Implementation of eco-intensification of common carp ( Cyprinus carpio) aquaculture by improved nutrient management has the potential to diversify production strategies that are much needed in carp farming. Sequestration of nutrients, as well as other compounds, by aquatic plants is a common method to improve water quality. However, common carp aquaculture seeks for low-cost and adaptable solutions to co-produce plants that might be further sold a as a food or feed-grade products to increase overall profitability of the farm. One of the most promising aquatic plants is watercress (Nasturtium officinale), a semi-aquatic perennial plant known for its nutrient-rich leaves and crisp, peppery flavour. Another widespread aquatic plant is duckweed (Lemna sp.), a small floating aquatic plant that may holds immense promise in pond ecosystems. Duckweed offers several benefits when used in carp ponds. For example, duckweed can efficiently remove nutrients such as nitrogen and phosphorus from the water, contributing to improved water quality. The aim of the present study was to assess the production yield of watercress in recirculated aquaculture system (RAS), earthen ponds, and artificial channels, as well as duckweed in pond connecting channels. Additionally, the work evaluated the chemical composition of the plants produced in different systems and analysed possible further directions to use the biomass as food or feed.
The research findings revealed significant variations in water parameters among the experimental points where duckweed and watercress were cultivated. The RAS water showed distinct characteristics compared to other experimental sites, including the lowest pH, dissolved oxygen (DO), and total hardness, along with higher oxidoreductive potential (ORP) and the highest conductivity, alkalinity, and total dissolved solids. Water discharged from the pond with growing watercress had higher levels of DO (approximately 37-38%), temperature (around 3% higher), and reduced phosphorus content (decreased by approximately 33%, compared to inflow). Conversely, in the water at the end of the artificial channel with watercress, there were observed higher levels of pH (approximately 1%), ORP (by roughly 34%), and DO (approximately 5%). Analysis of water from the duckweed channel showed significant variability in parameters such as pH, ORP, DO, temperature, nitrogen, phosphorus, potassium, and inorganic carbon, showing great bioremediation potential.
Furthermore, the results underlined the viability and scalability of watercress and duckweed production within a common carp farm environment. Additionally, the chemical composition analysis revealed that both watercress and duckweed contained high levels of macro and micronutrients (excluding heavy metals), suggesting their potential for utilization in agriculture or related sectors.
Funding
This work was supported by the funding from the European Union’s Horizon Europe programme under grant agreement no. 101084549.