Tönges S, Masagounder K, Gutekunst J, Lohbeck J, Miller AK, Böhl F, Lyko F. 2020. Physiological properties and tailored feeds to support aquaculture of marbled crayfish in closed systems. bioRxiv: 2020.2002.2025.964114. https://doi.org/10.1101/2020.02.25.964114 (Unreviewed preprint)Abstract
The marbled crayfish (Procambarus virginalis) is a new freshwater crayfish species, which reproduces by apomictic parthenogenesis, resulting in a monoclonal, all-female population. The animals have become a popular source for nutritional protein in Madagacar and are increasingly being considered for commercial aquaculture. However, their potential has remained unclear and there are also significant ecological concerns about their anthropogenic distribution. We show here that the size and weight of marbled crayfish is comparable to commonly farmed freshwater crayfish. Furthermore, purification of chitin from marbled crayfish shells revealed a high chitin content, which can be utilized for the synthesis of chitosan and other bioplastics. To allow the further evaluation of the animals in closed aquaculture systems, we used a factorial modeling approach and formulated tailored feeds that were matched to the marbled crayfish amino acid profile. These feeds showed superior performance in a feed trial, with a noticeable feed conversion rate of 1.4. In conclusion, our study provides important data for a balanced assessment of marbled crayfish as a new species for sustainable aquaculture and a feed that allows their culture in closed systems.
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1 comment:
The marbled crayfish is not suitable for aquaculture, neither for the production of meat nor chitin and chitosan for the following reasons:
1. Marbled crayfish is too small a species for aquaculture. It is much smaller than the well established Astacus, Pacifastacus and Cherax species and considerably lighter than Procambarus clarkii, the most intensely cultured freshwater crayfish. Figures 1A and B of the paper depict the by far largest marbled crayfish ever collected or raised. Figure 1C shows that of 1537 specimens collected with traps only 11 (0.7%) were heavier than 30 g and 30 (2%) were heavier than 20 g. Specimens <20 g are of litte or no value for the market. In contrast, in a Procambarus clarkii population harvested by Wang et al. (J. Freshwater Ecol. 26, 287-294, 2011) from a pond more than 50% of the 678 specimens had weights >30 g and the heaviest specimen had a weight of 83 g (compared to 49 g in marbled crayfish, figure 1B). All of the marketable marbled crayfish from the different collection sites in Madagascar and Germany together had a total weight of about 1 kg (figure 1C). In Spain, you would get less than 5 US$ for the entire harvest based on the Procambarus clarkii market prices. That´s nothing.
2. The meat of marbled crayfish is rich in valuable proteins as in any other crayfish. Therefore, it is principally a valuable food commodity, particularly in developing countries like Madagascar, where these animals are collected from natural water bodies and rice fields without having any production cost. Hope we agree that this highly invasive species must not be transferred to natural waterbodies of other developing countries because of its high invasiveness and negative effects on the native fauna and ecosytems. The introduction of Procambarus clarkii into many countries around the world for aquaculture and fisheries is an illustrative example for a seemingly good idea that has turned into the opposite (e.g., devastating effects in Spain and Kenia).
3. Freshwater crayfish including the high-priced species are cultured in extensive and semi-intensive (additional feeding of pellets) outdoor facilities, mostly in earthern ponds. Procambarus clarkii is additionally produced in polyculture with rice. This mode of culture is not possible for marbled crayfish, because they can easily escape from such facilities and establish natural populations with all the negative effects. I am not aware of any intensive crayfish indoor culture with closed water circulation with the exception of research facilities which don´t have to be profitable. Occasionally, the vulnerable early life stages of the high-priced species are raised in intensive indoor facilities until stocking of outdoor grow-out ponds. The costs for buildings, artificial feeds and labor would be much too high for an intensive closed indoor system of marbled crayfish to be profitable, even in developing countries with low labor cost.
4. I am not familiar with the market of chitin and chitosan but actually these products are mainly obtained from crustacean waste, the shells. Culture of the marbled crayfish just for the production of these materials is apparently no good idea. Large insects like migratory locusts are probably much cheaper resources for bioplastics than marbled crayfish from intense indoor cultures.
5. EU Regulation No. 1143/2014 prohibits keeping and breeding of marbled crayfish in the European Union, placing on the market and releasing into the environment. Keeping for scientific purposes is allowed. In the United States there are similar regulations in several states. I am quite convinced that in the EU, Northern America and Australia nobody would get a licence for aquaculture of marbled crayfish, not even for closed indoor systems.
Therefore, the marbled crayfish is unsuitable for any type of aquaculture in any country.
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