News | 16th Aug, 2012

Casanova Cod


Thursday, 16 August 2012
Bridie Smith, The Age

HE KEEPS returning to his lucky love hotel. For four years, fish ecologists have tracked a large Murray cod, which leaves his lake home to keep an annual river rendezvous. 

Dubbed Casanova cod, the middle-aged fish’s river romances have been monitored via an electronic tagging device. 

Be it drought or flood, he makes the pilgrimage with clockwork regularity. 

‘‘ He’s been very consistent,’’ said fish ecologist Jarod Lyon. ‘‘ He did go slightly earlier in drought years when the water temperature was warmer earlier, but otherwise he’s been very reliable.’’ 

Fish ecologists from the Department of Sustainability and Environment’s Arthur Rylah Institute will soon learn if Casanova makes the 160 kilometre round-trip for a fifth year, with his departure from Lake Mulwala due between now and mid-September . While travelling for love is not unusual for the nationally vulnerable species , the distance is considered notable for such a big fish — he weighs about 25 kilograms. 

It is also unusual to have so much data for Murray cod, and researchers are hoping to learn more about the life-cycle of the fish, listed as endangered in Victoria. 

Measuring a metre long and estimated to be about 25 years old, Casanova is believed to use the same spawning site each year. Researchers believe this is near Tarrawingee, on the Ovens River. His river romances last for betweena month and six weeks. 

‘‘ That tells us that it’s a successful spawning spot, and he’s guarding the eggs,’’ Mr Lyon said. 

Female Murray cod lay the eggs, which are then fertilised by the males. It is the males who remain on duty, guarding and fanning the eggs with their fins to keep them free of sediment, until they hatch into larvae 25 days later. 

The 10-centimetre transmitter implanted into his stomach cavity in 2008 records his solo journey from Lake Mulwala, near Yarrawonga, along the Ovens River to Wangaratta. 

Each time Casanova cod passes tracking stations in Bundalong and Wangaratta his whereabouts is recorded. 

The data will not only help ecologists learn more about the fish, which can live to 45 years, but the conditions they need to spawn and survive. 

‘‘ We’ll get information on the different variables in the environment when he moves, such as water flow rates and temperatures,’’ Mr Lyon said. 

He said that while the Ovens River was largely unregulated, the data could be provided to managers of other rivers such as the Murray, Loddon, Campaspe and Goulburn. 

Read our latest blog on the MDBP here here