Species composition of introduced and natural minnow populations of the Phoxinus cryptic complex in the westernmost part of the Po River Basin (north Italy)

Seasonal Effects on Health Status and Parasitological Traits of an Invasive Minnow in Iberian Waters

Biological invasions are of special conservation concern in the Iberian Peninsula and other regions with high levels of endemism. Environmental variability, such as the seasonal fluctuations of Mediterranean streams, is a key factor that affects the spread of aquatic species in novel habitats. Fish parasites have a great potential to reflect such changes in the habitat features of freshwater ecosystems. The aim of this study consisted of seasonally analysing the health status and parasitological traits of non-native fish in Iberian waters. In particular, a strongly invasive population of Languedoc minnow Phoxinus septimaniae (leuciscid species native to south-east France) was assessed in Tordera Stream (north-eastern Iberian Peninsula, Mediterranean conditions). Fish were sampled in April, July, and October 2023 by electrofishing. Health status (external/internal organs) was significantly better in autumn (HAI = 28.8) than spring (HAI = 35.6). Life-cycle complexity was higher in spring (LCI = 1.98), whereas parasite abundance and Shannon diversity were significantly lower in autumn (TA = 19.6 and H' = 2.15, respectively). In October (more 'benign' environmental conditions in Iberian streams), minnows could display elevated foraging activity, with fish increasing their health condition and level of parasite resistance/tolerance. Overall results showed a particular seasonal profile of health and parasite infra-communities that allow this minnow species to thrive under highly fluctuating habitat conditions. This information could help environmental managers to control non-native fish in Mediterranean streams.

An integrative approach highlights the discrepancy in the genetic, phenotypic, and presumptive taxonomic structure of Phoxinus (Actinopterygii, Leuciscidae, Phoxininae) in Bulgaria

The present drainage network of Bulgaria is the result of a complex Neogene and Quaternary evolution. Karst, which has developed on 23% of the territory, further complicates the hydrological pattern. Fresh waters of Bulgaria drain into the Black Sea and the Aegean Sea basins and can be roughly divided into the Danube (Middle and Lower Danube), non-Danube Black Sea, East Aegean, and West Aegean hydrological regions. Phoxinus, a small leuciscid fish, has a mosaic distribution in all four of these regions, inhabiting small mountainous and semi-mountainous streams. Based on morphology, it was identified as three species, Phoxinus phoxinus in the Danube, Phoxinus strandjae in the non-Danube, and Phoxinus strymonicus in West Aegean region. Later, molecular data revealed Phoxinus csikii and Phoxinus lumaireul in the Middle Danube and P. csikii in the Lower Danube. Phoxinus has been the focus of many studies, showing a high molecular and morphological diversity, which is not entirely consistent with previous morphology-only-based taxonomic concepts. In this study, molecular (a mitochondrial marker and a nuclear marker) and morphological data from both historical and recently sampled collections were analysed to assess the applicability of the integrative approach in Phoxinus. The results showed a significant influence of the complex paleo- and recent hydrology on the currently observed genetic structure of the considered populations and species. Furthermore, the study also demonstrated a strong influence of phenotypic plasticity on the morphological analysis of Phoxinus and the lack of a clear differentiation between P. csikii and P. strandjae. A barcoded specimen was designated as neotype to fix the species named P. strandjae in the current taxonomic concept. Finally, a significant discordance between genetically delimited clades and phenotypic groups did not allow a proper delineation of the species distributed in Bulgaria, demonstrating that more molecular markers are needed for further taxonomic study of the Phoxinus complex.

Phoxinus abanticus, a new species from the Lake Abant drainage in Türkiye (Teleostei: Leuciscidae)

Phoxinus abanticus, a new species, is described from the Lake Abant basin. It is distinguished from Phoxinus species in Türkiye and adjacent waters by the presence of fewer lateral line scales (60-69, vs. 75-91 in Phoxinus colchicus, 75-90 in Phoxinus strandjae); a deeper caudal peduncle (caudal peduncle depth: 1.8-2.3 times in length, vs. 2.4-2.9 in P. colchicus; 2.5-3.2 in P. strandjae); the absence of scales in the breast of males (vs. present); and ventral body reddish in nuptial colouration pattern for male (vs. brackish). The new species, P. abanticus, is also distinguished from its closest relative, P. strandjae, by a minimum of 3.40% genetic distance in the mtDNA cytochrome b (cyt b) gene.

A new set of microsatellite markers for Phoxinus lumaireul senso lato, Phoxinus marsilii and Phoxinus krkae for population and molecular taxonomic studies

Minnows of the genus Phoxinus are common and an often highly abundant fish species in Palearctic freshwater habitats. Phoxinus species have a complex evolutionary history, phylogenetic relationships are not well understood and there are a number of unresolved taxonomic problems. There are currently 23 different mitochondrial genetic lineages identified in the genus Phoxinus, 13 of which are recognized as valid species. The taxonomic status of these lineages requires resolution, including the degree to which they can interbreed. Suitable nuclear molecular markers for studies of population divergence and interbreeding between morphotypes and mitochondrial lineages are lacking for Phoxinus species. Therefore, the authors developed a set of microsatellite markers using genomic information from Phoxinus lumaireul and tested their suitability for this and two related species, Phoxinus krkae and Phoxinus marsilii. Out of 16 microsatellite candidate loci isolated, 12 were found to be in Hardy-Weinberg equilibrium when tested on two P. lumaireul senso lato populations. Seven loci amplified across the three species, enabling the study of intraspecific genetic diversity and population structure within P. marsilii and P. krkae. The markers were able to clearly resolve differences among the three tested species, including the recently described P. krkae, and are therefore suitable for the detection of introgression and hybridization among populations consisting of mixtures of two or more of P. lumaireul s. l., P. marsilii and P. krkae.

Phylogeography of Sarmarutilus rubilio (Cypriniformes: Leuciscidae): Complex Genetic Structure, Clues to a New Cryptic Species and Further Insights into Roaches Phylogeny

Italy hosts a large number of endemic freshwater fish species due to complex geological events which promoted genetic differentiation and allopatric speciation. Among them, the South European roach Sarmarutilus rubilio inhabits various freshwater environments in three different ichthyogeographic districts. We investigated the genetic diversity of S. rubilio using two different mitochondrial markers (COI and CR), aiming to define its relationship with other similar taxa from the Balkan area and, from a phylogeographic perspective, test the effects of past hydrogeological dynamics of Italian river basins on its genetic structure and demographic history. Our analysis highlighted a marked genetic divergence between S. rubilio and all other roach species and, among Italian samples, revealed the existence of three deeply divergent geographic haplogroups, named A, B and C. Haplogroup C likely corresponds to a new putative cryptic species and is located at the northern border of the South European roach range; haplogroup B is restricted to Southern Italy; and haplogroup A is widespread across the entire range and in some sites it is in co-occurrence with C or B. Their origin is probably related to the tectonic uplifting of the Apuan Alps in the north and of the Colli Albani Volcano in the south during the Pleistocene, which promoted isolation and vicariance followed by secondary contacts.

A comprehensive DNA barcode inventory of Austria’s fish species

Austria is inhabited by more than 80 species of native and non-native freshwater fishes. Despite considerable knowledge about Austrian fish species, the latest Red List of threatened species dates back 15 years and a systematic genetic inventory of Austria’s fish species does not exist. To fulfill this deficit, we employed DNA barcoding to generate an up-to-date and comprehensive genetic reference database for Austrian fish species. In total, 639 newly generated cytochrome c oxidase subunit 1 (COI) sequences were added to the 377 existing records from the BOLD data base, to compile a near complete reference dataset. Standard sequence similarity analyses resulted in 83 distinct clusters almost perfectly reflecting the expected number of species in Austria. Mean intraspecific distances of 0.22% were significantly lower than distances to closest relatives, resulting in a pronounced barcoding gap and unique Barcode Index Numbers (BINs) for most of the species. Four cases of BIN sharing were detected, pointing to hybridization and/or recent divergence, whereas in Phoxinus spp., Gobio spp. and Barbatula barbatula intraspecific splits, multiple BINs and consequently cryptic diversity were observed. The overall high identification success and clear genetic separation of most of the species confirms the applicability and accuracy of genetic methods for bio-surveillance. Furthermore, the new DNA barcoding data pinpoints cases of taxonomic uncertainty, which need to be addressed in further detail, to more precisely assort genetic lineages and their local distribution ranges in a new National Red-List.

Minnow introductions in mountain lakes result in lower salmonid densities

Small fish species such as minnows (Phoxinus sp.) are introduced into mountain lakes by anglers that use them as live bait for fishing salmonids that were previously introduced in these naturally fishless habitats. Introduced fish severely impact native biota but minnows are nevertheless released believing to provide forage for game fish, i.e., salmonids. However, our results indicate that minnows negatively interact with game fish, reducing their relative densities. On some occasions, minnows can remain the only present fish following trout extinction. We believe that this information should be urgently disseminated among anglers as a pragmatic argument to also convince anglers less sensitive to conservation issues that carrying minnows to the mountains is not a good idea whatever the main interest is, e.g., nature conservation or outdoor recreation.

Molecular analysis reveals multiple native and alien Phoxinus species (Leusciscidae) in the Netherlands and Belgium

Fresh waters are among the most endangered ecosystems, one of the problems being the lack of data on biodiversity. In the center of the missing knowledge are cryptic species, two (or more) species classified as a single one due to their (seemingly) indistinguishable morphology. Lack of research and stabilizing selection are reflected in the cryptic diversity of the genus Phoxinus (Leusciscidae), the studies of which have intensified over the last two decades and reveal undetected taxonomic complexity. Moreover, some of the Phoxinus lineages act as invasive species, while others are endangered by their alien counterparts. Minnows have been intentionally (as food for predatory fish species) or unintentionally (with other fries) stocked causing hybridisation zones in Norway, Portugal, Spain, France, Italy, Germany and Austria. Given that genetic identity and lineage assignment of Phoxinus from Belgium and the Netherlands have not been researched, the goal of the study was to examine available samples from known localities in the area in order to infer- whether they are native or not. For this purpose, the barcoding region cytochrome oxidase I, another mitochondrial gene cytochrome b, a nuclear recombination activating gene 1 and a combination of these markers from a wider neighboring region were analyzed. The study found four different Phoxinus species/lineages occurring in Belgium and the Netherlands: P. phoxinus, P. csikii, P. septimaniae and genetic lineage 11 (possibly P.cf. morella). While the first seem to be native, the other three were probably introduced.