Growth, size composition, condition factor and gonad index of the oil sardine,Sardinella longicepsVal., oscillated over an annual cycle in relation to upwelling. Growth in length was modelled using the formula of Pauly&Gaschütz (1979):whereLt= length cm at agetyears, L∞= 23.8cm, K=0.97, to=0.70, C=1.08 and ts=−0.08. The relationship of growth rate, spawning, and condition factor, to upwelling and plankton blooms is discu