... purposes of comparison) the upper and lower ends of this range are defined by survival of 50% of a sample of individu-als similar in size, health and other factors, for a specified length of time, ... FISH ECOLOGY 1151 24. Parker, F.L. and P.A. Krenkel, 1969b, Thermal pollution: Status of the art, Dept. of Envir. and Water Res. Eng., Vanderbilt Univ. Rept. No. 3. 25. Parker, F.L. and P.A. ... det-rimental to desired fish populations. The key to controlling “thermal pollution” is a firm understanding of how tempera-ture affects fish, and of the circumstances that truly consti-tute...