Laboratory Mass Culture of the Freshwater Oligochaete Dero digitata

Proliferative gill disease (PGD) in channel catfish Ictalurus punctatus 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 D. digitata mass cultures. We developed methods to grow and sustain large D. digitata populations and compared population growth in aerated versus nonaerated containers. White paper towels (2–3‐cm squares) were placed into six 10.7‐L dish pans into which 4 L of autoclaved pond water from commercial channel catfish ponds were then added along with 0.1 g of fish food. Each of the six dish pans was 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 once each week for 5 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. Over 5 weeks, the mean number of worms per pan increased significantly more in the nonaerated pans than in the aerated pans. 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 3,000–6,000 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. Received March 12, 2010; accepted May 24, 2010