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The abundance of European perch in Lake Piediluco has significantly dwindled in the last few years. The present study on diet overlap between perch and ruffe was prompted by the rapid expansion of the ruffe stock in the lake. This species was first found in the lake in 1996 and has since become one of the most abundant. The degree of diet overlap between the two species was analyzed by using data on the stomach contents of 275 European perch and 328 ruffe. Results are expressed as abundance (%N), occurrence (%S), weight percentage (%W) and index of predominance (Ip). The diet overlap index (α) was calculated by means of Schoener’s formula using the %W of each food item. As an estimate of the diet width of both species, we used Levins’ indexes of niche breadth (B) and standardized measurement of niche breadth (BA). Both species are strictly carnivorous, feeding mainly on invertebrates: the most important diet components were dipterans and crustaceans, but the European perch also feeds on fish. In the perch, the Levins index was greater (B=4.332) than that calculated for the ruffe (B=2.262). During the ontogenesis of the European perch, there is a rather pronounced diet shift: dipterans form the largest portion of the diet at all ages, though in older perch fish-eating becomes increasingly evident. Benthic crustaceans tend to be consumed in greater quantities by the 3+ age-class, though they are also found in the stomachs of specimens of all ages. Ruffe, by contrast, do not display a pronounced ontogenetic diet shift. The index of diet overlap between the two species was rather high, the maximum α value being 0.853; values indicate a high degree of diet overlap in the younger ageclasses (1+, 2+ and 3+), with a greater differentiation between the diets of the two species emerging as the age of the perch increased. Our research also clarified some of the biological characteristics of the European perch in Lake Piediluco, namely, theoretical growth in length, weight at length and relative weight. These analyses enabled us to compare the growth characteristics of the European perch during periods when ruffe stocks differed in terms of abundance. All of the results indicate that the growth conditions of the European perch population in Lake Piediluco are steadily worsening. This provides indirect confirmation of a negative interaction with the ruffe.

In this study we examine the spatial variations in the fish communities in the Tiber River watershed, including both native and exotic species. Its main objectives were to assess the quality of fish communities of this area and to verify if factors of fish community disturbance are constant over the basin or if they change along the river gradient. The level of degradation was evaluated according to the ratio between the number of native fish species and total number of species (ZIC = Zoogeographic Integrity Coefficient). A total of 37 fish species was found, 13 native and 24 exotic (64.86%). Cyprinid is the prevailing family with 15 species (7 native, 8 exotic). The species most frequently introduced are cyprinids, followed by salmonids (4 species) and gobids (3 species). Of the 24 exotic species only 11 (45.83%) can be considered intentionally introduced by man: the proportion of intentionally introduced transplanted species (66.67%) is considerably higher than the translocated species (33.33%). There is a correlation between the longitudinal gradient of the river, the morphological evolution of the riverbed and decline in water quality. High ZIC values were related to higher elevation, greater slope and better water quality. As the size of the river increases the fish communities appear to be ever-more dominated by species of exotic origin, whose number progressively increases with the worsening of the water quality and downstream movement. The number of native species is the greatest in the middle reaches of the rivers, and decreases both upstream and downstream. Compared to the introduced species, the native species tend to stay upstream and are often the only species found in the headwaters. The number of introduced species increases downstream. We have also found differences among translocated and transplanted species: the first ones tend to favor the middle reaches of the rivers, while transplanted species seem to prefer the downstream sectors. In almost all cases, the sampling station immediately below an impoundment has the lowest ZIC values in comparison to the river stretches above the dam. Our preliminary results suggest that characteristics of fish community alterations depend on the type of river sector involved; the small rivers of the basin are a refuge zone for the native community and are currently of fundamental importance for maintaining biodiversity.

The aim of this study was to gather more informations about the biological characteristics of Procambarus clarkii and to investigate the reasons of its rapid expansion in Lake Trasimeno. Specimens of both sexes (544 males and 624 females) were collected from October 2000 to November 2001. During the sampling period physical factors such as water temperature and hydrologic level of LakeTrasimeno were recorded. The study was conducted monthly in order to assess this species’ reproductive period. 1,168 specimens were analyzed for colour, sex, weight, and length. The sexual maturation of gonads was investigated in females. The results of this study evidenced that the population is in expansion, showing that Lake Trasimeno is an optimal habitat for this species.

The aim of this study was to gather information about the feeding habits of Micropterus salmoides Lac., an exotic species recently introduced into Lake Trasimeno and Esox lucius L., in order to determine the degree of overlap between the two diets. The stomachs of 179 largemouth basses and 125 pikes were examined. The index of diet overlap (α) was determined by using a Prominence Value (PV) of each food item, using Schoener’s formula. The value of the diet overlap index in the whole sample was 0.79. When the sample was divided in groups based on length, the index values were high and varied from a minimum of 0.623 to a maximum of 0.925. Based on theses results, a hypothesis of food competition between the two species in Lake Trasimeno could not be rejected.

The aim of this research was to assess the distribution, abundance and growth of the non-native topmouth gudgeon Pseudorasbora parva that was recorded for the first time in the Tiber River Basin (central Italy) in 1994. The competitive interaction of P. parva with four native fish species was also investigated. The study area comprised 92 watercourses of the Umbrian section of the Tiber River Basin. Demographic and environmental data were collected during the period 1990−2014 in 171 sampling sites. The results of this study showed a wide distribution of P. parva in the study area, with records from 23.39% of all sampling sites (40 out of 171). This species inhabits the downstream reaches, where the presence of many non-native species and the poor environmental quality are associated with a decrease in native fish species. A total of 5570 specimens of P. parva were collected and five age classes (0+ to 4+) were identified. The equation for the total length-weight relationship of P. parva was W = 0.021TL2.673±0.015. For the chub Squalius squalus, the Tiber barbel, Barbus tyberinus, and the roach, Rutilus rubilio, the average values of the relative weight were significantly higher in the sites where P. parva was absent. The results of the present study suggest the need to undertake proper strategies for native biodiversity conservation.

Padogobius bonelli is a goby native to Northern Italy, but several populations are established in Central Italy out of its native range. P. bonelli caused negative impact on native fish community but any study on growth in the introduced areas has ever been conducted. In this study age, growth and condition of a non-native population of P. bonelli from the River Aggia were investigated. Samples (n = 422) were collected monthly from January to December 2012. Age estimation was based on scalimetry and five age classes (0+–4+) were observed. Sex ratio was strongly male-biased. Growth in previous years was determined by back-calculation from scale measurements and the occurrence of Lee’s phenomenon was tested. Von Bertalanffy growth parameters were estimated (Males: L∞ = 8.35 cm, k = 0.40, Φ′ = 1.44; Females: L∞ = 8.71, k = 0.43 , Φ′ = 1.51). No differences in growth between sexes were observed, despite sexual dimorphism based on the larger size of males is count as a typical trait of the species. This result could be affected by the reverse Lee’s phenomenon that acts only on females, since in the population selectively survived females of larger size. Smaller females would be disadvantaged, especially during the breeding season, as highlighted by the low somatic condition observed in the period April–June.

The introduction of exotic fish species in the river Tiber basin has probably caused a serious alteration of original faunal composition. The purpose of this research was to assess the changes occurred over time in the state of the fish communities with particular reference to the reduction of local communities of endemic species. The study area comprised 68 watercourses of the Umbrian portion of the River Tiber basin; the analyses were carried out using the data of the Regional Fish Map of 1st and 2nd level and the 1st update, respectively collected during the periods between the 1990–1996, 2000–2006 and 2007–2014, in 125 sampling stations. The results show a progressive alteration of the fish communities’ structure, as confirmed by the appearance in recent times of new alien species. A total of 40 species was found, only 14 native. The qualitative change of the fish communities appear to be closely related to the longitudinal gradient of the river. The results shows that particularly in the downstream reaches, the combined action of pollution and introduction of exotic species resulted in a gradual decrease in the indigenous component of fish communities. The information collected are the indispensable premise for taking the necessary strategies for conservation of endangered species.

The age, growth and body condition of the big-scale sand smelt (Atherina boyeri) population of Lake Trasimeno were investigated. In total, 3998 specimens were collected during the study and five age classes (from 0+ to 4+) were identified. From a subsample of 1017 specimens, there were 583 females, 411 males and 23 juveniles. The equations between total length (TL) and weight (W) were: log 10W = −2.326 + 3.139log 10TL for males and log 10W = −2.366 + 3.168log 10TL for females. There were highly significant differences between the sexes and for both sexes the value of b (slope of the log (TL-W regression) was greater than 3 (3.139 for males and 3.168 for females), indicating positive allometric growth. The parameters of the theoretical growth curve were: TLt = 10.03 cm; k = 0.18 yr-1, t0 = − 0.443 yr and Φ′ = 1.65. Monthly trends of overall condition and the gonadosomatic index (GSI) indicated that the reproductive period occurred from March to September. Analysis of back-calculated lengths indicated the occurrence of a reverse Lee’s phenomenon. This could be a symptom of predation or competition, with consequences for young specimens with slower growth and smaller size.

The analysis of catch selectivity of fishing equipment is a crucial step for the management of alien species in freshwater ecosystems. Roach Rutilus rutilus was introduced in many waterways in Italy often becoming the dominant species of the fish community and it is now considered potential pest. In Piediluco lake the species was first found in 2004 and its abundance has increased at a level that creates concern for the other fish species present in the lake. The growth of R. rutilus and the selectivity of gill-nets on its population were examined in Piediluco lake by analysing the selectivity of gill-nets of different mesh size. Sampling was conducted from January 2011 to October 2012 by means of gill-nets of different-sized mesh (8, 10, 12.5, 15.5, 19.5, 24, 28, 35, 45 and 55 mm). The results showed that R. rutilus in Piediluco lake had a growth faster and higher than in many other lake environments. The results of gill-nets selectivity gave important information to design a plan to control this species and confirmed that the use of suitable fishing techniques could be useful to manage the population of this alien species in Piediluco lake as well as in other similar environments.

Squalius lucumonis (Bianco, 1983) is an endemic species restricted to three river basins in central Italy and listed as endangered according to IUCN Red List. The aim of this research was to increase the information on ecological preferences of this species and to focus on its differences with S. squalus (Bonaparte, 1837). Data collected in 86 different watercourses throughout Tiber River basin were analysed in the research. For each of the 368 river sectors examined, the main environmental parameters and the fish community were considered. The information were analysed by means of the Canonical Correspondence Analysis (CCA) while the differences in ecological traits between S. lucumonis and S. squalus were compared by ANOVA. The results of the study showed significant differences in the ecological preferences of the two species: the S. lucumonis showed predilection for smaller watercourses characterised by a lower number of species and a higher degree of integrity of fish community than S. squalus This information allowed to increase the basic knowledge on population biology and ecology of S. lucumonis that could be very useful for the management and conservation of this Italian endemic species.

Growth and some reproductive properties of native Tinca tinca Linnaeus, 1758 from Trasimeno Lake were investigated during 2009 and 2010. The total sample of fish (510) was composed by 126 males, 221 females and 163 immature specimens. Total length (TL ± 0.1 cm) and weight (W ± 0.1 g) were recorded; age estimation was based on scalimetry and sex was determined by microscopic observation of the gonads. Age composition varied from 1+ to 11+ . The TL-W relationship was log 10W = −2.235 + 3.248log 10TL. Previous growth was determined with back-calculation from scale measurements using the Fraser-Lee method. Theoretical length growth was estimated with von Bertalanffy’s model. Analysis of the gonadosomatic index (GSI) suggests that the reproductive period of the population took place from May to July. Sexual maturation occurred in both sexes at the second year of life. The mean diameter of eggs was 0.075 mm. The mean number of eggs produced by each female was 233 930 and increased with the size of the specimens. Though it is one of the most widespread and interested species in fishing in Italian waters, tench has not been widely studied; this research deepens some biological characteristics of this species that is strongly shrinking in Italy.

The aim of the research was to test relative weight (Wr), a condition index which allows evaluation of fish well-being, as a tool to investigate the impact of the presence of non native species (NNS) on the condition of the key native species (NS) of the Tiber River basin (Italy): Barbustyberinus Bonaparte, Leuciscus cephalus (Linnaeus), Leuciscus lucumonis Bianco, Rutilus rubilio (Bonaparte) and Telestes muticellus (Bonaparte). By means of Canonical Correlation Analysis, data from 130 sampling sites, distributed throughout Tiber River basin, were examined. Wr of NS was related to densities of NNS and to environmental variables. Moreover, the correlation between Wr of NS and density of NNS was investigated through linear regression analysis and covariance analysis. Preliminary results encourage the use of Wr as a tool to assess the relationship between NS and ecological factors (such as the presence of NNS) and to explain the changes that occur along the longitudinal gradient of a river.

This study investigated the reproductive properties of the population of chub Squalius squalus (Linnaeus, 1758) in the Assino creek, one of the largest tributaries of the upper course of the River Tiber. A total of 547 specimens were caught monthly from March 2008 to May 2009. The age composition of the sample ranged between 0+ and 11+. The sample was made up of 64.54% males and 35.46% females; sexual maturity was attained in both sexes in the second year of life. Analysis of the gonado-somatic index (GSI) and of the stage of gonad maturation throughout the year suggests that the reproductive period of the population extends over a long time (April–July). The relationship between total length and fecundity was F = 5.466TL2.312. The mean number (±SE) of eggs produced by each female was 15 351 ± 1705 and increased with the size and age of the specimens; with regard to relative fecundity, an average value (±SE) of 53 553 ± 4098 eggs·kg-1 was observed. The mean diameter (±SE) of ripe eggs was 0.117 ± 0.004 cm. This study sheds light on some important characteristics of the reproductive biology of the chub that have not been fully investigated in Italian populations.

In this study, the population structure, growth parameters and condition of chub, Squalius squalus, from the Assino Creek, a tributary of the River Tiber, were investigated. A total of 1311 specimens were caught monthly from March 2008 to May 2009 by electrofishing. Total length (TL ± 0.1 cm) and weight (W ± 0.1 g) were recorded; age estimation was based on scalimetry and sex was determined by macroscopic observation of the gonads. Age composition ranged from 0+ to 11+ . Total length varied from a minimum of 4.1 cm to a maximum of 48.8 cm, for a weight of 0.5 g and 1233.0 g, respectively. Length-weight regression was log 10W = −2.201 + 3.127log 10TL for males and log 10W = −2.273 + 3.190log 10TL for females. Previous growth was determined with back-calculation from scale measurements using the non-linear Body Proportional Hypothesis. Theoretical length growth was estimated with von Bertalanffy’s model. Condition was evaluated by relative weight. In Italy there are few available data about the biology of Squalius squalus: the aim of this study was therefore to fill this lack of information by investigating some important aspects of the growth of the population in Assino Creek.

The purpose of this study was to provide reference data on the growth and population structure of brown trout Salmo (trutta) trutta Linnaeus, in Central Italy. Standards for growth (percentiles and a standard growth model) were developed from the von Bertalanffy growth model by using length-at-age data obtained from 122 sampling sites in the River Tiber basin. Length-frequency indices provide a numeric estimation for deviations of the population structure from a balanced population. We adapted the traditional North American Relative Stock Density (RSD) and Proportional Stock Density (PSD) indices to brown trout populations in Central Italy by means of two methods. In the first method, the benchmarks of length categories were established by using percentages applied to the largest individual in the dataset. 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 263 sampling sites in the River Tiber basin. The results showed that the PSD calculated by the first method provided a better insight into the population structures of brown trout. These results provide tools that will help ichthyologists and fish managers to compare the growth and population structure of brown trout throughout Central Italy.

The fishery biology of the goldfish Carassius auratus was studied in Lake Trasimeno by analysing the selectivity of the equipment that can be used to control this invasive species. Sampling was conducted monthly from February 2003 to January 2004 by means of electrofishing, fyke-nets and gill-nets of different-sized mesh (22, 25, 28, 35, 40, 50, 70 and 80 mm). The average value of the CPUEs of goldfish caught was 10175.48 g·10−2·m−2 for gill-nets, 246.97 g·h−1 for fyke-nets and 606.50 g·min−1 for electrofishing. The efficiency of electrofishing was not uniform in all periods of the year, the mean CPUEs being highest in spring, when specimens of reproductive age were preferentially caught. Gill-nets yielded abundant catches of goldfish in all seasons, and displayed good sampling efficiency even in winter. With regard to the selectivity of gill-nets, estimated optimum selection lengths for each mesh size were: 11.92 cm, 13.55 cm, 15.18 cm, 18.97 cm, 21.68 cm, 27.10 cm, 37.94 cm and 43.36 cm. The results of this research demonstrate that the various fishing techniques can be effectively combined with the aim of controlling the goldfish population in Lake Trasimeno.

The age and growth of the invasive black bullhead Ameiurus melas (Rafinesque, 1820) were studied in the Corbara Reservoir, an artificial lake located on the River Tiber in central Italy. The results of the research revealed that the population was made up of eight cohorts, the oldest specimens being spawned in 1999. The sex ratio appears to be balanced, although females predominate in the younger cohorts, while the percentage of males increases among older specimens. The differences between sexes in the slope of the length-weight relationship were not statistically significant; the slope for the whole sample (b = 3.055) was significantly greater than 3, indicating an allometric growth pattern of the black bullhead. There were no significant differences in mean back-calculated lengths at age between the sexes. Analysis of Lee’s phenomenon revealed the existence of differential mortality among younger individuals (1 and 2 years old) that favours larger individuals. The Von Bertalanffy growth function was TLt = 35.69 {1 – exp[–0.18 (t + 0.27)]}. The specimens caught displayed mean relative weight (Wr) values distinctly below 100 at all ages, while no significant difference emerged between the sexes with regard to condition.