Seasonal changes in oocyte development, growth and population size distribution of Percilia gillissiand Trichomycterus areolatus in the Itata basin, Chile Cambio estacionales en el desarrollo de oocitos, crecimiento y distribución de talla poblacional de Percilia gillissi y Trichomycterus areolatus en la cuenca del río Itata, Chile

There is scarce basic biological data on native freshwater fish species from Chile and next to zero on growth, gonad development and reproduction, which are critical for the purposes of the conservation of their natural populations. Seasonal analysis of sub-individual (oocyte development) and population (length frequency, growth rates) endpoints in Trichomycterus areolatus and Percilia gillissi were evaluated from February 2007 to January 2008. Oocyte development has a marked seasonality for P. gillissi, with mature eggs in October and declining frequency of mature oocytes into January. For T. areolatus we found some mature eggs in July, with highest number of mature eggs in October, coincident with previous data on maximum gonad size. Both species showed a multiple spawning reproductive strategy, with a long spawning season starting in spring to early summer. Increased numbers of juveniles were observed during mid-summer for P. gillissi,and during the end of the summer and beginning of autumn for T. areolatus. Juveniles had a higher growth coefficient (K) (0.56-0.38 mm month-1) than adults (0.29-0.15 mm month-1), and almost all juveniles in the population reached maturity before the spring (>50 mm for T areolatus and >40 mm for P. gillissi) and were incorporated into the population as a new recruitment cohort. Knowledge of the seasonal variability of these individual and population level responses can help better understand the biology of the species, and simultaneously improve the management and conservation of freshwater biota in Chile. Existen escasos datos de biología básica sobre las especies de peces nativas chilenas de agua dulce y casi ninguno en sobre el crecimiento, el desarrollo gonadal y reproducción, que son fundamentales para los propósitos de la conservación de sus poblaciones naturales. El análisis estacional de los parámetros sub-individuales (desarrollo de oocitos) y poblacionales (frecuencia de tallas y tasa de crecimiento) en Trichomycterus areolatus y Percilia gillissi fueron evaluados entre febrero de 2007 y enero de 2008.El desarrollo de los oocitos posee una marcada estacionalidad en P. gillissi con oocitos maduros en octubre y una disminución de estos estados maduros hacia enero. En T. areolatus encontramos oocitos maduros en Julio, pero con una mayor abundancia durante octubre, coincidente con datos previos de máximo desarrollo de la gónada. Ambas especies mostraron una estrategia reproductiva de desoves multiples, con una temporada de desove que comienza en primavera hasta principios de verano. Ambas especies evidencian un ma