To evaluate the potential invasiveness of pumpkinseed Lepomis gibbosus introduced to northwestern European inland waters, growth and reproduction traits were examined in ten populations along a trajectory spanning northwestern Europe (Norway, England, Holland, Belgium and France) and evaluated in light of published dataset from Europe. In the 848 pumpkinseed captured, maximum age was 3-4 years, with a sex ratio near unity in all but one population. Significant variations with increasing latitude were observed in adult growth (age 2-3 increment in total length, TL) and mean age at maturity (A M ), with

To assess the spatial variability in external morphology of non-native populations of topmouth gudgeon Pseudorasbora parva within an ontogenetic context, triple regression analysis (distance-based measurements) was applied to data from eight European populations (two Slovak, four Romanian, one English and one French). The data from Slovakia were also subjected to geometrical analysis (co-ordinates-based measurements) to obtain a more complex picture of the species' overall morphology. Great phenotypic variability was observed, being expressed not only in the formation of different definite phenotypes but also in the manner by which the phenotypes are achieved. Thus, both the definite phenotype and the patterns of development in invasive P. parva may be highly influenced by environmental conditions. Such great morphological (phenotypic) variability is likely to be one of the attributes that make this species such a successful invader.

Females of an invasive population of topmouth gudgeon Pseudorasbora parva (Temmick and Schlegel, 1846) from the Sˇu´r pond (Bratislava, Slovakia) were examined to analyze their fecundity and other life history traits. Samples were collected during both pre-spawning (n = 137) and postspawning (n = 89) periods. Standard length of the females from the pre-spawning period ranged from 23.42 to 59.71 mm (mean 32.80 mm), body weight from 0.260 to 5.442 g (mean 0.965 g), and eviscerated body weight from 0.207 to 4.882 g (mean 0.748 g). Absolute fecundity varied between 121 and 7124 oocytes (mean 1106 oocytes). In 75.22% of the females, two or three size groups of oocytes were clearly distinguished. Overall, the life history traits observed in invasive topmouth gudgeon from the Sˇu´r pond demonstrated a high flexibility in their reproductive strategy. This, together with previously described great morphological variability, is likely to make this species such a successful invader.