Abstract Because dams block migratory routes of potamodromous fish to their spawning areas, and energy generation changes natural flow seasonality, it is necessary to identify spawning areas and their conditions. This information will help in management decisions in the Magdalena River basin regarding the future hydropower development. We identified which characteristics of the tributaries to the Magdalena River are important for determining potamodromous fish spawning grounds, and we estimated the percentage of future loss of spawning areas because of dam development. Ichthyoplankton density is directly related to the floodplain area, and inversely related with channel slope. Low channel slopes offer adult fish a longer distance for their upstream migration and a longer time for embryo development during their drift downstream from the spawning areas to nursery habitats (floodplain lakes). These features could increase the migration distance of the adults, the time for initial embryo development, and, because of its relationship with nursery habitats access, the offspring survival. The potential loss of the actual spawning grounds in the river network was estimated to be nearly 70% because of new dams. Our findings will help to reduce conflicts between hydropower and ecological interests.

Resumen La construcción de hidroeléctricas puede afectar la reproducción de los peces migratorios potamódromos, ya sea porque las represas bloquean las rutas migratorias a sus áreas de desove, o porque la generación de energía cambia la estacionalidad del flujo natural. Esto hace necesario generar información sobre las áreas de desove y sus características, que permitan tomar decisiones de manejo, teniendo en cuenta el desarrollo hidroeléctrico propuesto a futuro en la cuenca del río Magdalena. Identificamos qué características de algunos afluentes del río Magdalena son importantes para los desoves y estimamos el porcentaje de pérdida futura de áreas de desoves debido al desarrollo hidroeléctrico. La densidad del ictioplancton se relacionó directamente con el área de la llanura aluvial e inversamente con la pendiente del canal. Estas características aumentan la distancia de migración de los adultos maduros, el tiempo para el desarrollo inicial del embrión y la supervivencia de la descendencia debido a la proximidad y/o conectividad con los hábitats de cría. La pérdida potencial de las zonas de desove en la red fluvial se estimó en casi el 70% debido a las nuevas presas. Nuestros hallazgos ayudarán a tomar decisiones sostenibles para reducir los conflictos entre intereses de desarrollo hidroeléctrico y ecológicos.

ABSTRACT Tilapia is the most economically important fish in the aquaculture of different countries from the Americas. This species exhibits morphological plasticity under different conditions. In this study, we used landmark-based geometric morphometric to describe the shape variation of two red and one Nile tilapia farmed populations in Colombian Andes. We recorded significant morphological differences between all studied farms (P < 0.001, in the multivariate analysis of variance). In this way, individuals from the Nile tilapia farms were more elongated and had a more ventral position of the posterior extreme of the orbit and the insertion of pectoral fin than red tilapias. Moreover, the Nile group showed a shorter space between the mouth profile and the posterior extreme of the orbit, compared to red groups. On the other hand, individuals from farm red 2 were deep bodied and had a smaller head compared to tilapias from farm red 1. Our results provide evidence that tilapias from different farms in Colombian Andes display differences in body shape, and can be applied to selective breeding programs after establishing the contribution of genetic and environmental effects on tilapia shape as well as the preferences of consumers for the body shape of the species.