FRESHWATER FISH IN THE OTWAY REGION 
33 
1971). If the small coastal streams to the east of 
the Otway Range had been formed by this time 
they would have been susceptible to droughts 
and may have flowed intermittently. Interrup¬ 
tion to their flow or their complete drying may 
have destroyed the freshwater fish fauna that 
had been present in them before about 770 
BP. 
Evidence that the original fish fauna in these 
streams may have been destroyed in this way is 
to be found in the extant native fish fauna con¬ 
sisting entirely of species which have a marine 
component in their life cycles and which could 
have recolonised from the sea. In contrast, the 
Aire, Gellibrand and Barwon river systems con¬ 
tain four species of native fish which spend their 
entire lives in fresh water. These river systems 
may not have been effected by the land bridge or, 
being much larger, were less influenced by the 
arid conditions. 
The Australian smelt, a small forage species, 
was absent from the coastal streams but has been 
found in the Aire, Barwon and Gellibrand 
Rivers (Hall & Tunbridge 1988, Tunbridge & 
Glenane 1988). Freshwater blackfish are usually 
more abundant in habitats with low water velo¬ 
cities and with logs and wood debris which are 
used for instream cover and for spawning sites 
(Jackson 1978a, 1978b, Koehn 1986d). The 
coastal streams from which this species was 
absent are essentially low order streams that are 
fast- flowing but which commonly contain many 
pools where water velocity is low and wood 
debris present. The freshwater blackfish has 
been recorded in the Aire River system and is 
widespread throughout the Gellibrand and 
Barwon Rivers in similar habitats (Flail & Tun¬ 
bridge 1988, Tunbridge & Glenane 1988). The 
southern pigmy perch is commonly associated 
with aquatic vegetation (Cadwallader 1979), 
with mud substrates (Jackson & Davies 1983), 
and with slow-flowing or still waters (Llewellyn 
1974). Small areas of such habitats are present 
though not common in the Otway coastal 
streams, but southern pigmy perch were absent. 
The species has been recorded from the 
Gellibrand and Barwon River systems (Hall & 
Tunbridge 1988, Tunbridge & Glenane 1988). 
Mountain galaxias were also absent from the 
coastal streams but were collected from tributar¬ 
ies of the Gellibrand and Barwon Rivers in habi¬ 
tats similar to those found in the Otway coastal 
streams. The absence of the mountain galaxias 
from the coastal streams cannot be attributed to 
the presence of large numbers of brown trout, 
which are known to exclude mountain galaxias 
(Tilzey 1976, Cadwallader 1979, Fletcher 1979, 
Jackson & Davies 1983), because the latter were 
collected from tributaries of the Gellibrand and 
Barwon Rivers where trout were widespread. 
The presence of mountain galaxias in the 
Parker River and of freshwater blackfish, moun¬ 
tain galaxias and Australian smelt in the Aire 
River system delineates the boundary where fish 
distribution changes (Fig. 1). Although it is sim¬ 
ilar in size to other Otway coastal streams, the 
Parker River in the middle of Cape Otway may 
not have been subjected to the same geomorpho- 
logical conditions as streams farther to the 
east. 
The fish fauna in the Otway coastal streams is 
similar to that in the short coastal streams 
flowing east from the Mornington Peninsular 
ridge (Koehn 1986b), which may have been sub¬ 
jected to similar geomorphological and climatic 
conditions as the Otway region. 
There are marked similarities between the 
native freshwater fish fauna of the Otway region 
and Tasmania, most species being common to 
these areas. The distribution of species whose 
life cycle is spent entirely in freshwater is es¬ 
pecially interesting. In Tasmania, the southern 
pigmy perch, Nannoperca australis , and fresh¬ 
water blackfish, Gadopsis marmoratus , occur 
naturally only in northern rivers flowing into 
Bass Strait (Frankenberg 1974). The Gadop- 
sidae appears to be an entirely freshwater family 
that is restricted by salt-barriers. It has been sug¬ 
gested that the severe reduction or obliteration 
of freshwater streams on the Bass Strait islands 
during glaciation may have resulted in the 
extinction of Gadopsis from this region (Sanger 
1986). 
The dwarf galaxias, Galaxiella pusilla , was not 
found in our study area but it is present in 
western Victoria (Tunbridge & Glenane 1983). 
Populations of this species are also found on the 
north coast of Tasmania and on Flinders Island 
(Frankenberg 1974). 
Frankenberg (1974) suggested that the 
freshwater blackfish, southern pigmy perch and 
dwarf galaxias migrated to Tasmania from the 
mainland when the landbridge existed and when 
continuities of fresh water were likely. In con¬ 
trast, Sanger (1986), on the basis of work by 
Watson & Littlejohn (1985), favoured a 
northward dispersal of the freshwater blackfish 
from Tasmania. Frankenberg (1974) also sug¬ 
gested that the spotted and broad-finned galax¬ 
ias may have migrated to the mainland from 
Tasmania during the same period. However, the 
occurrence of larval galaxiids as much as 700 km 
