Fish spawning in the big wet

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.

Spangled gudgeon usually hunt around this area.