J. D. KOEHN AND T. A. RAADIK 
substrate and vegetation from the site. The be¬ 
haviour and position of the fish were observed at 
intervals throughout each day for three weeks, 
and at 5 minute intervals for 1 hour during one 
night. 
Generally the fish were inactive during the 
day, resting either on the substrate or amongst 
vegetation, and were difficult to locate because 
of their colour and cryptic habit. Individuals 
spent time resting either on the substrate 
wherever cover was available, or amongst dense 
weed just below the water surface. In both situ¬ 
ations, several individuals shared the same 
cover and were in physical contact with each 
other. This behaviour is similar to that described 
by Eldon (1969) in Neochanna apoda which is 
also territorial and aggressive to other species in 
aquaria (Eldon 1968). Individuals of G. cleaveri 
exhibited no such aggressive behaviour to each 
other or to individuals of Galaxias maculatus or 
G. truttaceus which were placed into the aquaria 
at different times. At night G. cleaveri were more 
active, continually moving around open areas 
“browsing”. At least two of the fish were in open 
areas at each observation. They immediately re¬ 
treated into the vegetation when exposed to 
either white or red light but had always re¬ 
appeared in the unvegetated areas by the next 
observation. 
Our observations indicate that G. cleaveri is a 
nocturnal, cryptic species which often inhabits 
the aquatic vegetation rather than the substrate. 
Other species of galaxiids reported to be noctur¬ 
nal are Neochanna apoda (Eldon 1968), Gal¬ 
axias brevipinnis (Glova & Sagar 1989a), and 
Galaxias vulgaris Stokell (Glova & Sagar 
1989b). 
AESTIVATION 
Scott (1934) gave details of the ability of G. 
cleaveri to aestivate, though under unnatural 
conditions. This ability has been noted by sev¬ 
eral other authors (Fletcher 1907, Hall 1901, 
Fulton 1986) though their descriptions mainly 
concern recovery of aestivating individuals. Ful¬ 
ton (1986) provided photographic evidence of 
G. cleaveri aestivating during mid-summer 
under a rock at least 10 m from free water. 
McDowall & Pusey (1983) reported aestiv¬ 
ation in Lepidogalaxias salamandroides , and 
aestivation of Galaxiella pusilla was suggested 
by McDowall & Frankenberg (1981). Humph¬ 
ries (1985) tested this suggestion by maintaining 
specimens of G. pusilla in an aquarium for 36 
days whilst lowering water levels and maintain¬ 
ing oxygen concentrations at less than 5 ppm. 
Fish survived on the surface of the mud and in a 
small hole for several days in the absence of 
surface water. McDowall (1990) presented evi¬ 
dence of the ability of the New Zealand mud¬ 
fishes Neochanna burromius and N . apoda to 
survive dry periods, though both Eldon (1978) 
and Meredith (1985) concluded that these spe¬ 
cies do not exhibit true aestivation during which 
the individual becomes torpid and the normal 
rate of metabolism decreases. 
We investigated whether burrowing and aesti¬ 
vation could be induced in G , cleaveri by placing 
two individuals (101 mm and 78 mm TL) into a 
glass aquarium (0.3 x 0.62 x 0.3 m) containinga 
substrate of soil and mud, a large flat rock at one 
end, dense aquatic vegetation in the middle, and 
a piece of log at the other end. The water level 
was lowered artificially, and heating and illumi¬ 
nation were provided during the day by an 
incandescent globe. On day 10 some tunnelling 
in the middle section of the tank was observed, 
and one fish was seen lying near the water sur¬ 
face where it spasmodically gulped water and 
air. On day 14, when the water level had fallen to 
10 mm above the substrate, one fish was resting 
in a vertical shaft in the mud with its head just 
protruding. On day 22 neither fish could be seen 
and no surface water remained, though water 
was present in the opening of the shaft. Later on 
the same day the heads of both fish were pos¬ 
itioned in the shaft opening and their bodies 
were under the mud in horizontal tunnels. On 
day 25 a series of smaller openings were ob¬ 
served in a line directed away from the large 
shaft, presumably along the horizontal tunnels. 
On day 31 there was no water in the pit of the 
large shaft, the mud substrate had begun to dry, 
and one G. cleaveri had its head protruding from 
the tunnel into the shaft below the surface of the 
substrate. On day 32, after 5 days without any 
free water, the fish in the tunnels stopped mov¬ 
ing. On day 42 when the substrate had dried to 
only 30 mm thick the two G. cleaveri were seen 
through cracks in the dry mud lying in the tun¬ 
nels. The tank was then slowly rehydrated, and 
the fish recovered movement and emerged when 
the mud became soft. They both immediately 
fed on earthworms and showed no ill effects 
from surviving in stagnant water for 14 days and 
without surface water for another 14 days. 
Whilst not physiologically confirming the 
ability of G. cleaveri to aestivate, our study 
shows that the species can survive periods 
without free surface water by burrowing into the 
substrate. 
