The body condition of invasive crayfish Faxonius limosus (Raf., 1817) (Decapoda: Cambaridae) is better in small rivers than in dam reservoirs in Central Europe.

The impact of dam reservoirs on river ecosystems is one of the current major issues in hydrobiology. In addition to the impact on native biodiversity, impoundments may facilitate biological invasions. A successful invasion is presumably related to the individual life history and resource allocation strategy in expanding populations. We tested whether reservoirs affect the body condition of invasive Faxonius limosus in upland streams. We found positive allometry of growth in females but more frequent isometric growth in males, and the form factor a was significantly higher in males than in females within populations. Fulton's condition factor (K) was calculated for standard carapace lengths of 20 mm (juvenile) and 40 mm (adult). Both mean K and K were higher in males than in females. Positive allometry of growth in females resulted in a larger mean K than K. The majority of the mean K obtained in reservoirs was similar or lower than the respective condition in streams. The condition of adult females was higher in streams in comparison to reservoirs. The obtained results are in contrast to the hypothesis that reservoirs positively affect individual body conditions and show that these man-made lakes do not provide more favourable habitat conditions for F. limosus than those in the natural aquatic environments of an upland landscape. An advantageous effect of the presence of reservoirs on invasion spread may be possible in more ecologically harsh landscapes, especially in colder climatic zones. Our study is the first to investigate the relationship of the body condition of F. limosus in two contrasting habitats.