Use of erythrocyte measurements to identify triploid saugeyes

The use of erythrocyte size measurements as a possible alternative to flow cytometry for identifying triploid saugeyes (female walleye Stizostedion vit-reum X male sauger S. canadense) was evaluated. Blood smear preparations were made from 32 heat-shocked saugeyes (1.0-42.7 g; 52-185 mm total length), which consisted of 12 diploids and 20 triploids, as determined by flow cytometry after blood cells were stained with propidium iodide. The length, width, surface area, and volume of the cell and nucleus of 100 erythrocytes were determined for each fish. The cell and nuclear dimensions were measured at 1,000X magnification with a calibrated ocular micrometer. Discriminant analysis was used to distinguish diploids and triploids based on their score profiles. Results showed that triploid saugeyes had significantly larger erythrocyte cell and nucleus measurements than their diploid counterparts (N = 32; P < 0.0001). Erythrocyte measurements correctly distinguished 93.8% of fish samples as diploids or triploids, but measurements require about 1 h/fish. The potential applications of this technique for fisheries management and aquaculture are discussed.