The monthly variation in the biochemical composition of the digestive gland, the adductor muscle and the gonad and its relationship with the gonadal index (GI) were studied during 2 years in a wild population of Hyotissa hyotis living in the Gulf of California. Protein was the main constituent of the gonad, digestive gland and adductor muscle. Temperature (20°C to 24°C) favored the accumulation of protein in the muscle during gametogenesis. Carbohydrates and lipids were stored in the gonad, digestive gland and adductor muscle during the spring gametogenesis to support the reproduction effort. Three spawning periods were detected, one in the first year and two during the second.