This study was carried out with a natural population of the brine shrimp Artemia from Bahía Salinas, in Carmen Island, Baja California Sur, México, with the purpose to determine different ecological and biological characteristics of this crustacean. The field work was performed in two periods in 1999: March to June and August to September. In both periods, the variation of temperature, pH, salinity and depth of 13 saline ponds was monitored. Brine shrimp were present in ponds with salinity between 115 and 195 g l-1. Minimum and maximum values of water temperature were 15 and 35 °C. The pH ranged from 7 to 8. The average diameter of hydrated cysts and size of newly hatched nauplii was 201.3 μm ( ± 12.8) and 473.5 μm (± 73.9), respectively. The morphometric analysis of adults showed significant differences between sexes. The population density fluctuated from 6 to 55 specimens per liter. The monthly male:female ratio was dominated by the females. Females displayed different offspring output, with ovoviviparity being dominant over oviparity. The individual fecundity oscillated between 10 and 87 cysts. The effect of water temperature and salinity on biological parameters of the adults is discussed.