O peixe rei Odontesthes bonariensis é um peixe de água doce de grande importância na região central da Argentina. O objetivo deste trabalho foi descrever a sazonalidade do parasitismo de O. bonariensis no reservatrio La Viña (31º 17'S, 65º 01'W), província de Córdoba, Argentina. Durante os anos 1999 e 2002 foram capturados 573 peixes. Nestes se fez à avaliação da condição corporal usando como parâmetro o peso relativo e identificaram-se os seguintes parasitos: Lernaea cyprinacea (Crustacea), Contracaecum spp. (Nematoda) e Cangatiella macdonaghi (Cestoda). As prevalências e intensidades de Contracaecum spp. foram muito baixas. Houve diferenças nas prevalências de L. cyprinacea e C. macdonaghi na época do ano (P < 0,01), sendo maiores no verão e na primavera, respectivamente. Houve diferenças estacionais na intensidade de L. cyprinacea (P < 0,05) e na densidade de C. macdonaghi (P < 0,01), neste ultimo alcançou-se um valor máximo nas amostras de 32,0 (±22,5) parasitos por cm³ de conteúdo digestivo. Não houve associação entre o parasitismo e o peso relativo dos peixes. Embora haja certa sazonalidade, as diferentes cargas parasitárias encontradas nâo prejudicam a saúde de O. bonariensis enquanto sua condição corporal.

The pejerrey Odontesthes bonariensis is the most important freshwater fish of Argentina central region. The present study was conducted to describe the seasonal variation of parasitism in O. bonariensis from La Viña reservoir (31º 17'S, 65º 01'W), located in the province of Córdoba, Argentina. Between years 1999 and 2002, 573 fishes were caught, and their parasite infection and relative weight (Wr) were assesed. Three parasites were found, Lernaea cyprinacea (Crustacea), Contracaecum spp. larvae (Nematoda) and Cangatiella macdonaghi (Cestoda). Overall, Contracaecum spp. prevalence and intensity were very low. Lernaea cyprinacea and Cangatiella macdonaghi prevalences increased during summer and spring (P < 0.01), respectively. Lernaea cyprinacea infection showed also seasonal differences in intensity (P < 0.05), as well as C. macdonaghi regarding parasites density (P < 0.01). Cangatiella macdonaghi average parasites density was 32.0 (±22.5) cestodes per cm³ of digestive content. No association between parasitism and fish relative weight was found. Besides the seasonality variations observed, the parasite burden found did not compromise fish body condition.

The silverside Odontesthes bonariensis is the most important species in the fisheries of central Argentina. Cap¬ture per unit effort (CPUE), body condition, growth and feeding were studied for O. bonariensis in the Pampean shallow lake "Los Charos" (34º28´S, 64º23´W, 240 ha), located in Córdoba province. Four seasonal sampling procedures were carried out during 2002-2003. Floating gillnets and trawlnets were used to capture the fishes. Specimens captured (n= 2862) were ranged between 38 and 380 mm of standar length (StL). CPUE average was 74.3(±71,0) kg/20 hs/gillnets. The StL-weight relationship showed signifficant differences along the sea¬sons (P< 0,01). The body score indices were within the reffered limits for this species. Growth was calculated by StL(t)= 459,8*[1-exp(-0,3105*(t-0,175))]. The StL-Total length (TL) ratio was TL(mm)= 8,23+StL*1,14 (n= 283; R2= 0,99). For the young fishes the zooplankton constituted a secundary feeding source. In individuals older than 3 years of age, a marked canibalism was observed, which might explain partially their body condition. The shallow lake "Los Charos" shows an elevated production of O. bonariensis.

El pejerrey Odontesthes bonariensis es la especie más importante de las pesquerías del centro de Argentina. Se estudio la captura por unidad de esfuerzo (CPUE), la condición corporal, el crecimiento y la alimentación de O. bonariensis de la laguna pampeana Los Charos (34º28´S, 64º23´W, 240 ha), ubicada en la provincia de Córdoba. Se realizaron cuatro muestreos estacionales en el periodo 2002-2003. Para la captura de peces se utilizaron redes de arrastre y enmalle. Se capturaron 2862 ejemplares de un rango de talla comprendido entre 38 y 380 mm de longitud estándar (LSt). La CPUE promedio fue de 74,3(±71,0)kg/20 hs de tendido de red. La relación LSt-peso presentó diferencias significativas entre épocas del año (P< 0,01). Los índices de condición corporal estuvieron dentro de los límites de referencia de la especie. El crecimiento calculado fue: LSt(t)=459,8*[1-exp(-0,3105*(t-0,175))]. La relación LSt-Longitud total (LT) fue: LT(mm)=8,23+LSt*1,14 (n=283; R2=0,99). El zooplancton constituyó un ítem alimenticio secundario en los peces jóvenes. En los ejemplares de 3+ años de vida se observó un marcado canibalismo, situación que explicaría en parte su mejor condición corporal. La laguna Los Charos presenta una elevada producción de O. bonariensis.