The introduction of non-native species is recognized as a major threat to biodiversity, particularly in freshwater ecosystems. Pikeperch Sander lucioperca, is a recent invader to Portugal, primarily providing commercial and angling interest. The aim of this work was to study the diet of this top predator across Portuguese basins and to evaluate its potential impact on recipient ecosystems. In total, 256 pikeperch stomachs from seven basins were examined, of which 88 (n = 34%) were empty. Pikeperch diet was dominated by R. rutilus, M. salmoides and Diptera in northern populations, while A. alburnus, P. clarkii and Atyidae were important prey in more humid highlands. Variation in diet was most strongly linked to latitude and ontogeny, with both size classes showing signs of cannibalism. The population niche breadth remained low and was accompanied by higher individual diet specialization, particularly in northern populations. Pikeperch dietary patterns denoted an opportunistic ability to use locally abundant prey in each ecosystem, and was size dependent, with larger individuals becoming more piscivores, causing a higher impact in the lotic systems. This first perspective about the pikeperch diet presents a very broad view of the feeding traits of this non-native predator across Portugal, being very important to deepen our knowledge about the impact of these introduced piscivores.

The sand gobies are a group of 30 species in five genera (Knipowitschia, Pomatoschistus, Economidichthys, Ninnigobius and Orsinigobius) native to the seas and fresh waters of Europe and the Ponto-Caspian region. We construct a phylogeny incorporating new DNA sequence data (mitochondrial COI gene) for species in Greece and the Adriatic (Venetian Lagoon) with existing sequences sampled from throughout European waters. Our comprehensive analysis confirms the distinctness of Orsinigobius and Ninnigobius, supports that Gobiusculus is part of Pomatoschistus and supports the monophyly of Economidichthys and Knipowitschia. We then calibrate the phylogeny using fossils, interpret the phylogenetic biogeography of sand gobies throughout Europe and the Mediterranean and estimate the historical divergence patterns in the group. We infer the origin of the sand goby clade at 33.0 Mya, near the Eocene–Oligocene boundary, and show that radiations among marine Pomatoschistus clades in the Miocene are correlated with the closure of the Tethys seaway. Younger freshwater clades of Ninnigobius, Orsinigobius and subclades of Knipowitschia diversified in the late Miocene and early Pliocene, centred in the Adriatic region and concordant with the Lago Mare phase of the Messinian salinity crisis. Economidichthys is the exception to this pattern; it inhabits freshwater but originated and diversified during the mid-Miocene.

The genetic structure of Aphanius fasciatus populations has been analysed using two mitochondrial DNA (mtDNA) markers (16S rRNA and D-loop) obtained from specimens collected in nine sites from the Venice lagoon, Comacchio saltworks and Corsica. Available GenBank sequences were also included, in order to extend the results on a Mediterranean scale. Genetic polymorphism within the Venice lagoon was very low, with most of the specimens analysed (66% for 16S rRNA and 83% for D-loop) sharing the same haplotype for either of the two markers. The genetic homogeneity found within the Venice lagoon may be the consequence of the northward migration of southern Adriatic populations after the Last Glacial Maximum: mismatch analysis showed indeed clear signs of a rapid demographic and spatial expansion. To explain this genetic homogeneity other hypotheses were also suggested, such as adaptation to the high variability of brackish water habitats, and artificial introductions. On a Mediterranean scale, phylogenetic analyses showed the presence of five distinct geographical lineages: Aegean Sea, Greek coast of the Ionian Sea, Adriatic Sea, Tyrrhenian Sea and Southern Sicily. Analysis of molecular variance revealed a genetic partitioning mainly due to differences between groups presumably due to late Miocene geological events, while less polymorphism was present within groups and populations.

Hybridization between native and nonnative fish species is a major conservation issue, especially in ecosystems with high levels of endemism, such as Iberian streams. To date, hybridization with the invasive bleak Alburnus alburnus has been reported for the Iberian chub Squalius alburnoides and S. pyrenaicus and in scattered locations only. However, the bleak is spreading in the region, potentially increasing the risks of hybridization with other Squalius species. To gather a more comprehensive picture on the current geography of hybridization, we compiled records on hybrids between bleak and chub in Portugal and conducted genetical assessments of hybrids between bleak and S. carolitertii. We found that hybridization with bleak is widespread throughout Portuguese river basins and involves at least S. alburnoides, S. pyrenaicus and S. carolitertii. Hybridization with bleak may not only cause waste of reproductive effort and damage the genetic integrity of these endemic species but also promote shifts in the reproductive dynamics of the S. alburnoides hybrid complex, which includes individuals with various ploidy levels and combinations of parental genomes, reproducing sexually and asexually. We recommend that future studies characterize the fitness of bleak hybrids and their ecological and genetic interactions with native fish, in order to design effective conservation measures.