Study backs polyculture in Zambian tilapia farms

Small-scale farmers in Zambia are often encouraged to cultivate
tilapia in monoculture systems, removing indigenous small fish species from
their ponds. However, the authors of the study aimed to rethink tilapia pond
systems in Zambia as multi-species systems, that can offer a direct source of food
for household consumption rather than farming tilapia as a cash crop.

The study, which was undertaken by scientists from the
University of Stirling’s Institute of Aquaculture and WorldFish, has been recently
published an open-access paper entitled ‘The role of aquaculture and capture
fisheries in meeting food and nutrition security: Testing a nutrition-sensitive
pond polyculture intervention in rural Zambia’ in the scientific journal, Foods.

“Polyculture of small and large fish species in homestead ponds
improves food and nutrition security of households as well as reduces
micronutrient deficiencies, especially in pregnant and lactating women and
children in the first 1000 days of life,” explained co-author Shakuntala Haraksingh
Thilsted, WorldFish’s global lead for nutrition and public health.

“Small fish, consumed whole, including the head, organs and
bones, pack a bigger punch in terms of vitamins, minerals and omega-3 fatty
acids as compared to the fillet of large fish,” added Thilsted, who is also the
2021 World Food Prize Laureate.

Thilsted was the first to examine the nutritional composition of
indigenous small fish species, commonly found and consumed in Bangladesh and
Cambodia. Her research demonstrated that these affordable and locally available
aquatic foods offer life-changing benefits for children’s cognitive development
in the early stages of their life and the nutrition and health of their
mothers.

WorldFish scientists took these lessons to Zambia by working
with smallholder homesteads to stock various micronutrient-rich small fish
species. Indigenous small fish species are commonly found in wetlands, rivers
and streams that farmers use to stock their ponds. Most of the small-scale pond
systems in Zambia naturally attract large quantities of indigenous small fish
species as they swim in and out of the pond inlets and outlets. This presents
an opportunity for fish to be trapped or for farmers to actively stock them
from the wild if they thrive in the ponds.

The authors identified that aquaculture, especially polyculture
systems with indigenous small fish species, has the potential to improve the
nutrient intake of households during closed fishing seasons. Fisheries
management regulations, introduced by the Zambian government to overcome
overfishing, ban the capture or sale of wild fish between December and February
every year. However, these measures drastically reduce the consumption of fish
during these months, leading to lower intakes of key nutrients and essential
fatty acids. This is especially pertinent for people living in parts of Zambia
where fish is their primary source of animal protein.

“While ponds provide an important supply of fish – polyculture
ponds provide a good source of diverse, micronutrient-rich small fish species –
however, the amount of fish from the wild, especially small fish species from
the large lakes that are dried, play a more significant role in people’s
nutrient intake,” said lead author Alexander Kaminski.

“Ultimately, any improvements to aquaculture should not be done
in isolation without considering the more important role of capture fisheries
in providing cheap, micronutrient-rich small fish for vulnerable people,”
elaborated Kaminski, who is a doctoral candidate at the University of Stirling.

The authors urged the conservation of Zambia’s diverse
ecosystems, especially where nutrient-rich indigenous small fish species reside
to achieve food and nutrition security.