Recirculating aquaculture systems (RAS) represent an environmentally friendly approach to fish production by enabling water reuse and thereby significantly reducing overall water consumption. An extension of this concept is the integration of hydroponic plant production, in which plants utilize dissolved nutrients excreted by fish and produced by the biofilter. This further reduces the need for water exchange and enhances overall nutrient recycling within the system.

However, the handling of solid waste fractions, particularly fish faeces, remains a challenge. To address this issue, the University of Klaipėda further advanced the concept within the PILOT 3 framework by integrating crayfish into the production cycle with the aim of consuming and metabolizing suspended solids within the system.

Experimental setups included combinations of rainbow trout and noble crayfish in cold-water systems, Siberian sturgeon and narrow-clawed crayfish in cool-water systems, as well as Nile tilapia and Australian red claw crayfish in warm-water systems. Preliminary results indicate that noble crayfish were able to significantly reduce sludge accumulation in the system. In contrast, narrow-clawed crayfish did not show a measurable effect on sludge reduction.

A common observation across both trials was the lack of growth in crayfish biomass, which is likely attributable to the low caloric and energetic value of the sludge as a feed source. These findings suggest that optimized or mixed feeding strategies may be required to improve feeding efficiency and enable marketable crayfish production. In addition, the composition of fish faeces and the lipid content of the formulated feed may represent important factors influencing overall system performance.