The bocachico, Prochilodus nigricans, is a commercially important fish distributed throughout the central and western Amazon. Age and growth of this species in eastern Ecuador were determined by otolith and scale increment analyses. For otolith analyses, we used thin sections of the astericus, and clear visualization of annuli required the use transmitted polarized light. Accuracy and precision of age estimation were compared to select the best ageing structure. Precision indices showed that otoliths are more reliable than scales to determine the age of bocachicos. Based on marginal increments analysis, we found that annulus formation in both structures occurs once a year between August and December. Seasonal changes in growth were associated with hydrological cycle of the river. The Ecuadorian Prochilodus at the juvenile-adult stage grew faster (i.e., K = 0.29 for ages 2 and older) than conspecific populations from Bolivia and Brazil (K = 0.5). In addition, annual mortality rate (A = 0. 56) was lower than reported for Prochilodus populations elsewhere in the Amazon. We conclude that this population is presently not overexploited, but conservation and management schemes for this population will need to consider that it is an international, trans-boundary migrant.

The black prochilodus, Prochilodus nigricans, is an important food fish distributed throughout aquatic habitats of the Ecuadorian Amazon. We sampled gonad weight, body condition, and feeding of this species to address the question of whether changes in these biological parameters are related to hydrological variation and migration patterns. High frequency of empty stomachs and poor body condition corresponded to migration periods. Gonad condition analysis revealed a single, discrete spawning period in April (end of rising water season). We synthesized our own and published observations on migration patterns of black prochilodus and presumptive factors that influence those movements. Mature individuals make lateral migrations from peripheral flooded habitats to large white water rivers to spawn. Eggs and larvae drift downstream to nurseries at least into Peru and perhaps into Brazil; there do not appear to be nursery habitats in Ecuador. After 6-18 months, they migrate upstream, recruiting to parental stocks. Long-distance migrations of black prochilodus and similar fishes in Neotropical rivers disobey political boundaries. Conservation and management of such migratory fishes, thus, requires international co-operation and integrated conservation efforts.Keywords: Black prochilodus, Condition factor, Gonadalsomatic index, Life-history, Stomach fullness.El bocachico, Prochilodus nigricans, es una fuente importante de proteínas, distribuido en hábitats acuáticos de las tierras bajas de la Amazonía ecuatoriana. Se muestreo el peso de las gónadas, la condición corporal, y alimentación de esta especie para determinar la relación de estos parámetros biológicos con la variación hidrológica y patrones migratorios. Una frecuencia alta de estómagos vacíos y la pobre condición corporal corresponde a períodos de migración. El análisis del estado de las gónadas reveló un corto periodo de desove en abril (fin de la temporada de aumento del río). Hemos sintetizado nuestras observaciones propias y publicadas sobre migraciones del bocachico, así como los factores que presumiblemente influyen en estos movimientos. Los peces adultos migran lateralmente desde hábitats periféricos inundados hasta ríos de aguas blancas para desovar. Los huevos y larvas flotan aguas abajo hasta llegar a sitios de crianza en Perú y posiblemente en Brasil; no parece haber hábitats de crianza en Ecuador. Después de 6-18 meses, los bocachicos migran aguas arriba, reclutando a las poblaciones parentales. Las migraciones a larga distancia del bocachico y peces similares en ríos Neotropicales desobedecen las fronteras políticas. Una gestión apropiada de este recurso requiere de cooperación internacional y esfuerzos integrados de conservación.Palabras Clave: Bocachico, Factor de condición, Historia natural, Índice gonadosomático, Llenura del estómago.