Technical Abstract: Proliferative gill disease (PGD) in channel catfish is caused by the myxozoan parasite Henneguya ictaluri, which uses the freshwater oligochaete, Dero digitata, as an alternate host. Controlled studies on the transmission of PGD require sustainable Dero digitata mass-cultures. Here we describe methods to grow and sustain large D. digitata populations while comparing population growth in aerated versus non-aerated containers. White paper towels (2-3 cm squares) were placed into 10.7-L dishpans. Four liters of autoclaved pond water from commercial catfish ponds was then added to each dishpan with 0.1 g of fish food. Each of six dishpans were initially stocked with 100 D. digitata and maintained at 22-25'C; three pans received aeration and three did not. All worms were counted and returned to their respective pans weekly for five weeks. To compensate for evaporative loss, autoclaved pond water was added to the pans weekly, and pond water and paper towels were completely changed after 4 weeks. The mean number of worms/pan increased significantly more in the non-aerated treatments when compared to the aerated treatments over five weeks. We have maintained D. digitata mass cultures in our laboratory for over a year, starting with two pans containing 100 worms each. Through routine exchanges of pond water and paper towel squares, these populations have expanded to 16 pans, each supporting from 3,000 to 6,000 worms. We have also removed thousands of worms periodically to give to other researchers or for research in our laboratory. Using methods described here, researchers can maintain D. digitata mass cultures and predict population numbers that will be available at given times for studies on myxozoan life cycles and oligochaete control.