Population growth and utilization of clonal marbled crayfish
A combination of field work, whole-genome sequencing and mathematical modeling recently provided the first size estimate and growth model for a marbled crayfish colony. The results illustrate the capacity of the animals to quickly form large colonies and raise new questions about their utilization.
Marbled crayfish (Procambarus virginalis) are a parthenogenetic freshwater crayfish species that first appeared about 25 years ago. They are closely related to the sexually reproducing slough crayfish from Florida (Procambarus fallax) and have formed a large, genetically homogeneous clone that has been globally distributed through the aquarium trade and through anthropogenic releases. As a consequence, the animals have formed numerous stable wild populations. Our new study describes 15 stable wild populations in 9 European countries and provides evidence for incipient genetic separation of geographically separated populations.
A good example for a stable wild population is provided by the type locality, Lake Reilingen, a small (9 ha) lake close to Heidelberg, Germany. Lake Reilingen is located in a natural preserve and is used for recreational fishing. The animals had been spotted on the shore of the lake for several years, but the size of the population had remained a mystery. To establish a first size estimate for a marbled crayfish population, we used the mark-recapture approach. 18 baited traps were deployed for 10 consecutive days. Every 24 hours, the trapped animals were retrieved and marked with a trap-specific shade of nail polish. The marked crayfish were then released back into the water, at the position where they were initially captured. Over time, many of the marked animals were recaptured and the number of these animals allowed an estimate of the population size. The results suggested that the population consisted of 23,000 adult marbled crayfish, which represents a strikingly high number considering the small size of the habitat and the relatively adverse environment.
Growth models were established based on the population size estimation and the genetic variability found in the population. The results suggested that a population like in Lake Reilingen can form within 4 years. This raises important questions with respect to environmental impacts and potential utilization. In a previous study, it had been shown that marbled crayfish are farmed, sold and consumed in large numbers in Madagascar. Moreover, crayfish (Procambarus clarkii) is currently the most ordered dish in China, with an annual market value exceeding 10 billion USD. This raised the question if the marbled crayfish could also be suited for European cuisine. We gave it a try and asked a chef to prepare a marbled crayfish menu. We started with crayfish tails on avocado mousse, followed by dumplings filled with crayfish meat. This was topped by the main dish of marbled crayfish tails with herbs fried in butter, served on risotto with grilled tomatoes. It was a delicious meal and it served as a starting point for our (still ongoing) analysis of marbled crayfish as a source of nutritional protein.
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