AbstractSeasonal variation in population density, birth rate, mortality and production of a daphnid was studied in a high, altitude sub‐tropical lake. A bimodal growth curve with maxima during summer and autumn was observed. A positive correlation was reported between fecundity and death rate, probably due to a difference in age specific death rate combined with a high relative frequency of juveniles in a growing population. The production ofDaphnia longispinacorrelates better with temperature than with food. TheP/Bratio was higher during summer and autumn month