Age, growth, length-weight relationship, sex ratio and food habits of the Argentine pejerrey, Basilichthys bonariensis (Cuv. and Val.), from Lake Peiiuelas, Valparaiso, ChileArgentine pejerreys were collected in Lake Pefiuelas during January 1973. Calculated growth rate was maximum during the 3rd year of life. The length-weight relationship was:log W=-5.69395+3.25248 log L, where W=weight (g), and L=total length (rnm). Agegroup I was sexually mature. The sex ratio was 85 males (54%) to 73 females (46%). Young-of-the-year pejerreys fed primarily on copepods, but cladocerans [Bosmina sp. (Baird), Diaphanosonza brachyurum (Likven), Simocephalus serrulatus (Koch)], ostracods, and dipterans were also represented. Feeding occurred during daylight. w x 105 K = -299 L3