The research, conducted by Boniface Daka, Tongayi Mwedzi, Beaven Utete, Panashe Mataranyika and Taurai Bere of the Department of Freshwater and Fishery Sciences at Chinhoyi University of Technology, and published in the journal Discover Sustainability, set out to test a hypothesis with direct relevance to small-scale farmers. The team proposed that partially replacing fishmeal with Azolla pinnata would maintain acceptable growth performance in Nile tilapia, Oreochromis niloticus, while proving cost effective at the level of a small aquaculture operation. Nile tilapia is one of the most widely farmed fish in Africa and a cornerstone of food security efforts, making it an ideal test case for a feed innovation aimed at advancing Sustainable Development Goal 2, which targets the end of hunger, food security, improved nutrition and sustainable agriculture.

Azolla pinnata is a remarkable plant in its own right. This tiny fern floats on the surface of still water and harbours a symbiotic cyanobacterium in its leaves, allowing it to fix atmospheric nitrogen and accumulate protein at levels that make it genuinely interesting as a livestock and fish feed. It grows rapidly, requires no arable land, and thrives in the same kind of ponds that tilapia farmers already manage, which means a farmer could theoretically cultivate feed and fish side by side. That combination of rapid growth, local availability and protein content has made Azolla a recurring candidate in the search for alternative aquafeed ingredients across Asia and Africa.

The experimental design was straightforward but rigorous. The researchers formulated three diets matched to approximately similar crude protein levels of around 36 percent, the standard target for tilapia grow-out feeds. One diet was a conventional commercial fishmeal-based feed, serving as the control. The other two contained Azolla pinnata at inclusion levels of 10 percent and 15 percent, replacing a corresponding portion of the fishmeal. Each treatment was replicated across triplicate ponds, and the fish were fed for 91 days, a period long enough to capture meaningful growth trajectories. Water quality parameters were monitored throughout, and statistical analysis of variance found no significant differences among treatments, an important control that ensured any growth differences could be attributed to diet rather than to the pond environment.

Proximate analyses of the feeds revealed a detail that matters for interpretation: the commercial feed and the 15 percent Azolla inclusion diet had similar overall composition, meaning the comparison at that level was as close to a like-for-like test as feed formulation allows. The fish were then weighed and their growth tracked over time, with the researchers examining not just final weight gain but the temporal patterns of specific growth rate, a metric that expresses how quickly fish grow relative to their body mass and reveals whether growth advantages or deficits emerge early or accumulate over the culture period.

The results told a nuanced story. Fish fed the commercial fishmeal-based diet attained significantly higher weight gain and specific growth rates, and achieved lower feed conversion ratios, meaning they needed less feed to put on each unit of body weight. In statistical terms, these differences were significant at the p less than 0.05 level. In practical terms, Azolla-fed tilapia still grew, and grew acceptably, but they did not match the performance of fish on the full commercial diet. The researchers therefore concluded that Azolla pinnata is best understood as a complementary protein ingredient rather than a complete replacement for fishmeal in Nile tilapia diets. The plant can carry part of the protein load, but the data suggest that pushing inclusion beyond a certain threshold begins to compromise the growth economics that fish farming depends on.

That threshold, according to the study, sits at roughly 15 to 20 percent Azolla-based partial replacement of commercial feed. Within that window, the economics become compelling. The researchers calculated that using this optimised partial replacement level could yield savings in the region of 500 to 700 US dollars on feed costs within the first 18 to 24 weeks of pond aquaculture production. For a small-scale farm in Zimbabwe or a comparable setting, that is not a rounding error; feed routinely accounts for the majority of operating costs in aquaculture, and savings of that magnitude can determine whether a venture is profitable at all. The finding reframes Azolla not as a miracle ingredient but as a pragmatic lever for farm-level sustainability.

The implications extend beyond a single farm budget. Fishmeal production depends on catching vast quantities of small pelagic fish such as anchovies and sardines, species that also underpin marine food webs and human food security in coastal regions. As demand for aquafeed grows, pressure on these wild stocks intensifies, and prices rise accordingly. Ingredients like Azolla, which can be grown locally with minimal inputs, offer a way to decouple part of the aquaculture industry from that extractive supply chain. The Zimbabwe study adds weight to this argument by grounding it in empirical growth data and explicit cost accounting rather than theoretical substitution models, and by situating the analysis at the scale where most African aquaculture actually happens: small ponds, modest budgets and farmers who need every dollar of feed to count.

The authors are careful about the boundaries of their findings. Azolla’s practical value, they note, is greatest where the plant is locally available and where feed costs are a major constraint on aquaculture sustainability, conditions that hold across much of sub-Saharan Africa and tropical Asia. Where Azolla must be transported or cultivated at scale with fertiliser inputs, the cost advantage narrows. The study also implies a need for further work on optimising inclusion levels, processing methods and diet formulation to close the growth gap between Azolla-supplemented and fully commercial feeds, since even partial replacement currently trades some growth performance for cost savings.

Still, the central message is one of achievable, incremental progress. A floating fern that any farmer can grow on a pond surface, incorporated at 15 to 20 percent into tilapia diets, can shave hundreds of dollars off a production cycle while keeping fish growth within acceptable limits and easing demand on wild forage fisheries. In a world where aquaculture must roughly double its output to meet projected protein demand, solutions that are cheap, local and ecologically lighter are exactly what the sector needs. The Chinhoyi team’s work suggests that the future of sustainable fish farming may partly depend on one of the smallest plants in the water.

Subject of Research: Partial replacement of fishmeal with the aquatic fern Azolla pinnata in Nile tilapia aquaculture feeds

Article Title: Evaluating Azolla pinnata as a sustainable and cost-effective partial replacement for fishmeal in Nile tilapia diets

Article References: Daka, B., Mwedzi, T., Utete, B., Mataranyika, P., & Bere, T. (2026). Evaluating Azolla pinnata as a sustainable and cost-effective partial replacement for fishmeal in Nile tilapia diets. Discover Sustainability. https://doi.org/10.1007/s43621-026-04924-w

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04924-w

Keywords: aquaculture, Nile tilapia, Azolla pinnata, fishmeal replacement, feed conversion ratio, alternative protein, sustainable feed, Zimbabwe, small-scale farming, food security, pond aquaculture, feed costs