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Sifelani Tsiko, Innovations Editor

The invasive crayfish species is among the leading threats to the survival of the tilapia fish on Lake Kariba and many of the country’s major internal dams and lakes.

Rising crayfish populations could threaten or endanger local fish species and damage the country’s fisheries sector.

It is also posing risks to human health, food security and livelihoods of fishing communities dotted along the Zambezi river as well as other water bodies inside the country.

According to the University of Zimbabwe marine biologists, the impacts of invasive species such as crayfish on the country’s water bodies and natural ecosystems could cost the economy thousands of dollars each year.

The marine biologists said many of the country’s commercial, agricultural, recreational activities and the livelihoods of local communities depend on healthy native ecosystems which offer conducive environments for the tilapia fish to thrive.

Now, even though invasive species such as crayfish may sound threatening due to their devastating effects on other important marine resources, UZ researchers have come up with one way to curb the spread of this invasive species.

“The invasive crayfish species is spreading aggressively in Zimbabwe’s water ecosystems posing a huge threat to other marine species. I am leading a team of UZ researchers to find resource-use strategies to manage crayfish  and reduce their effect on other species,” said Dr Takudzwa Madzivanzira, a UZ Department of Biological Sciences and Ecology lead researcher.

“Our fresh water research group is doing research on crayfish that is invasive and spreading in our fresh water systems here in Zimbabwe. We have since established that it is present in Lake Kariba, Mazvikadei and other water bodies.

“This crayfish is invasive, it affects other biotic organisms, fish, macroinvertebrates, insects, plants. So of major concern is how it affects the fisheries industry.”

The UZ researchers have worked out an adaptive management strategy that involves harvesting the crayfish tails just like other edible crabs for both the local and export market.

Ecologists say invasive plant species are characterised by fast growth rates, short life   cycles, higher reproductive potential, high competitive abilities and allelopathy that make them successful invaders of native habitats.

The main key characteristic of an invasive plant is that it is not indigenous to the area and it tends to spread rapidly and overpower the local indigenous plants.

“Invasive species cause harm to other species in many ways. When a new and aggressive species is introduced into an ecosystem, it may not have any natural predators or controls. It can breed and spread quickly, taking over an area,” said Dr Madzivanzira.

“The crayfish, for instance, attacks the tilapia fish and other marine species which cannot compete with them. It has no predators.”

Ultimately, he said, crayfish can prey on native species, outcompeting native species for food or other resources, causing or carrying diseases and preventing native species from reproducing.

“When fishermen lay their nets, the crayfish comes on the nets and starts nibbling on the fish caught on the gill nets. They cause damage to tilapia fish and this is of concern to us. So what we are saying is that let us create value out of this crayfish and a market for it. Let us harvest, take them out of the lake and create value out of them,” the UZ marine ecologist said.

“So we now harvest them, taking their tails which we are going to be marketing. We are currently determining the protein level in the tails and also their food safety levels in terms of presence of heavy metals.

“When we do the analysis, we can then recommend harvesting to our local communities knowing very well their protein content levels and safety.”

Reports indicate that fresh water crayfish was brought from Australia and introduced for a fish farming project on Lake Kariba around the 2000s.

After its introduction, it bred out of control voraciously feeding on food sources of other fish and marine species.

This posed serious risks for the Lake Kariba aquatic ecosystem.

Crayfish populations have grown infesting rivers, dams and other water bodies in Zimbabwe.

This invasive species devours everything from rotting vegetation, anything organic to other microorganisms that other marine species also need.

Crayfish has high protein content, but it is not a popular delicacy for many Zimbabweans, leaving those who may want to harness it, with the export option.

Dr Madzivanzira said the commercial exploitation of crayfish may help by “Turning a curse into a blessing through utilisation of invasive crayfish in Zimbabwe.”

He said there is a potential to sell 500g of crayfish tails for prices ranging between US$5 and US$8 in some upmarket restaurants in Harare patronised by a growing Asian community.

Selling live crayfish to some fish shop aquariums could be another potential area to help manage the invasive species.

With proper strategies and adequate resources, it is possible for the country to take a dive into the global market and tap into the rising demand for marine food supported by a changing preference of consumers.

According to the UN Food and Agriculture Organisation (FAO), 40 million more tonnes of seafood, or a nearly 30 percent increase, will be needed to meet rising demand by 2030.

Additionally, an increase in disposable income of the people is also predicted to increase the growth of the crayfish market during the forecast period 2021 – 2026.