- Abstract The reproductive readiness of the marine shrimp Litopenaeus vannamei (formerly Penaeus vannamei ) cultured in brackish water was characterized by applying morphological, physiological, and molecular tools. The shrimp were cultured on two commercial shrimp farms in brackish water that was pumped from artesian wells that tap into a geothermal aquifer. The shrimp populations exhibited a bimodal growth curve with the females being significantly bigger than the males at the end of the growout period. Some male shrimp started to develop spermatophores about 6 months after the first post-larval (PL 0 ) stage, and some with developed, normal-looking, white spermatophores were observed 8 months after PL 0 . The sperm count in these males was 10.1×10 6 ±5.8×10 6 cells per compound spermatophore, and 81.6±19.8% of the cells were spiked. Melanization of the males, which eventually affected about a third of the male population, first became evident before the appearance of white spermatophores. Female ovaries were transparent and appeared to be arrested in a previtellogenic stage. However, beyond a weight/age threshold of 20 g/8 months, some of the ovaries had become opaque and the vitellogenin gene was found to be expressed in the ovary—but not in the hepatopancreas—of 7 out of 10 females. A unique case of a 46.8 g female with a fully developed ovary that was found in the brackish-water-held broodstock is reported.