Improvements in closed-system culturing methods for marine invertebrates are important prerequisites for the generalized use of transgenic lines. We discuss here the effects of several closed-system conditions on the growth and survival of the solitary ascidian, Ciona intestinalis. In Shimoda, close to the sea, a small-tank system was used to ensure that tanks and systems were reasonably equipped, water exchange was rapid, and animals separated to minimize the risk of infection. In Gif-sur-Yvette, an inland site, we tried to determine the optimal conditions to limit handling operations, and to save artificial seawater by avoiding water pollution. A mixture of at least two types of live algae was better than any single-organism diet. With these maintenance protocols, we were able to obtain several generations of Ciona intestinalis, including several transgenic lines. Because these systems make it easier to rear Ciona intestinalis in laboratories, they increase the potentialities of this model organism for research. Developmental Dynamics 236:1832–1840, 2007. © 2007 Wiley-Liss, Inc.