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.
Relative weight (W r ) is an important and commonly used condition index that provides a measure of the well-being of a fish population by comparing the actual weight of a specimen with the ideal weight of a specimen of the same species and of the same length in good physiological condition, i.e. the standard weight (W s ). Two methods of calculating the standard weight are proposed in the literature: the RLP method and the EmP method. The aim of this study was to develop a standard weight equation for European perch by means of both methods, using length-weight data from 64 913 fish from 18 countries (across Europe and Oceania). The resulting equations were: log 10 (W s ) = )3.1483 + 1.2663 log 10 (TL) + 0.4291 [log 10 (TL)] 2 for the EmP method and log 10 (W s ) = )5.3493 + 3.2152 log 10 (TL) for the RLP method. The applicable length-range of the two W s equations was restricted to 80-460 mm. A further research aim was to compare the performances of RLP and EmP. The resulting quadratic EmP W s equation did not exhibit length-related biases, which suggests that it can be used to compute relative weight for European perch.
Relative weight (Wr) is an index of condition that enables evaluation of the well‐being of fish by comparing the actual weight of a specimen with the ideal weight of a specimen of the same species and the same length that is in good physiological condition (i.e., the standard weight [Ws]). This index was primarily developed to assess the status of sport fishes. Recently, however, many authors have encouraged the use of this index as a fisheries assessment tool for nongame species as well, especially those that are endangered or threatened. Length and weight data on brook chub Squalius lucumonis, an Italian endemic species listed as endangered by the International Union for the Conservation of Nature, were collected across its area of distribution and used to compute a standard weight (Ws) equation by means of the empirical percentile method. The Ws equation thus obtained (log10 Ws = –7.75 + 5.75 log10[total length {TL}] – 0.66 [log10TL]2; TL range of application = 90–210 mm) was not biased by length and is recommended as a way to compute Wr for brook chub. Received October 11, 2011; accepted January 12, 2012
Key-words:von Bertalanffy's parameters, back calculation, reproduction, fecundity, gonadosomatic index 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 10 W = −2.235 + 3.248 log 10 TL. 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. La longueur totale (TL ± 0,1 cm) et le poids (W ± 0,1 g) ont été enregistrés ; l'estimation de l'âge a été faite par scalimétrie et le sexe a été déterminé par l'observation microscopique des gonades. La composition en âge variait de 1+ à 11+. La relation TL-W était log 10 W = −2, 235 + 3,248 log 10 TL. La croissance a été détermi-née par rétro-calcul à partir de mesures sur les écailles en utilisant la méthode de Article published by EDP Sciences L. Pompei et al.: Knowl. Managt. Aquatic Ecosyst. (2012) 406, 07 Fraser-Lee. La croissance en longueur théorique a été estimée avec le modèle de von Bertalanffy. L'analyse de l'indice gonadosomatique (GSI) suggère que la période de reproduction de la population a lieu de mai à juillet. La maturation sexuelle a eu lieu dans les deux sexes dès la deuxième année de vie. Le diamètre moyen des oeufs était de 0,075 mm. Le nombre moyen d'oeufs produits par chaque femelle était 233 930 et augmentait avec la taille des spécimens. Bien qu'elle soit l'une des espèces les plus répandues et recherchées par la pêche dans les eaux italiennes, la tanche n'a pas été largement étudiée ; cette recherche approfondit certaines caractéristiques biologiques de cette espèce qui est en forte régression en Italie. RÉSUMÉ
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