Five qualitative and seven quantitative colouration and spotting pattern features were measured in 23 brown trout Salmo trutta populations and two hatchery stocks. Simultaneously, the LDH-C1*, a diagnostic locus fixed for *90 and *100 alleles in stocking and native populations from southern Europe, respectively, was analysed to classify the brown trout studied according to their origin: native, hatchery stock and hybrids. The three genotypes showed significant differences in the colouration and spotting features and a discriminant function analysis could correctly identify 79% of the individuals. The most discriminating variables were dorsal fin margin colour, number of opercular spots, presence of the preopercular mark and diameter of black spots. Given the low cost, ease and possibility of field identification of native fish, the results indicate great opportunities for the application of morphological-based classification models on the conservation and management of native brown trout stocks. # 2005 The Fisheries Society of the British Isles

The genus Phoxinus is comprised of at least 15 currently recognized species inhabiting Eurasia. Morphological traits have been traditionally used to delineate species in Phoxinus; however, the high level of phenotypic plasticity observed in the genus has confounded this process. Molecular genetic analyses have revealed a higher than expected genetic structure within Phoxinus. Here, we analyzed both nuclear and mitochondrial molecular genetic markers to infer the phylogeography and divergence times of Phoxinus in the Iberian Peninsula. Our results show that the Iberian lineages of Phoxinus were polyphyletic. They also support the co‐existence of three species in the Iberian Peninsula, two corresponding to two previously recognized species (Phoxinus bigerri and Phoxinus septimaniae) and a third undescribed species (Phoxinus sp.). Phoxinus bigerri is structured into western Cantabrian, eastern Cantabrian, and Artibai basins. We hypothesize that this structure is a consequence of glaciation–deglaciation cycles during the Pleistocene. While the presence of P. septimaniae in the Iberian Peninsula is possibly the result of human translocation, that of Phoxinus sp. in lower Ebro rivers may be attributed to past fluvial captures. Our study represents the first report to show a relationship among Phoxinus populations from central Pyrenean rivers of Spain and France. Furthermore, we found genetic hybridization between Phoxinus sp. and P. septimaniae in the shared localities, a likely consequence of anthropogenic activities. Overall, our findings provide insight into the genetic structure of Iberian Phoxinus populations, including the presence of an undescribed species and the putative introduction of some species that may have implications for conservation.

Implementation of the Water Framework Directive requires tools for measuring and monitoring the ecological status of aquatic ecosystems. Several indices are in use in the Iberian Peninsula, although there has been little comparison among them. We sampled the fish assemblage and limnological features of the Tordera stream (NE Spain) quarterly from September 2001 to May 2003 to evaluate the usefulness of several fish metrics and to compare habitat quality and biotic indices currently in use. Data for eight biotic and abiotic indices for this and three other Catalan river basins were also compiled in order to analyse the relationships among indices. In the Tordera stream, fish abundance and richness increased with stream order except in the last sampling site that had the lowest fish abundance owing to the effects of drought and water abstraction. Although most indices were positively correlated, some displayed low or null correlations particularly for the Tordera basin which is more affected by water abstraction and less by pollution; a commonly used physico-chemical index (ISQA) was the least correlated. In a regional fish index (IBICAT) under development, the brown trout (Salmo trutta) has been previously considered as introduced in the Tordera basin. Here, we report an old published record that demonstrates that trout was present before 1845 and we argue that its status should be considered as uncertain given the current information available. Whether brown trout is treated as native or introduced to this river basin has profound effects on the results of fish metrics because of its dominance in the upper reaches. We briefly discuss the role of introduced species, particularly in headwater streams, in the development of fish indices. Our study exemplifies the need for careful, basin-specific assessment of native/introduced status in the development of fish metrics.

A multimetric Index of Biotic Integrity (IBI) based on fish data was developed to assess the ecological status of Iberian streams, in the context of the European Water Framework Directive. Fish assemblages were determined by electrofishing at 114 sites from 10 basins of the Júcar River Basin District. The sampled streams were typical Mediterranean streams with strong variation in flow, a species-poor and tolerant fish fauna, and low ecological specialization of the fish species. These features make it difficult to employ metrics based on species richness, trophic specialization, and reproductive strategy, which are typical of IBIs and similar indices. The proposed IBI (IBI-Jucar) is composed of five metrics related to fish health, age-structure, and abundance and richness of native and alien species. IBI-Jucar was validated by demonstrating high correlation with various measures of environmental degradation and with several biotic and habitat indices. It was also highly correlated with the European Fish Index (EFI+), despite different methods used for development and contrasting metrics obtained. The results underline the complementarity of different biotic indices and show that indices based on fish can be a valuable tool for determining environmental quality, even in species-poor Mediterranean streamsAdditional funding was provided by the Spanish Ministry of Science (CGL2009‐12877‐C02‐01 and Consolider‐Ingenio 2010 CSD2009‐00065

Summary Introduced species often thrive in modified systems, although it is not clear whether they have negative effects on native biota that might also be present or, alternatively, occupy niches that have been left empty due to the original habitat modification. We used 247 surveys of fish assemblages (48 species in all) in riverine reservoirs across the Iberian Peninsula to analyse the relationships between the species richness of introduced and native fish. Most of the samples (195) were from areas with a Mediterranean climate, while the reminder (52) had a temperate climate. Mediterranean reservoirs had more introduced than native species, with an opposite pattern in the temperate areas. The richness of non‐natives was positively related to the area of reservoir and human pressures and negatively related to altitude. Native richness was higher in larger and deeper reservoirs and lower in older and more impacted reservoirs, as well as in those with more introduced piscivores. There was a negative relationship between the richness of native fish and that of non‐native piscivores in Mediterranean reservoirs, confirmed through multiple regression and structural equation modelling. Contrastingly, native fish richness was mainly controlled by variables related to water quality in temperate areas, implying that the negative impacts of introduced fishes in reservoirs can be context dependent. The presence of introduced piscivores thus seems an important factor excluding many native fish from reservoirs in Mediterranean environments in the Iberian Peninsula.