Two Counting Cells for the Enumeration of Zooplankton Micro-Crustacea

tained more than 400 eggs. In the absence of aeration only 11 of 40 bowls had hatches of nauplii, even though the bowls were uncovered and the water was shallow. With gentle aeration for 12 of each 24 hours, 28-33 bowls contained at least one nauplius after each rehydration. Of the hatches, only 4-7% of the nauplii counted in each hatch matured to the egg-bearing stage, if no food supplement was added. With the addition of 5 ml of filtered pool water containing bacteria grown on boiled egg-yolk (Brandwein, 1937) and 0.5 g of Coffee-mate (a commercial cream-substitute) added to each bowl once each 48 hours, 7-10% of the nauplii developed into ovigerous females. With the addition of either Coffee-mate or bacteria-containing water alone, a maximum of 7% of the nauplii matured into ovigerous females.