Duckweed feed - duckweed protein for fish feed
Limaskarehu
The starting point for this project was the idea of Kalankasvatus Vääräniemi Oy to grow small slime (Lemna minor) as a feed raw material. In this project, the nutrient discharges from the fish farm's discharge waters are used for the slime cultivation, which is then returned to the plant in the form of new feed. The cultivation has been tested in the Rehulimaska project, which was co-financed by the Kalaleader of Kainuu and Koillismaa. In this project, small slime was grown using nutrients from the discharge waters of Kalankasvatus Vääräniemi Oy's Oudonjoki facility, from which a protein-rich product intended for fish feed was produced. The method was based on fermentation.
Small slime is a wild small aquatic plant that grows on the surface of the water. It takes its nutrients from the surrounding water and, under suitable conditions, it grows quickly. Its protein content is quite high compared to plants growing on land.
The results obtained in this project are similar to similar experiments in recent years. They also found that adding slime to feed slightly reduces fish growth: Fiordelmondo and colleagues found that adding slime slightly reduced fish growth (https://doi.org/10.3390/plants11091220). A similar feeding experiment and observations have also been made by Stadtlander and colleagues (https://doi.org/10.1016/j.jclepro.2019.04.196).
If slime were to be used as a soy substitute in feed in the future, for example, their carbohydrate content would need to be reduced. In this case, the protein content of slime flour could be increased to the level of corresponding soy products, which typically varies between 60-70% depending on the preparation. At the same time, the concentrations of growth-retarding ANF compounds would also decrease, which would improve the absorption and utilization of the feed in the fish's digestive system. The carbohydrate content has been reduced, for example, by adding yeast cells to the fermentation mixture. As they grow, they convert some of the carbohydrates into alcohol, which evaporates during feed processing.
