Dar es Salaam. Tanzania is home to over 20 tilapia varieties including some rare species.
However, increasing fish farming that involves interbreeding is threatening the fish species that have made Tanzania one of the global hotspots.
Crossbreeding native varieties with non-native ones can lead to contamination, according to new research findings by Tanzanian and British institutions.
The research was led by Prof George Turner of Bangor University, in collaboration with colleagues at Bristol University and at the Tanzania Fisheries Research Institute (Tafiri).
The seven-year research programme which mapped the distribution of native and non-native tilapia varieties shows that introduced species threaten Tanzania’s fisheries.
“Tilapia Lake Virus, for example can wipe out up to 90 per cent of fish stocks and has an annual economic impact of $100 million in Egypt alone,” it states.
“We found evidence of cross-breeding in both fish farms [aquaculture] and the wild [capture fisheries] and revealed contamination of both systems with highly invasive small-bodied tilapia. This genetic mixing could lead to reduced fisheries harvests and threaten the sustainable aquaculture development needed to keep pace with population growth,” it reads.
Tilapia is a group of large-bodied freshwater fish found across Africa, and now widely farmed in tropical and subtropical regions of the globe.
In Tanzania’s small-scale rural fish farms, brood-fish are often sourced from stocks contaminated with less productive species, according to the study. Fish ponds are also seasonally connected to natural water bodies, allowing farmed and local species to mix and transfer disease.
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.
In Tanzania, total fisheries production is estimated at an average of 370,000 tonnes annually.
The recommendations of the research were delivered to Ministry of Livestock and Fisheries.
“We are working on them,” the ministry’s permanent secretary, Dr Rashid Tamatamah, told BusinessWeek. “I call upon all aquaculture stakeholders to be careful and ensure that they apply techniques and measures which will preserve the species. The aim is to increase productivity.”
Nile tilapia is said to be the mainstay of the $10 billion global tilapia industry, and Tanzania is a global hotspot for its wild relatives.
Between 2011 and 2017, researchers 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.
It was found that 54 per cent of (67 of the 123) sampling locations contained one or more invasive species. Native species persisted without introduced species in 56 sites (46 per cent) and many of these sites could be used to establish ark populations for tilapia conservation.
Experts say interbreeding is increasingly having negative consequences on both productivity and food security. “The results underline the need for aquaculture and capture fisheries policies to protect natural biodiversity and harness its valuable role in promoting food security,” says Prof Martin Genner, one of the researchers from the UK’s University of Bristol in his emailed response to Business Week.
“In a country facing rapid population growth, a reduction in fish production as a food source poses a serious threat to the sustainable aquaculture development needed to keep pace with population growth,” he added. Hybridisation between native and non-native tilapia species has been recorded at multiple sites in Tanzanian lakes, rivers, fish farm ponds and national hatcheries used to distribute broodstock.
The research also indicates that 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. n“This is a challenge that requires immediate action,” says Dr Benjamin Ngatunga of Tafiri, in an interview.
He said the distribution of hatchery-validated juvenile fish need to be enhanced to avoid contamination with small-bodied invasive and zoned aquaculture for smallholders and should be based on species indigenous to the catchment.