Why is sustainable fisheries production important?

• In Tanzania, total fisheries production has plateaued at approx. 370,000 tonnes per year.

• Tanzania’s population is expected to rise from 53 million in 2015 to 138 million by 2050. Current aquaculture production will not meet the expected demand.

• Globally, aquaculture has been expanding as wild fisheries have reached maximum capacity.

• Tanzania has substantial scope to build aquaculture development by applying modern technologies, a strategy employed by Egypt - the largest producer of aquaculture products in Africa.

Fisheries production in Tanzania, and globally (data sourced from FAO 2018)

Tilapia are a group of large-bodied freshwater fishes found across Africa, and now widely farmed in tropical and subtropical regions of the globe.

Nile tilapia is the focus of most aquaculture development in Tanzania and the world. It can generate extremely high yields when farmed in optimum conditions, but relying on a single species with low genetic diversity is risky in the face of disease outbreaks.

Even occasional contamination of high-intensity systems can lead to catastrophic losses.

Global tilapia production would benefit from disease-tolerant strains developed using wild relatives, such as those in Tanzania.

In small-scale rural fish farms in Tanzania, broodstock are often sourced from stocks contaminated with less productive species.

Ponds connect seasonally to natural waterbodies, allowing farmed and local species to mix and transfer disease. Uncontrolled breeding leads to inbreeding and accidentally promotes production of small early maturing fish.

Rural aquaculture could benefit from “zoned aquaculture”, where ponds are stocked with large-bodied local native species.

This strategy uses stocks adapted to local climate and pathogens, and genetic diversity of hatchery strains can be maintained by periodically refreshing broodstock from local waters.

Many attempts to improve fisheries productivity of inland lakes have introduced non-native species, without investigating the existing species composition, regional demand for fish, or the water’s maximum productivity.

Non-native species in Tanzania: prevalence and impacts

Between 2011 and 2017 we sampled 123 freshwater sites across all major catchments in Tanzania.

• Fourteen species were restricted to their native range, and three species had been introduced beyond their native range.
• Non-native Nile tilapia were found in all major catchments in the country, while the Singida tilapia and Blue-spotted tilapia were also extremely widespread.
• Most sampling locations contained one or more invasive species (67 of 123, 54%).
• Native species persisted without introduced species in almost half the sites (56 of 123, 46%). Many of these sites could be used to establish ark populations for tilapia conservation.

Our results revise the distribution of indigenous species in Tanzania, providing an evidence base for zoned aquaculture.

Across all sites sampled in Tanzania (left) introduced species were common (right) 

Positive findings

• The IUCN “Critically Endangered” Jipe tilapia supports many successful fisheries across the Pangani system.
• The IUCN “Vulnerable” Rukwa tilapia supports a highly productive tilapia fishery in the Mtera Dam on the Upper Ruaha
river system.

Negative findings

• Hybridisation between native and non-native tilapia species has been recorded at multiple sites in Tanzania; lakes, rivers,
fish farm ponds and national hatcheries used to distribute broodstock.
• Blue-spotted tilapia is hybridising with the larger species preferred in wild fisheries and aquaculture. This is expected to
lead to declines in body size and profitability of populations in both systems.

Key findings

• Tanzania contains a rich diversity of indigenous tilapia species, many of which have potential as target species within a zoned aquaculture strategy for aquaculture smallholders.

• The native species, and future fish production, of Tanzania are potentially threatened by non-native species that are now broadly distributed across the country.

• There is evidence that several productive fisheries are being supported by critically endangered and vulnerable native species.

• Our surveys allow these ark populations of native species to be identified and protected, enabling their genetic diversity to help with strain improvement that will help commercial aquaculture expand.

• Capacity to reliably identify tilapiine species should be improved among researchers and stakeholders in Tanzania, to improve prospects for sustainable aquatic resource management.