Tools of histochemistry and digital image analysis were used to quantify changes in the coverage area of lipid droplets (lipid content) of oocytes of the penshell Atrina maura during oogenesis and to determine its relation to changes in water temperature and seston content. These data led to calculating a lipid index as a criterion of gamete development and quality. Gonads were collected monthly for 18 mo and prepared for histochcmical processing with Sudan Black B for identification of lipids. Finished slides were digitized for determining stages of oogenesis and variations in the size of oocytes. Two periods of greatest reproductive activity occurred during the study, with a lower peak from November through January (∼15°C; 26 mg/g) and a major peak from April through June (∼20°C; 25–40 mg/g). Oocyte area significantly varied during the stages of active development (516–2,743 µm²), ripeness (1,073–2,930 µm²), spawning (145–2,939 µm²), and atresia (331–2,001 µm²). Lipid incorporation into oocyte cytoplasm followed a clear seasonal pattern, peaking again in winter and spring. Temporal variations in the lipid index and its relation to oocyte diameter were irregular, but also peaked in winter and spring. Histochemistry and digital image analysis resulted in reliable methods for estimating oocyte development and quality in this species, and can certainly be applied in studies of reproduction of other bivalve, invertebrate, and vertebrate species.