The aim of the research was to test relative weight (W r ), 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): Barbus tyberinus 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. W r of NS was related to densities of NNS and to environmental variables. Moreover, the correlation between W r of NS and density of NNS was investigated through linear regression analysis and covariance analysis. Preliminary results encourage the use of W r 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. RÉSUMÉ Évaluation de l'impact des poissons d'eau douce non indigènes sur les espèces indigènes utilisant le poids relatifLe but de cette recherche était de tester le poids relatif (W r ), un indice de condition qui permet l'évaluation du bien-être des poissons, comme outil pour étudier l'impact de la présence d'espèces non indigènes (NNS) sur l'état des espèces natives clés (NS) du bassin du Tibre (Italie) : Barbus tyberinus Bonaparte, Leuciscus cephalus (Linné), Leuciscus lucumonis Bianco, Rutilus rubilio (Bonaparte) et Telestes muticellus (Bonaparte). Par le biais de l'analyse de corrélation canonique, les données de 130 sites d'échantillonnage, répartis tout au long du bassin de la rivière Tibre, ont été examinés. Le W r des NS a été relié à des densités de NNS et aux variables environnementales. Par ailleurs, la corrélation entre W r des NS et de la densité de NNS a été étudiée par analyse de régression linéaire et analyse de covariance. Les résultats préliminaires incitent à l'utilisation de W r comme un outil pour évaluer la relation entre les NS et les facteurs écologiques (tels que la pré-sence de NNS) et pour expliquer les changements qui se produisent le long du gradient longitudinal d'une rivière.
External morphology in black bullhead Ameiurus melas, a fish species considered to have high invasive potential, was studied in its four non-native European populations (British, French, Italian and Slovak). The aim of this study was to examine this species' variability in external morphology, including ontogenetic context, and to evaluate its invasive potential. Specimens from all non-native populations reached smaller body size compared to individuals from native populations. 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. Specimens from the U.K., Slovak and French populations appeared to be rather similar to each other, whereas the Italian population showed the most distant phenotype. This probably results from the different thermal regime in the Italian habitat. Ameiurus melas from non-native European populations examined in this study showed some potential to alter the body shape both within and between populations. The phenotypic plasticity of A. melas, however, was not found to be as significant as in other invasive fish species. The results suggest that morphological variability itself is not necessarily essential for invasive success. The invasiveness of A. melas is therefore probably favoured by variations in its life-history traits and reproduction variables, together with some behavioural traits (e.g. voracious feeding and parental care) rather than by phenotypic plasticity expressed in external morphology.
Key-words:Population dynamics, Lee's phenomenon, fishery management, introduced species, Lake TrasimenoThe 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 10 W = −2.326 + 3.139 log 10 TL for males and log 10 W = −2.366 + 3.168 log 10 TL 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: TL t = 10.03 cm; k = 0.18 yr −1 , t 0 = −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. L'analyse des longueurs rétro-calculées indique la présence d'un phénomène de Lee inversé. Ce pourrait être un symptôme de la prédation ou de la concurrence ayant des conséquences sur les jeunes spécimens à croissance plus lente et de plus petite taille.
Data on length and weight of Aegean chub Squalius fellowesii, an endemic species distributed in the Aegean drainages of Anatolia, Turkey, were used to calculate a standard weight (Ws) equation by means of the empirical percentile (EmP) method. The resulting Ws equation was log10 Ws = −3.801 + 1.783·log10TL + 0.329·(log10TL)2. Over the range of application (70–220 mm TL), the EmP Ws equation was not biased by length, and the use of this equation is suggested as a way to calculate the relative weight (Wr) of Aegean chub throughout the species’ distribution area. Received June 12, 2012; accepted July 27, 2012
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