The day after the
2018 March deluge stopped, the local stormwater drain was full of
fish. Not just any fish but strikingly colourful fish. These fish
had come to spawn. They are all native fish that are usually brown,
but on this day they were dressed up to impress. Two species were
putting on a show, snakehead gudgeons and empire gudgeons. Snakehead
gudgeons, not to be confused with Asian snakeheads or fishzilla, are
a native Australian fish of mangrove estuaries.
The females were fat with eggs and males where brightly coloured (click to zoom)
A pale snakehead with bright ventral fins
The snakeheads
gudgeons slowly circled in the main pool with males showing their
colour to the females. There were two males and each time one made a
move toward the girls, the other would approach and swim beside the
first male to make sure that the girls knew he was there too. I did
not see any fighting and the boys sometimes followed the girls and
vice-versa. It was speed dating in slow motion and eventually the
girls decided who was best.
Two males trying to entice a female to their corner of the pond
Around the edges of
the pool were bright red male empire gudgeons. At about 8 cm long,
they were so full of confidence, that they were even approaching the
25 cm long snakehead gudgeons, which annoyingly had large patches of
red. By the afternoon the empire gudgeons were gone, probably having
expended themselves, they had ceased displaying. Their colours would have
back to mostly brown although the keep their red head.
Male empire gudgeon displaying on wall of drain
Surprisingly, the
drain was almost empty before the deluge. Only a few rainbow fish
(Melanotaenia splendida)
had colonised since the wet reestablished a persistent pool at the
outlet of the drain. In dry years, the drain can be dry for most of
the year. During the wettest years, it can flow for most of the year
and can support a diverse freshwater fish community of a dozen
species. Being above normal tidal limits, the water within the drain
is completely fresh, unless an extreme tide pushes in. Paperbarks
and beach hibiscus line the drain and the beach hibiscus have grown
long trailing roots into the flowing water, which now form a thick
mat that the migrating fish have to negotiate.
Hibiscus tiliaceus creates deep root mats in flowing freshwater
Female snakehead gudgeon resting in the root mat
The drain is
somewhat special. It is near the mouth of a river, so when the
juveniles of freshwater fish are flushed out by floods, they often
attempt to swim up the drain. Originally, before development, there
was supposed to have been a drainage line in much the same position.
Small creeks and drainage lines would once have been common but now
have been replaced by farm drains and urban drains. There are not
many small intact waterways which flow during the wet but dry out and
prevent common freshwater fish such as guppies, tilapia and even
native jungle perch from dominating the ecosystem. Perhaps this
explains the desire for the gudgeons to breed in this waterway.
Pool where water leaves concrete drain
25 metres below where the drain emerges,the freshwater flow fans out in a mangrove swamp
In the late
afternoon, I decided to put my underwater compact camera on a pole
and push it below the surface to see if I could get some close up
photos. As I can’t clearly see what the camera is shooting, I use
video, then create stills from the video. It was almost
unbelievable, what the camera recorded. The fish were in the process
of spawning when videoed.
The next day, I went
back to try and get some new shots and the fish were largely gone.
Only two or three snakehead gudgeon were present and they were much
more wary of people and darted for cover. Males of both species were
loitering and hoping for late females, but had lost most of their
colour and enthusiasm. They only consolation was that I was able to
photograph the very tiny eggs (white specs) that had been glued on dead wood the
day before. The video clip shows these very eggs being deposited. Firstly the female glues them to something with the pink appendage and then the male fertilises them (not visible in this clip) using a similar pink appendage.
Tiny white eggs deposited on a stick
Whilst I have called
the fish snakehead gudgeons, I am not totally sure as they were
identified using photos from the net. Usually, spangled gudgeons (Ophiocara porocephala) are
the main local species and are of similar size and shape. So few
photos of the fish in their breeding colours are on the net, that
positive identification is difficult. Usually, it is best to review several
sources, particularly authoritative sources before labeling species.
