Water Management to Control Clam Shrimp,Cyzicus morsie in Walleye,Stizostedion vitreum,Production Ponds

Clam shrimp, Cyzicus morsie , can occur in hatchery ponds in such dense numbers that they interfere with production of fish. Hatchery ponds are frequently left dry during the fall and winter and are filed in spring or early summer, simulating the vernal pools where clam shrimp naturally occur. Ponds left dry over winter and ponds that were full over winter, but were drained and dried for a period of time immediately prior to stocking, had the highest numbers of clam shrimp (P = 0.001). Few or no clam shrimp were collected in ponds that were full over winter and were not dried in the spring. High turbidities were observed in ponds with high numbers of clam shrimp; however, clam shrimp were not the only cause of turbidity. The largest number of walleye were produced in ponds which contained few or no clam shrimp. Clam shrimp were controlled by preventing hatchery pond substrate from drying during winter and early spring; however, the absence of drying may cause other problems that interfere with fish production.