700kg of dead fish pulled from lake
UNUSUALLY cold water temperatures in the Forest Lake catchment have been blamed for a major kill off of noxious fish, with council clean-up crews taking 700kg of dead tilapia away in the past week.
While daytime temperatures were warm in July, colder nights in the catchment have sent lakewater temperatures plummeting to below the point at which the invasive African species can survive, according to the Brisbane City Council.
The result has been a spectacular kill off, with lake resident Nicole Whysall's photographs, shown here, telling the smelly tale.
Ms Whysall said she there was little sympathy for these fish, as they were noxious and invasive.
Brisbane City councillor (Forest Lake) Charles Strunk said the species was believed to have arrived in Queensland waterways after being released from home aquariums.
Tilapia is regarded as an important food fish in African countries, but is a pest in Australian waters.
"The council team has taken 700kg of dead fish out of the water so far," he said.
"There were no other species involved.
"These fish feed at the bottom and can cope quite well with lower levels of oxygen but can't stand the cold, which our native fish and eels tolerate better.
"There was a similar kill off of the tilapia after cold weather in 2008, but not much since."
Cr Strunk said the clean up would continue regularly until it was no longer required.
He said the tilapia were well established in the lake and able to survive lower-oxygen levels created when water was contaminated by excess algae levels.
Cr Strunk said the council had tested the water at nine points this week and it had returned to reasonable algae levels after a concerning high in May.
He blames overuse of fertilisers for much of the problem.
But, the dead tilapia fish had provided a bounty for the pelicans and other birds this week and were safe for them to eat, he said.
"There is no poisoning, as such, and the water algae levels have returned to a reasonable level," he said.
Cr Strunk said the council was considering a biocontrol plan to help reduce algae levels by introducing lillypads into shoal areas that would compete for the same food source as the algae.
Ms Whysall and her husband take an interest in pest fish species and have a website called Pest Fishing Adventures and a facebook page with more photos