Abstract: A system and apparatus for the growth of hydrozoa, e.g. hydra is disclosed which comprises a tank having a fluid medium therein for the growth of the hydra and pump means for recycling and filtering the medium. Temperature control and oxygenation apparatus may also be provided. In a preferred embodiment, the tank has a roughened surface for the attachment of hydra thereto so as to form a stable resident population of hydra. When it is desired to remove a quantity of hydra for an experiment, they can be dislodged from the surface by means of, e.g., a razor blade and collected, by means of the recycle current, on a net disposed in the current path.