Sustainable rearing of crayfish in a recirculating aquaculture system using the example of Astacus astacus

Abstract

The aim of this study was to examine the potential of a recirculating aquaculture systems for a sustainable culture and reproduction of a European crayfish species. Since the endangered Noble crayfish Astacus astacus formerly was a common food source in Europe it presents the economically most interesting native species and was selected for this study. The collaboration with an open pond farm was established to collect and deliver scientific comparative data about crayfish performance under almost natural conditions. Abiotic and biotic parameters like water conditions, growth, density and shelter requirements were recorded. The experiments aimed at establish comparative conditions in a recirculating aquaculture system in accordance with the restrictions of such an artificial system. Results showed that Noble crayfish can be cultured and reproduced in a recirculating aquaculture system. The reproduction under artificial conditions delivered best results using a five minutes salt bath (26.6% RAS, P = 0.015) and excellent hatch rates especially in comparison to open pond systems (100% RAS vs. 20% OPS). Crayfish demands can be answered with e.g. adequate feeds and shelter constructions even though these are not available on the market and have to be manufactured. In addition, stocking densities were increased to promising numbers (RAS 10 Krebse/mAA , OPS 1-2 Krebse/mAA ). Therefore, an economic culture of Noble crayfish in a recirculating aquaculture facility is possible in the long-term but primarily given the moderate growth performance of adult crayfish (RAS 0.78/1.33% SGR) and high investment costs not worthwhile for investors since more profitable and fast-growing species can be produced for the growing market. A polyculture of Noble crayfish and Red Nile tilapia showed the advantage of a co-culture as cleaning intervals are reduced due to finfish bioturbation and feed conversion is increased without a negative impact on growth (ANOVA, p 0.05). It can be summarized that recirculating aquaculture systems can successfully be used for reproduction and culture of Noble crayfish since they deliver high controllable and secure conditions, of especially for juvenile crayfish. The species requirements can be met even though there is space for improvements in e.g. feed composition and shelter design in regard to technical and economic limitations of recirculating aquaculture systems. The high investment and maintenance costs do not bear good prospects for a mono-culture even for the high value Noble crayfish but a polyculture is within the bounds of economic possibility and offers several advantages. For crayfish conservation actions and further scientific research recirculating aquaculture systems offer excellent conditions especially in the face of the threatening crayfish plague. Taking into account economic aspects of a crayfish culture based on this cost-intensive technique a combination of recirculating aquaculture systems together with more unsecure but convenient open pond systems seems the best compromise about safety and economic arguments to produce native crayfish for restocking purposes. The combination with an open pond system opens the opportunity to not even produce summerlings but adult crayfish at reasonable prices which are necessary for complete restocking actions.