Origin of Chironomid Larvae in Plastic-Lined Culture Ponds: Airborne or Water Supply?

Abstract

Twelve 0.26-m³, shallow, plastic pools at an Iowa fish culture facility were used as mesocosms to determine the mode (airborne versus water supply) and rate of colonization by benthic chironomid larvae without the predation pressure of fingerling walleyes Sander vitreus. Chironomid larvae have particular importance in the culture of walleye fingerlings. Concurrent with walleye hatchery operations in nearby plastic-lined production ponds, pools were filled and then fertilized using the same protocols as the production ponds. A 2 × 2 factorial experimental design was used that included screened (1,000-μm mesh over the top of the pools) and nonscreened pools and filtered (75-μm-mesh sock) and nonfiltered water in the pools. Chironomid larvae were sampled twice during the 5-week culture season with Hester–Dendy samplers. At the end of the walleye culture season, there were no significant differences in chironomid density between filtered (108 larvae/m²) and nonfiltered (657 larvae/m²) pools, but nonscreened pools (592 larvae/m²) had larger densities of chironomid larvae than screened pools (174 larvae/m²). These results suggest that airborne movement and egg deposition by chironomid adults, rather than transfer of organisms from the water supply reservoir to the culture facility, constitute the primary method of chironomid colonization in plastic-lined ponds.