Seasonal changes in oocyte development, growth and population size distribution of Percilia gillissiand Trichomycterus areolatus in the Itata basin, 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.