Alterations in the <em>Pterodoras granulosus</em> (Valenciennes, 1833) (Osteichthyes, Doradidae) diet due to the abundance variation of a bivalve invader species in the Itaipu Reservoir, Brazil

Abstract

Variations in the diet of Pterodoras granulosus (Osteichthyes, Doradidae) were evaluated from 1994 to 1998 taking into account two events that affected the abundance of an introduced bivalve Corbicula fluminae: (i) the abundance explosion of the bivalve in the reservoir, started in 1994 and (ii) the slaughter of the bivalve population due to fluctuations in water level, started in July 1996. Stomach contents were analyzed and results were shown considering the methods of frequency of occurrence and volumetric, combined in an alimentary index (AI). In 1994, 1995 and 1996 C. fluminae was the most consumed item, constituting about 90% of the diet. A decrease of this item intake (39%) was verified in 1997, with an increase of the vascular plants intake (26%). The diet of P. granulosus changed drastically in 1998, when it became based on algae (49%) and vascular plants (45). These results indicate the important role played by water level fluctuations in reservoirs, on the food availability for P. granulosus