Changes in oviduct structure in the black tiger shrimp, Penaeus monodon, during ovarian maturation

To examine the structure of the oviduct of the shrimp Penaeus monodon. The oviducts of P. monodon with three different major groups of ovarian development (Group (Gr.) 1: Stages I & V; Gr. 2: Stages II & III; and Gr. 3: Stage IV) were examined by light, transmission electron, and scanning electron microscopies, respectively. The epithelium of the oviduct in Gr. 1 was composed of tall simple columnar cells with their basal nuclei located on the basement membrane and its thick collagen fibers. In Gr. 2, the oviduct seemed to produce some substances and their epithelial cells became transitional with centrally located nuclei and formed some vacuoles. Obviously, the epithelial cells in Gr. 3 (at Stage IV) were disorganized, disrupted, and shed accumulated spherical secretory substances including some cellular contents into the lumen. The structural changes of the P. monodon oviduct were related to ovarian maturation stages (Grs. 1-3). Prior to spawning, only the oviduct epithelium at ovary Stage IV produced and secreted a number of spherical secretion substances into the lumen. These substances may act as the oviductal lubricants to facilitate the spawning process.