Seven sites on three tributaries with intermittent flow regimes in the middle reaches of the Guadiana, i.e. Xévora, Caia and Degebe, were sampled approximately every 3 months from April 1995 to April 1997. The density and biomass of fish were greater in downstream rivers and sites. Along the Xévora River, a series of point abundance samples showed evidence of fish zonation along the river. Canonical correspondence analysis (CCA) suggested a simple relationship between the different species and their preferred habitat. The small‐sized Rutilus alburnoides and Leuciscus pyrenaicus used most or all of the habitats with some cover and flowing water. Greater concentrations of larger fish were found in downstream reaches which generally had greater depths as stream width increased: large Barbus microcephalus, B. steindachneri and B. comiza preferred such sites on the Degebe River. Droughts in seasonal Mediterranean streams such as the Guadiana River are a predictable natural disturbance. In the summer, flow ceases and some stretches of river consist of isolated pools. This results in intense aggregations of fish and possible competition for food and/or space. Although some species are well adapted to natural droughts, habitat degradation and possibly the introduction of exotic species contribute to marked variability in species composition.

Neighbour-joining and parsimony analyses identified five lineages of cyprinids: (1) European leuciscins (including Notemigonus)+North American phoxinins (including Phoxinus phoxinus);(2) European gobionins+Pseudorasbora; (3) primarily Asian groups [cultrins+acheilognathins+ gobionins (excluding Abbotina)+xenocyprinins]; (4) Abbottina+Sinocyclocheilus+Acrossocheilus;(5) cyprinins [excluding Sinocyclocheilus and Acrossocheilus]+barbins+labeonins. Relationships among these lineages and the enigmatic taxa Rhodeus were not well-resolved. Tests of monophyly of subfamilies and previously proposed relationships were examined by constraining cytochrome b sequences data to fit previous hypotheses. The analysis of constrained trees indicated that sequence data were not consistent with most previously proposed relationships. Inconsistency was largely attributable to Asian taxa, such as Xenocypris and Xenocyprioides. Improved understanding of historical and taxonomic relationships in Cyprinidae will require further morphological and molecular studies on Asian cyprinids and taxa representative of the diversity found in Africa.

The hybrid minnow Squalius alburnoides comprises diploid and polyploid forms with altered modes of reproduction. In the present paper, we report a cross where a triploid female generated both large, triploid and small, haploid eggs simultaneously, which were fertilized with S. pyrenaicus sperm. Although the large eggs were rarer (15%), they originated offspring with higher survivorship, so that tetraploids were dominant among the surviving siblings. The cross yielded apparently all female progeny. Inheritance patterns were inferred using four microsatellite markers and NORs (Nucleolus Organizer Regions) phenotypes, and suggested that haploid eggs were probably produced by an atypical hybridogenesis, in which the elimination of the unmatched genome permitted random segregation and recombination between the homospecific genomes, while the triploid eggs were clonal. The present results suggest that the occurrence of triploid unreduced eggs may be a new route for the natural tetraploidization in the complex.

The description of two new Portuguese freshwater fish species is presented. Leuciscus torgalensis occurs in the Mira basin and Leuciscus aradensis in the Arade basin and in two other small southern basins. The type material is deposited in the collections of the Museu Bocage, Lisbon (MB). The general external similarity between L. torgalensis and L. aradensis and two further species, L. carolitertii and L. pyrenaicus is high. The main external diagnostic character for both new taxa is the lower number of scales of the lateral line, despite the slight differences between them. Head form is a distinctive character between the two new species; such that head width is greater in L. aradensis. Distinct osteological characters between both L. torgalensis and L. aradensis and the other Iberian Leuciscus species are: the supraorbital canal and the modal vertebral formula that are shorter and lower in the new species, respectively. The preopercular-mandibular canal communication exists in L. aradensis, but not in L. torgalensis. Allozyme and mitochondrial DNA data also supported a monophyletic clade of Mira and Arade and the distinction of the two new species. The differentiation of the new species occurred either by an early isolation of the Mira and the Arade basins or by ecological conditions after the disjunction of all basins in Portugal, during the early Quaternary. 1998 The Fisheries Society of the British Isles

Rutilus alburnoides complex is a common and widely distributed Iberian cyprinid, whose natural populations include mainly diploid and triploid forms. The Guadiana populations of R. alburnoides were studied to determine whether habitat segregation and morphological differences exist between these forms. The ploidy level of each specimen was determined by measuring erythrocyte DNA content using flow cytometry. Evidence of spatial segregation between diploid males and the two female forms was found. Diploid males were best represented in the River Degebe, which was shallow, with higher temperatures (especially during the spring and summer), and silt and sandy substrate. Diploid females were found in deeper water, on steeper gradients and coarse substrata, while triploid females preferred higher current velocity and a high proportion of instream cover, especially during the spring. The ecological differences may reduce competitive interactions, and should promote a stable coexistence of the different forms. Morphological distinction between fish of different ploidy levels was not established, but differences were found between the males and females. Discriminant analysis allowed, with a 10% error, the separation of both sexes through six morphological characteristics that could be recorded in the field. 1998 The Fisheries Society of the British Isles