North American black bullhead, Ameiurus melas, which were introduced to Europe in the nineteenth and twentieth centuries, have received relatively little study. With focus on growth and reproduction, this extensive review, which includes new European data, aims to inform the risk analysis process concerning this non-native species in Europe. Surprisingly, the new data for Europe were more comprehensive than for native populations, with data available mainly from Oklahoma, and North and South Dakota (USA). In terms of relative growth, juvenile A. melas were found to have a relatively uniform body shape regardless of the population's origin, whereas adults developed different phenotypes depending upon location. Overall growth trajectory was significantly faster for native than for non-native populations.Growth index values decreased significantly with increasing latitude in non-native but not native populations-the latter decreasing weakly with increasing altitude in the populations located at latitudes \40°. Mean general condition (slope 'b'), mean sex ratio and mean egg diameter did not differ significantly between native and non-native populations. Absolute fecundity was slightly (but not significantly) higher in non-native than native populations. GSI data, which were very scarce for native populations, suggest gonad production may be slightly higher in native than in non-native populations. Precise data on age at maturity (AaM) are lacking for the native range, where 2-5 years is reported. Whereas, in the introduced range the greatest AaM was 3.5 years, and AaM decreases with increasing juvenile growth (TL at age 3). The populations with fastest juvenile growth tended to be from warmer water bodies where they are considered to be invasive. The great growth and life-history plasticity of black bullhead affords the species great potential to invade and establish viable populations in new areas.
Stomach contents of 331 specimens of Perccottus glenii (Perciformes: Odontobutidae) were analysed. Chironomids and ephemeropterans dominated the diet of all size classes of fish; however, the frequency of crustaceans was also high. Micro-crustaceans (ostracods, copepods and cladocerans) dominated in lower size classes (20-39 mm); macro-crustaceans (Isopoda, Amphipoda) dominated in higher size classes (up to 79 mm). The proportion of crustaceans decreased from the size class 80-89 mm. With the increasing size of fish the frequency of molluscs (Gastropoda) increased, the maximum was in size class 70-79 mm. Cannibalism occurred from 60 mm, and it was significant from 80 mm. The highly mobile invertebrates (Coleoptera, Heteroptera) were found in the largest size classes. In middle size classes (40-59 mm), the widest spectrum of prey units was documented; the food variability of small (<40 mm) and large (>90 mm) individuals was poor. Differences in the diet composition of small individuals were negligible; the diet of the largest ones differed significantly. According to diet, two feeding size class groups were recognised: the first <70 mm and the second ≥70 mm. Main differences between these groups were caused by feeding on molluscs, important was also the occurrence of cannibalism. Positive prey selection was shown for slowly moving invertebrates from the bottom or vegetation and negative prey selection for highly mobile invertebrates.
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