NOVELTY - Producing biomass, which at least partially comprises aquatic plants for the production of feeds for animal or livestock nutrition, comprises producing plants in a closed photobioreactor provided with stacked culture surfaces, dividing the aquatic culture surfaces of the photobioreactor into zones within the photobioreactor, in which different plant strains and/or plant genera exhibiting different constituent compositions are grown and harvested cyclically. The zones are divided with respect to the attainable harvests which are similar to ratio of constituent composition of the plants.    USE - The method is useful for producing biomass, which at least partially comprises aquatic plants for the production of feeds for animal or livestock nutrition (claimed).    ADVANTAGE - The method: can be carried out in optimized time period; and produces animal feed which reduces the gas formation in the animal intestine and has simple administration in animal husbandry.    DETAILED DESCRIPTION - Producing biomass, which at least partially comprises aquatic plants for the production of feeds for animal or livestock nutrition, comprises producing plants in a closed photobioreactor provided with stacked culture surfaces, dividing the aquatic culture surfaces of the photobioreactor into zones within the photobioreactor, in which different plant strains and/or plant genera exhibiting different constituent compositions are grown and harvested cyclically. The zones are divided with respect to the attainable harvests which are similar to ratio of constituent composition of the plants cultivated in it with respect to the targeted constituent composition of the feed to be produced from a mixture of the harvested plants. INDEPENDENT CLAIMS are also included for:    (1) a device for producing the biomass; and    (2) a feed, mixed feed medium, feed mixtue, or animal bedding for stable (for horse) in animal husbandry, comprising at least one component containing duckweed.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic representation of providing the harvested crop varieties for the production of a compound feed (Drawing includes non-English language text).    Stacking systems (2)    Culture wells (3)    First skimmer (20)    Second skimmer (21)    Feed mixer (30)