UTILIZATION OF BIOFUEL BYPRODUCTS: HEVEA SEED MEAL  AND SAFFLOWER SEED CAKE AS ALTERNATIVE FEED INGREDIENTS FOR NILE TILAPIA Oreochromis niloticus

Introduction

Between 2022-2024, 91% of total fish production in Sub-Saharan Africa originated from capture fisheries (Davids, 2026). The growth of aquaculture is projected to be 4.8% per annum, projected to the decline of capture fisheries to 87% by 2034. Therefore, there is still a significant potential in further development of aquaculture sector in the region.

Nile tilapia (Oreochromis niloticus) is a freshwater, fast-growing fish native to Africa. However, the demand for tilapia in African markets still mainly relies on imports. China leads in global tilapia production with a total export of 130,300 tonnes frozen whole tilapia within the first 9 months of 2025 (FAO, 2026). Côte d'Ivoire is the largest importer, while exports to Burkina Faso and Mali have also increased. In 2019, a smallholder tilapia farm in Mozambique received EUR 1.4 million investment from IDH Farmfit Fund (FAO et al., 2026), supporting the efforts to expand tilapia production in Africa.

Nevertheless, the aquaculture production in Africa still faces challenges in the production cost. Recent geopolitical tensions and energy market volatility have increased feed production costs affecting global supply chains. Therefore, there is a need to reduce the reliance on imported product by maximizing the utilization of locally-available ingredients. This can also lead to the reduction of aquaculture feed cost. Hevea trees (Hevea brasiliensis, from which natural rubber is obtained) and safflower (Carthamus tinctorius) are commonly cultivated in Africa, with Côte d'Ivoire ranking among top 5 largest natural rubber producer globally. Hevea and safflower seeds have been utilized for biofuel extraction in Africa. The by-product from hevea seeds processing (i.e. hevea seeds meal) contain 23.4±1.1 g/100g protein, 2.88±0.19 g/100g lipid, and 60.63±1.2 g/100g carbohydrate. Meanwhile, by-product from safflower seeds processing (i.e. safflower seeds cake) contain 19.29±0.93 g/100g protein, 19.1±1.2 g/100g lipid, and 52.76±1.54 g/100g carbohydrate. Despite their potential nutritional value, these by-products remain underutilized. Therefore, this study investigates the utilization of these byproducts extracted from hevea and safflower seeds, commonly utilized for biofuel production, as alternative feed ingredients for juvenile Nile tilapia.

Materials and Methods

Rearing conditions

Nile tilapia larvae were obtained from Wageningen University, Netherlands, and reared at the Laboratory of Aquaculture, Department of Veterinary Medical Sciences, University of Bologna (Cesenatico, Italy). Larvae were fed commercial diet (Skretting, Perla Plus 2.0). When reached 20 ± 5 g (juvenile stage), 50 tilapia were randomly distributed to 21 tank connected to recirculated aquaculture system (RAS) (three replicates per dietary treatment) equipped with mechanical sand filtration, ultraviolet lights, and a biofiltration as described by Parma et al. (2023) and reared for 1.5 month. Water parameters were maintained at 24 ± 1.0 °C, 0.5 ± 0.5 g/L salinity and oxygen levels at 8.0 ± 1.0 mg/L using a liquid oxygen system.

Diet

To simulate the potential conditions of an aquafarm in remote areas of the African countries, where limited technological advancement is in place and cost of shipping of materials as well as the pelleted feed from accredited feed companies is prohibitive, diet was produced within the laboratory using an automatic pasta-making machine (La Monferrina P12). The resulting spaghetti-shaped pellet were blended and sieved to generate pellet of 1 to 2 mm. After production, pellets were dried in an oven.

Fish were fed twice daily using an automatic feeder six days per week, with 7 different isoproteic, isolipidic, and isoenergetic diets:

Diet 1: control diet

Diet 2: 10% inclusion of hevea seed meal

Diet 3: 20% inclusion of hevea seed meal

Diet 4: 30% inclusion of hevea seed meal

Diet 5: 10% inclusion of safflower seed cake

Diet 6: 20% inclusion of safflower seed cake

Diet 7: 30% inclusion of safflower seed cake

Figure 1. Grinded hevea seeds meal (left) and safflower seeds meal (right).

Sampling

At the beginning and end of the experiment, all fish are anesthetized or euthanized with tricaine methanesulfonate (MS-222). Growth performance and whole-body and dietary proximate analyses parameters are calculated. Additionally, gut microbiota and plasma biochemistry were also sampled and analyzed. Moreover, digestibility of hevea seed meal and safflower seed cake was analyzed with yttrium oxide in a 2-week period after the end of the feeding trial. All experimental procedures were approved by the Ethical Scientific Committee for Animal Experimentation of the University of Bologna (ID 113/2020-PR), following European Directive 2010/63/EU.

Results and Discussions

Preliminary results suggest that the inclusion of hevea seed meal and safflower seed cake at 10 and 20% could do not significantly affect the growth performance of juvenile tilapia. The protein content of both hevea seed meal and safflower seed cake can adequately meet the dietary protein requirements, and the lipid content of safflower seeds meal can fulfil the dietary lipid needs. Negative impact on the growth performance was observed at 30%, which can be caused by the relatively high crude fibre content in the diets (Suprayudi et al., 2016).

Nevertheless, at 10 and 20% inclusion, hevea seed meal or safflower seed cake can lead to the replacement of 15-30% of soybean meal and 20-40% of wheat flour. Despite this, digestibility of these alternative ingredients is lower than that of conventional feed components. Notably, a diet containing 10% hevea seed meal and 10% safflower seed cake exhibits digestibility comparable to the control diet, whereas higher inclusion levels result in reduced overall diet digestibility. This decline in digestibility likely limits nutrient availability and absorption, thereby contributing to observed differences in growth performance.

The reduced digestibility and acceptance may be attributed to the presence of anti-nutritional factors, such as tannins and phytic acid, in both hevea seeds meal and safflower seeds cake. Additionally, processing methods, including dehulling and heat treatment, may further influence nutrient availability and palatability, thereby affecting feed utilization efficiency.

Conclusions

The preliminary findings support the utilization of hevea and safflower seeds from biofuel by-products as feed ingredients for Nile tilapia, reducing the dependence on imported soybean meal in Africa.

References

Davids, P. (2026). Sub-Saharan Africa: Medium-term projections 2025–2034. Rome, FAO.

FAO. (2026). GLOBEFISH Quarterly Tilapia Analysis – February 2026. Rome, FAO.

FAO, ECA, WFP and AU. 2026. Africa Regional Overview of Food Security and Nutrition 2025 – Financing towards agrifood systems transformation for food security and improved nutrition. Accra.

Parma, L., Busti, S., Ciulli, S., Volpe, E., Errani, F., Oterhals, Å., Romarheim, O.H., et al. 2023. «Growth, plasma biochemistry and immune-related gene expression of European sea bass (Dicentrarchus labrax) fed bioactive peptides from farmed salmon by-products». Aquaculture 563:738982. https://doi.org/10.1016/j.aquaculture.2022.738982.

Suprayudi, M. A., Alim, S., Fauzi, I. A., Ekasari, J., Setiawati, M., Junior, M. Z., & Tacon, A. G. (2017). Evaluation of hydrolysed rubber seed meal as a dietary protein source for Nile tilapia Oreochromis niloticus L. Aquaculture Research, 48(7), 3801-3808.