Rosowski, J.R., M.A. Gouthro, K.K. Schmidt, I.A. Messaad, N.A. Brittell, L.J. Young
Abstract:
A common sampling procedure for determining the percent hatch of nauplii from brine shrimp cysts, the Imhoff sediment settling cone apparatus, was compared with a enumerative procedure using small Petri dishes. Each procedure requires about two-three hours total to set up and evaluate, not counting incubation time to hatch. The sampling procedure with Imhoff cones utilized 1g of cysts/1 liter cone, had a percent mean hatch of 65% and a SD of 11. The enumerative procedure utilized a count of 100-180 cysts adhered to a one cm disc of transfer adhesive on the bottom center of each of twenty to thirty 60 mm diameter sterile plastic Petri dishes. Six experiments using the enumerative procedure gave estimates of the mean percent hatch ranging from 84-87%, with a SD range of 3 to 7. Hatchability was underestimated by the cone procedure. From our estimates of the variance in the enumerative procedure, we recommend the use of 30 dishes per treatment when the SDs are high instead of twenty. This gives a power of 87% to detect differences of 5% or greater among treatments at an alpha level of 0.05 for our largest SD. The use of the enumerative procedure by several technicians over the past three years suggests good reproducibility when the water source and other hatch parameters are constant.
(School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0118, USA)
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