"We don't know yet what will happen to the ecosystem. It is an omnivore and eats detritus, rotting vegetation, dead fish, the eggs of bream and other aquatic life as well as all the organisms that are crucial in the whole ecological chain," he said.
Nor is it known exactly how many crayfish are in Kariba lake. Phiri says they are most visible breeding unchecked close to human settlements, harbors and slipways for boats. Kariba's "kapenta" fish, a tiny tropical whitebait or sardine that has become a staple food, was also introduced into the lake but does not migrate because it only lives in deep water lake conditions.
The red claw from Australia was first "farmed" in neighboring Zambia but has already found its way deep into that country's lake tributaries where its worrying impact is also being urgently tracked.
The solution to the crayfish crisis, said Phiri, seems to lie in commercial exploitation in traps similar to those used to catch marine lobster.
In stores in Harare, it sells for $9 a kilogram (2.2 pounds), $12 still alive in fish shop aquariums, and far more in upmarket restaurants patronized by the wealthy well-traveled elite and Zimbabwe's growing Chinese community.
Phiri said impoverished villagers capture the red claw and relocate to water closer to urban markets in central Zimbabwe.
Neighboring South Africa has banned commercial operations and breeding of the still water crustacean in Argentina, Mexico and Australia is strictly controlled for environmental reasons.
"We don't have the resources on the ground to license or police exploitation on the right scale at Kariba," said Phiri. "The important thing is we don't want people to introduce it elsewhere."