Recently, the ZEEVIVO-project (Dutch acronym for Sea Fish Feed) has been successfully completed after 4 years. Van Hall Larenstein University of Applied Sciences, NIOZ, Wageningen University & Research, Danvos and Hortimare examined if seaweed could offer a suitable and sustainable alternative for fish feed. It appears that Tilapia, a popular fish in nurseries used for consumption, that has been fed with seaweed-based feed, grows equally as fast as Tilapia fed with commonly used fish feed. Provided that the protein content of the seaweed has been increased.
The fish feed industry is looking for alternative protein sources for the widely used fish meal or soy. Seaweed has the potential to be a sustainable alternative, provided that the protein content of the seaweed is equal or higher than the product it replaces. Soy contains 40% of protein, and fish meal no less than 60%. Depending on the species and the season, seaweed has a protein content between 10 and 20%.
Increasing the protein content of seaweed
Research during ZEEVIVO showed, that adding nitrate results in higher growing rates and higher protein content in seaweed. The increase of the protein content occurred so quickly, that it is possible to enrich seaweed by growing it under elevated nitrate content for 2 weeks prior to harvest. In addition, the protein from the seaweed has been further concentrated through bio refinery. In this process, the seaweed has been brought into a solution with increased pH and temperature causing a part of the protein to dissolve. This liquid has been further concentrated through membrane filtration, resulting in seaweed products with over 30% of protein.
Opportunities to make aquaculture more sustainable
In the ZEEVIVO-project, three different seaweed products, based on the green seaweed Ulva lactuca, the red seaweed Solieria chordalis and a 50:50 mix of both, were used to replace soy in the Tilapia feed. During two feeding tests, the growth rates of the Tilapia that were fed with the experimental seaweed feed were compared with the outcomes of a standard reference diet.
The first test, in which 25% of the soy protein was replaced by the seaweed protein, showed that the feed intake and growth of the fish was similar for all feeds used. The second test, replacing 20% of the reference diet by the different seaweed products, showed similar results on growth and feed conversion in comparison to the fish fed with the standard reference diet and to the fish fed with a diet based on the seaweed product from the green seaweed Ulva lactuca. The ZEEVIVO-project shows that seaweed products containing sufficient protein could be suitable to replace or at least partially replace the soy component in Tilapia feed. These findings could have a global impact on the production of cultivated fish and enhancing the sustainability of the aquaculture sector.
In the ZEEVIVO project the University of applied sciences VHL, NIOZ, WLR, WMR, Danvos and Hortimare collaborated on a seaweed product with a maximum protein content. The project was co-financed by the Dutch Taskforce of Applied Research (Dutch: Regie Orgaan SIA), part of the Dutch Research Council (NWO).