Patterns, latitudinal clines and countergradient variation in the growth of roach Rutilus rutilus (Cyprinidae) in its Eurasian area of distribution

Abstract

The roach Rutilus rutilus is a eurythermal generalist that has been translocated and introduced mainly beyond the southern limits of its native Eurasian range of distribution. Although largely studied in most aspects of its ecology, no global assessment is available on its growth. Such information is critical for management purposes, especially in view of further dispersal of this 'potential pest' and climate change predictions. To address this knowledge gap, a meta-analysis was carried out of the age and growth of 301 roach populations from 231 water bodies across the species' native and translocated/introduced Eurasian range of distribution with the aim to identify habitat and climate-related differences in growth patterns, latitudinal clines, and the possible presence of countergradient growth variation (CGV). Faster growth rates were identified under warm relative to temperate and cold climates, and these were related to optimised resource allocation. Latitudinal clines indicated decreasing trends with increasing latitude in growth and body size, in line with life-history theory. However, the presence of thresholds encompassing the previously-reported 50A degrees N latitude value suggested a 'plateau' or decrease in growth at lower latitudes, and CGV was identified for 1+ to 10+ fish. It is argued that increased water temperatures are likely to cause a northern shift in the observed thresholds and a 'homogenisation' of the species' population dynamics resulting in faster growth rates, but with more pronounced effects in continental Eurasia.