Closed Systems for Long-Term Propagation of the Marine Tunicate Botryllus schlosseri Isolated from Natural Seawater

Advanced methodologies for Botryllus schlosseri artificial seawater systems are needed to decrease dependency of large-scale culture on natural seawater and expand this important new model organism to more inland laboratories. We constructed two botryllid tunicate customized closed aquaculture systems, a static system consisting of aerated jars fed commercial filter feeder diet, and a recirculating aquaculture system (RAS) consisting of pertinent marine RAS components fed live microalgae and zooplankton diets. Initially, static tunicate culture yielded exponential growth in contrast to poor survival and negligible growth observed in RAS tunicates. RAS modifications were made to increase water treatment proficiency, which improved tunicate survival and growth. Experiments were performed isolating feed and water type as variables differentiating static and RAS and evaluating their specific effects. Live feed promoted five-fold greater growth relative to a commercial concentrate diet. Tunicates maintained in optimized RAS water achieved two-fold faster growth relative to animals in freshly prepared artificial seawater. Subsequent procedural modifications combined with the RAS revisions resulted in growth rates comparable to the static system. Both optimized systems are suitable for long-term husbandry of botryllid tunicate populations supporting both sexual and asexual modes of reproduction, with a current RAS residence time of over 24 months.