| The LeTe-Protein project aimed at evaluating both the potential and challenges of obtaining protein sources from duckweed (Lemna minor) and mealworm larvae (Tenebrio molitor) used as raw materials for animal feed production.
Two main objectives were pursued for the utilisation of remaining materials. On one hand, residual material from herb processing was used as substrates for rearing mealworm larvae. On the other hand, nutrient-rich fish wastewater from the recirculation system was used to produce duckweed.
The duckweed production was carried out in two stages. It was firstly started with the cultivation of duckweed in a test facility of approximately 8 m² and subsequently scaled up to 100 m². Overall, the plants showed very high protein contents between 33 and 42.5% crude protein in the dry matter. The harvest quantities of duckweed increased almost continuously until the end of the project. However, it also became apparent that duckweed tends to accumulate elements. In addition to high levels of sulfur, zinc, or manganese, the samples also showed very high levels of arsenic, lead, or cadmium, which in some cases exceeded the permissible maximum levels of Directive 2002/32/EC.
The production of mealworm larvae also showed significant growth since the beginning of the project. The size of the population, the housing conditions, and many work steps were optimized during the project. To determine the optimal substrate, mealworm larvae were fed with various residues from herb production. The results showed that green meal pellets from rye are an alternative to the standard substrate. For larvae fed with flaxseed by-products, the proportion of omega‑3 fatty acids increased from 1 – 2 g/100 g fat to 15 – 32 g/100 g total fatty acids.
In a feeding trial with brook trout (Salvelinus fontinalis), the acceptance of the experimental feed was tested compared to conventional fish feed. However, the fish receiving the experimental feed showed a yellow-green coloration, especially on the belly and fins, compared to the control group, which is presumably due to the high carotenoid content of duckweed. These needs to be further evaluated.
The LeTe-Protein project thus laid the foundation for circular fish feed production, but it also shows obstacles that still need to be investigated in order to use regional, high-quality protein sources as fish feed. |