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In running waters, under climate change conditions, the combined effect of water warming and decreasing flow rates may encourage colonisation by invasive cool and warm-water fish species. The aim of the study was to analyze the potential climate change effects on the spread of four invasive alien fishes in the Tiber River basin, taking into account the effects of river fragmentation. Fish and environmental data collected in 91 sites over the years 1998–2018, were used to analyze temporal changes in their habitat requirements. A multivariate analysis was conducted, and the hypothesis of a range expansion towards the upstream reaches has been tested. For Barbus barbus, Gobio gobio, Padogobius bonelli and Pseudorasbora parva population abundances and body condition were analyzed. Detectability, occupancy, local extinction and colonization probabilities were estimated. We showed that B. barbus and P. bonelli have significantly extended their range toward upstream. P. parva did not move toward higher altitudes significantly, suggesting that, at this stage, the species has probably reached an equilibrium. River fragmentation, elevation, water temperature and average current speed seem to be major determinants in colonization processes, affecting the dispersal ability of the species. Not surprisingly for species introduced in relatively recent times, the colonization probabilities were much higher than extinction probabilities. Our results provided evidence for some synergistic effects between climate changes and alien fish species invasions, in terms of species range shifts mediated by rising water temperatures, although they should be interpreted cautiously, taking into account that these species most likely were not yet stabilized. [ABSTRACT FROM AUTHOR]

Salmonids inhabiting Mediterranean rivers are of particular concern for biodiversity conservation, as they are threatened by various stressors, including habitat alterations, overfishing, climate change, and introgressive hybridization with alien species. In the Tiber River basin (Central Italy), genetic introgression phenomena of the native Salmo cettii with the non‐native Salmo trutta hinder the separate analysis of the two species, which are both included in the S. trutta complex. Little is known about the factors currently limiting the trout populations in this area, particularly with respect to climate change. With the intention of filling this gap, the aims of the current study were to (a) quantify changes in the climate and (b) analyze the distribution, status, and ecology of trout populations, in the context of changing abiotic conditions over the last decades. Fish stock assessments were carried out by electrofishing during three census periods (1998–2004, 2005–2011, and 2012–2018) at 129 sites. The trend over time of meteorological parameters provided evidence for increased air temperature and decreased rainfall. Multivariate analysis of trout densities and environmental data highlighted the close direct correlation of trout abundance with water quality, altitude, and current speed. Climate‐induced effects observed over time in the sites where trout were sampled have not yet led to local extinctions or distribution shifts, indicating a marked resilience of trout, probably due to the buffering effect of intrinsic population dynamics. Decreasing body conditions over time and unbalanced age structures support the hypothesis that variations in hydraulic regime and water temperature could overcome these compensatory effects, which may lead to a severe decline in trout populations in the near future. In a climate change context, habitat availability plays a key role in the distribution of cold‐water species, which often do not have the possibility to move upstream to reach their thermal optimum because of water scarcity in the upper river stretches. [ABSTRACT FROM AUTHOR]

Global climate changes have led to a gradual warming of the planet, resulting in decreased precipitation and rising temperatures in Mediterranean inland waters. In Trasimeno Lake, the largest shallow lake in Italy, some non‐native fish species have probably benefited from these changes as they are thermophilic and characterised by wider habitat preferences. Fish data collected by gillnets and fyke nets between 1956 and 2016, and by electrofishing in 1993 and 2014, were used to analyse changes over time in the fish community in relation to environmental conditions. An explosion in goldfish Carassius auratus (L.), following its introduction in 1988, coupled with water level fluctuations and reduced transparency, contributed to the reduction in commercial fish catch in the lake, and to the decline of the endemic southern pike Esox cisalpinus Bianco & Delmastro, already threatened by reduced spawning habitat and interspecific competition with other non‐native predatory fishes. [ABSTRACT FROM AUTHOR]

The purpose of the research was to analyse the distribution, abundance and growth of Carassius spp., a taxon which includes non-native species introduced into the water bodies of the Umbrian portion of the Tiber River basin during the late 1980s. Additionally, the study estimated the relative weight for Barbus tyberinus, Squalius lucumonis and Sarmarutilus rubilio to investigate the presence of competitive interactions between Carassius spp. and these native species that characterize the middle and lowland reaches of the Umbrian watercourses. Currently, Carassius spp. is widely distributed in both the stagnant and the slow-running waters of the entire basin. The presence of these species was recorded in 34.81% of the total sampling sites; the results showed that the presence of Carassius spp. was associated with the presence of other non-native species and with poor water quality. In total, 4520 specimens of Carassius spp. were collected and the age composition ranged from 0+ to 9+. The equation for the length-weight relationship (TL-W) was determined as W = 0.010TL3.180. For the Etruscan chub Squalius lucumonis, an endemic species of central Italy, the mean value of the relative weight was significantly higher when Carassius spp. was absent. The results of the research suggest the need to establish effective management conservation strategies for this endemic species. [ABSTRACT FROM AUTHOR]

Stock-density indices are standardized methods for analyzing length-frequency data that quantify the length structure of a fish population into length categories that are of interest to recreational anglers. We adapted North American relative stock density (RSD) and proportional stock density (PSD) indices to four Italian endemic or native cyprinid species by means of two methods. In accordance with the traditional approach, the benchmarks of length categories were established according to Gabelhouse's percentage classification and calculated on the basis of the largest individual in the data set for each species. In the second method, asymptotic length and size at maturity were used to define the length categories for index calculation. Both methods were tested on length-frequency data from fish collected from sampling sites in the Tiber River basin. The results showed that the traditional approach displayed better applicability, required less sampling effort, and provided a better insight into the length structure of the fish populations studied. [ABSTRACT FROM AUTHOR]

The article discusses a study which analyzed the growth and reproductive biological features of the invasive goldfish Carassius auratus auratus from Lake Trasimeno in Umbria, Italy and provided a view to drawing up plans for a population control. Results showed the eight age-classes of the study population with an extremely unbalanced sex ratio, rapid growth and absence of sexual dimorphism in growth. The researchers determined the existence of an inverse Lee phenomenon among one-year old specimens based on findings from back-calculation analysis. The study observed that sexual maturity was reached after the second winter of life but only 7.55 percent of females were reproductive at this age while 60.61 percent attained sexual maturity in the first year.

Climate changes will lead to a worsening of the ecological conditions, in terms of hydrological instability and rising water temperatures, of the Mediterranean rivers. Freshwater fishes inhabiting this area can be threatened in the near future by accelerating drought and decreased ecological connectivity. The main aim of the research was to analyze changes in the distribution of the endemic freshwater fishes Padogobius nigricans, Squalius lucumonis and Telestes muticellus in the Tiber River basin (Italy), within a proven period of climate warming, in terms of increasing water temperature and droughts. A multivariate analysis was conducted using fish and environmental data collected in 117 sites over the years 1990–2017. For the three species, population abundance, age structure and body condition were analyzed. Detectability, occupancy, local extinction and colonization processes were also examined. We showed that S. lucumonis and T. muticellus have shifted their distributions upstream, likely in order to reach their thermal optimum. Padogobius nigricans did not move upstream significantly, since the species is characterized by limited vagility and thus a low dispersal capability in a context of high river fragmentation. In the study area, elevation and river barriers seem to play a key role in extirpation and colonization processes; for S. lucumonis and T. muticellus the extinction probability decreased with increasing altitude, while for P. nigricans the colonization probability decreased with an increasing degree of river fragmentation. These results highlight how species-specific dispersal ability can lead to varying adaptability to climate change. [ABSTRACT FROM AUTHOR]