Fig. 1 is a schematic representation of the present culture system All tanks are constructed of 1 cm thick, solvent-welded acrylic plastic, and tubing is either Pyrex glass, silicone rubber, or nylon. The pump surface in contact with the medium is polypropylene, except for a titanium shaft. Polyethylene and polyvinyl chloride also are used in the system. None of these materials had any demonstrable effect on the copepods when tested separately. The 2 culture tanks have a capacity of 100 l each. Culture medium passes through removable screens into troughs extending the width of the tanks, and flows out through a gravity drain.