Presently, there are no immortalized Daphnia cell lines. Our current efforts include the development of primary cell lines derived from Daphnia tissue. Cell lines will provide a controlled environment for basic biological studies and transformation (reverse genetics) studies in Daphnia. Cell lines are being derived from embryos and ovarian tissue. To avoid bacterial and/or fungal contamination, adult females are first surface sterilized prior to removal of the embryos and ovaries. The embryos are then subjected to a second round of surface sterilization prior to dissection. Various insect media formulations with supplements are used to determine optimal growth conditions keeping in mind the osmolarity and pH of Daphnia tissues. In general, cultures derived from primary tissues may require a year or more of continuous care before establishing a continuously growing population of cells.