Effects of temperature and salinity on thermal death in postlarval brown shrimp, Penaeus aztecus.
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Postlarval brown shrimp acclimated at three temperatures (24.0, 29.0, and 34.0 C) were exposed to nine lethal temperatures for each acclimation temperature (36.0-37.6 C, 38.0-39.6 C, 38.6-40.2 C). Postlarval brown shrimp acclimated at the nine possible combinations of three acclimation temperatures (24.0, 29.0 , and 34.0 C) and three acclimation salinities (%5, 15%, and 25%) were tested for thermal resistance time at three test salinities ( 5%, 15%, and 25%) for each of two lethal high temperatures. Resistance time increased with increasing acclimation temperatures and decreased with increasing lethal temperature. Longer resistance times occurred at the higher test salinity (25%) than at the other two salinities. The lower acclimation salinity (5%) proved to be a better preparation for resisting lethally high temperatures, at all three test salinities, than either of the other two acclimation salinities. These results provide evidence of a new relationship between environmental salinity and the temperature tolerance of an estuarine organism. A reduction in the amount of work necessary for osmoregulation at 25% as compared with the two lower test salinities is thought to explain the higher thermal resistance at higher test salinities. Improved thermal resistance at all test salinities after acclimation at 5% is considered to be an adaption allowing the postlarvae to resist high temperatures when they are in low-salinity bays.