Abstract
Laboratory and field experiments were made to examine the effects of time of day, water depth, and roughness of substrata on the egg deposition of Argulus coregoni. Egg-laying occurred normally at night (98%, 93/95) ; however, mature females laid eggs even in the daytime under experimentally dark conditions. The oviposition was thus considered to be influenced by the absence of light.
The relationship between water depth and egg deposition was examined in trout ponds of 65 cm and 140 cm deep by hanging acrylic plates as substrata for the egg deposition, and the clusters of eggs deposited on the plates were analyzed. The clusters were found to be more abundant nearer the bottom of both ponds : 88% of the total number of clusters deposited at a depth of 45-65 cm in the pond of 65 cm depth and 74% at a depth of 100-140 cm in the 140 cm-deep pond.
The parasite showed a preference of roughness of substrata. Only a few egg clusters were deposited on transparent glass (smooth substratum of less than 0.5 μm maximum height of roughness) and on a wooden plate (rough substratum of more than 50 μm), whereas abundant egg clusters were found on frosted glass or unglazed tile with a roughness of about 9 μm.
Methods of control of A. coregoni utilizing these results are also discussed.
