fisman0101 Fisheries Management and Ecology 1997, 4, 83–91 Diet and feeding relationships of two Iberian cyprinids M.M. COELHO, M.J. MARTINS, M.J. COLLARES-PEREIRA & A.M. PIRES Departamento Zoologia e Antropologia, Universidade de Lisboa, Portugal I.G. COWX University of Hull, International Fisheries Institute, UK Abstract The diet and feeding interactions of the Iberian roach, Rutilus alburnoides (Steindachner), and chub, Leuciscus pyrenaicus Gu ¨nther, were studied in the Sorraia river system. Seasonal shifts in the diets were examined to determine trophic overlap between the two species. Dipteran larvae were the dominant item in the diet of roach with the exception of summer and early autumn when dipteran adults became important. Ephemeroptera nymphs and imagos were the two principal food categories in chub diet. Plant material and terrestrial insects were consumed by both species mostly in the summer and autumn, periods of low availability of aquatic invertebrates in temperate streams. A low dietary overlap was found, probably resulting from differences in their seasonal foraging activity, but also from a compromise between the consumption of highly abundant plant material and rare animal food items. KEYWORDS: community structure, diet, feeding overlap, Leuciscus pyrenaicus, Portugal, Rutilus alburnoides. Introduction Although cyprinid fish species are abundant in fresh waters in Europe and elsewhere, in Portugal anthropogenic pressures on water resources have resulted in many species becoming rare. Consequently, 10 of the 16 native Cyprinidae species have been included in the Portuguese Red Data Book (SNPRCN 1991). Two of the more common cyprinid species, Iberian roach, Rutilus alburnoides (Steindachner), and Leuciscus pyrenaicus Gu ¨nther, are endemic to the Iberian Peninsula and occur in almost all Portuguese (Collares-Pereira 1985) and Spanish (Doadrio 1988) catchments. However, little is known about the ecology of these species (Magalha ˜es 1993a; Ferna ´ndez-Delgado & Herrera 1994; Collares-Pereira, Magalha ˜es, Geraldes & Coelho 1995), their feeding habits (Rodriguez-Jime ´nez 1987; Encina & Granado-Lorencio 1991; Magalha ˜es 1993a,b) or interaction between species. Such information is considered important if a rational strategy for the conservation of these, and other species in the region Correspondence: Prof. M.M. Coelho, Departamento de Zoologia e Antropologia, Faculdade de Ciencias de Lisboa, Bloco C-2, 3° Piso, Campo Grande, 1700 Lisboa, Portugal. e-mail: 2mannela@cc.fc.ul.pt. © 1997 Blackwell Science Ltd 83