RAPD and isoenzyme analysis of genetic variability in three allied species of cat®sh (Siluriformes: Pimelodidae) from the Tibagi River, Brazil Fernanda Simo Ä es de Almeida, Maria Helena Pelegrinelli Fungaro and Leda Maria Koelblinger Sodre Â* Departamento de Biologia Geral, Centro de Cie Ãncias Biolo  gicas, Universidade Estadual de Londrina, Campus Universita  rio, Caixa Postal 6001, 86051-990, Londrina, Parana Â, Brazil (Accepted 1 December 1999) Abstract Genetic variability in three species of Pimelodidae cat®sh (Iheringichthys labrosus, Pimelodus maculatus and Pimelodus cf. absconditus), collected at four sites in the Tibagi river-basin: Sertaneja, Londrina (lower Tibagi), Sapopema (middle Tibagi) and Tibagi (upper Tibagi) was analysed using RAPD and isoenzymatic techniques. Iheringichthys labrosus had the greatest genetic variability showing a proportion of mean polymorphic loci (P Å m) of 53.7%. The dendrogram showed that the individuals from the locations were clustered together, supporting the hypothesis that I. labrosus has a sedentary or localized geographical distribution. Pimelodus maculatus is the only species studied that is considered to be highly migratory. The P Å m obtained for this species was 30.2%. Their genetic dendrogram showed that the individuals were not clustered, based on the place of collection. P. cf. absconditus had a P Å m value of 47.4%, and the external morphology of this species is similar to that of I. labrosus, which hindered differentiation of individuals from the two species. RAPD and isoenzyme analysis, however, provided differential patterns for P. cf. absconditus from I. labrosus. Key words: RAPD, isoenzyme, Pimelodidae, genetic variability INTRODUCTION Several investigations in the last 25 years have made use of allozyme analysis to measure parameters such as genetic variability in natural populations and gene ¯ow among populations, processes of natural hybridization, species dispersion and phylogenetic analysis in animals, plants and micro-organisms (cf. Ferguson et al., 1995). The introduction of polymerase chain reaction (PCR) by Mullis & Faloona (1987) has led to the development of powerful techniques to detect DNA polymorphism such as the PCR-derived technique of random ampli®ed polymorphic DNA (RAPD). This technique is based on the observation that single DNA primers of an arbitrary nucleotide sequence can amplify genomic DNA sequences during a PCR whenever they locate regions of suf®cient homology at a favourable distance and in converging orientations on the two DNA strands (Welsh & McClelland, 1990; Williams et al., 1990). This method has been successfully applied to assess genomic varia- bility in several marine ®sh (Bielawski & Pumo, 1997; Elo et al., 1997; Jayasankar & Dharmalingam, 1997). South America has the richest freshwater ichthyo- fauna in the world. Representative groups of primitive, cartilaginous ®sh and an in®nity of bony ®sh are found on this continent, but many species remain insuf®ciently described because of this great diversity. There are no inventories on the natural state of the fauna, or scienti®c surveys that document the different effects of agents that alter the aquatic environment, such as agricultural run-off, erosion, deforestation and storage dams, and the development of conservation strategies for aquatic ecosystems to ensure the preservation of rare or threatened species have been hindered (UEL/COPATI/ KLABIN, 1991). The Tibagi river-basin, located in the state of Parana Â, Brazil, is a rich hydrographical net with 65 main branches and hundreds of smaller tributaries. The area of the river-basin is c. 26 000 km 2 and covers 13% of the surface of the state (cf. Bennemann et al., 1995). The Pimelodidae family is large and morphologically diverse, with > 300 species distributed in about 60 genera throughout all Central and South America, and it is economically signi®cant as a food source (Burgess, 1989). Bennemann et al. (1995), surveyed ®sh fauna at ®ve sampling points along the Tibagi River, and found the following Pimelodidae species: Iheringichthys labro- sus, Pimelodus maculatus, Pseudopimelodus cf. zungaro, Pseudoplatystoma coruscans, Steindachneridion sp., *All correspondence to: L. M. K. Sodre Â. E-mail: leda@uel.br J. Zool., Lond. (2001) 253, 113±120 # 2001 The Zoological Society of London Printed in the United Kingdom