Does Lemna minor Have an Effect on Water Treatment?

In Algeria, aquaculture is an activity in full development to provide the fishing sector with fish production. This policy aims to improve the rate of fish consumption in Algeria, which is unfortunately below the threshold compared to the levels recommended by the World Health Organization. The effectiveness of a feed is reflected not only in the fish’s rapid growth performance, product quality and conversion rates, but also in its impact on the water quality. Duckweed (Lemna minor) is an aquatic freshwater plant, which grows rapidly on the surface of the water. This plant is used as animal feed, as a biofertilizer, for weed and mosquito control and the bioaccumulation of contaminants in water purification. For this purpose, the present study aimed to assess the impact of local foods on water quality, and to study the effectiveness of using Duckweed (L. minor) in tilapia (Oreochromis niloticus) farming as a biological treatment against organic water pollution. Four aquariums were used, each containing 15 individuals of Nile tilapia (O. niloticus), fed with different types of feed (A1: 60%, A2: 35%, A3: 20% and A4: 6% of fishmeal). To better assess the effect of duckweed on reducing nutrient levels in the water, the fry was fed without changing the water in the aquariums ensuring a high nutrient load in the water. Then, the surface of the aquarium was covered with a layer of Lemna. Water samples were taken twice a day for the determination of nutrients (nitrates, nitrites and ammonia), using spectrophotometer colorimetric methods. The results reveal high mortality rates in aquariums fed with feeds containing high percentages of fishmeal (A1 and A2), on day 4 of the experiment. No mortality was recorded after duckweed treatment, with a decrease in nutrient salt concentrations and an increase in water transparency in the different aquariums. The results obtained with duckweed are encouraging and satisfying. Thus, the aquaponic system is recommended for the growth of duckweed and the breeding of fish, simultaneously.