1976, 
Cadwallader 1979, Jackson & Davies 1983, 
Cowden 1988). 
G. olidus is widespread throughout Victoria 
(Cadwallader & Backhouse 1983), where its con¬ 
servation status is “indeterminate” (Koehn & 
‘ Onson 1990) due to uncertainty about the 
taxonomic status of the various taxa in this 
species complex. The population of this complex 
occurring in Bruces Creek conforms to the “typi- 
olidus form (see Cadwallader & Back- 
ou $e 1983). Although most of this taxon is 
common and widespread, G. olidus var. fuscus 
as been categorized as endangered in Victoria 
son 199^ Morison 1990) and nati onally (Jack- 
Until recently there had been little investi¬ 
gation of the life history of G. olidus (Koehn & 
°Kr°u * 999a )- M° s t information remains 
unpublished in university theses (Harasymiw 
q£ Tu tCher 1979 ’ Cowden 1988, Drayson 
'■ Ihe present paper contains information 
on the spawning of G. olidus in a small Victorian 
stream and includes data on habitat, population 
structure, sexual maturity, fecundity, spawning 
season and site, egg description, incubation 
period, and description of larvae. 
STUDY SITE 
The study was conducted in the upper reaches of 
Bruces Creek, Victoria, approximately 47 km 
north-east of Melbourne (Fig. 1), where 
McKenzie & O’Connor (1989) found a large 
population of G. olidus , the only fish species 
present. The absence of other species, particu¬ 
larly predatory species such as brown trout, 
Salmo trutta , was considered important as it 
allowed instream distribution and habitat pref¬ 
erences to be unaffected. S. trutta has been 
implicated in the displacement of Galaxias oli¬ 
dus, G. truttaceus and G. brevipinnis from pre¬ 
ferred habitat areas (Koehn unpubl. data). 
Bruces Creek rises on the western slopes of Mt 
Disappointment in the Great Dividing Range 
and flows firstly in a southwesterly then south¬ 
easterly direction to its confluence with the 
Plenty River. The study site was about 6.5 km 
downstream from the source of Bruces Creek at 
an altitude of 340 m. At the site, Bruces Creek is 
a small, shallow, third order stream with an aver¬ 
age width of 2.0 m, an average depth of approxi¬ 
mately 0.3, and consisting of alternating pools 
and riffles. The stream is in a relatively natural 
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