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Monthly plankton collection of eggs and larvae of sea bream Archosargus rhomboidalis were made in Terminos Lagoon, Mexico, from February 1980 until April 1981 in order to determine the species' spawning season and area and adult stock size, and to study aspects of its early life history. Spawning occurred from January to July, and was most intense from January to April, when temperature ranged from 21.5 to 29.9 C and salinity from 8 to 38% Major spawning areas were above sea grass beds. The estimate of annual egg production was 8 × 1011. Adult females were considered to be multiple spawners during one spawning season. Fecundity was related to fish length and weight and the relative fecundity was 485 oocytes per gram body weight. The egg production divided by relative fecundity and adjusted for a proportion of 60% females among adult fish gave an estimate of 2,700 metric tons for adult biomass. Larvae are carnivorous, feeding mainly on copepods, and prey size showed a clear relationship to mouth diameter and digestive-tract length of larvae. Larva growth was studied from daily growth increments on otoliths and mortality rate was estimated in relation to larva length and age. Mortality was 35% per day during the first 2 weeks of planktonic life, 17% per day until metamorphosis, then 0.2% per day until age 1 year.