A model power plant, constructed to simulate the time-temperature exposure histories experienced by organisms entrained in the intake of an actual plant, was used to study the thermal effects of an operating power plant on the hatching success of American shad, Alosa sapidissima, eggs. Eggs from a single female were divided into 5 sub-samples; two controls, and three experimental batches. One control was stocked immediately in a constant temperature bath. The second control was passed through the unheated plant to assess the mechanical effects of passage through the model plant on hatching success. The experimental batches of eggs were passed through the operating plant set to produce a Δ T of about 6°C, and were cooled at different rates to the intake temperature of 18.5° C. Exposure times to a Δ T of at least 6° C ranged from 5 to approximately 15 minutes, and the cooling period from I hour to nearly 3 hours. The hatching success of each of the controls was 88%, and it ranged from 82% to 84% for the experimental batches, being highest for the sub-sample with the shortest exposure to elevated temperature. The differences in the hatching success of the controls, and the experimental batches were however, not statistically significant.
