The rate of acclimation and temperature tolerance of juvenile yellowtail snappers, Ocyurus chrysurus (Bloch) was tested using the method of sudden exposure to elevated temperature. Acclimations of up to 10 days at various temperatures did not significantly change the 24-hour
lethal temperature from that of a 1-day acclimation. Upper thermal tolerance was tested after 3-day acclimations at 20, 24, 28, 30, and 32°C. Lethal temperatures (for a 7-day exposure) ranged from 32.6°C at a 20°C acclimation to 33.5°C at a 32°C acclimation. No significant
relationship was found between acclimation temperature and lethal temperature. The ultimate lethal temperature was estimated to fall between 33.5 and 34°C. Acclimation significantly raised median resistance times at test temperatures of 34 and 35°C. An upper thermal tolerance polygon
of 108.8 units was constructed by arbitrarily considering 18°C as the lower temperature limit for juvenile yellowtail snappers. Preferred temperature was tested by acclimating and then exposing fish to a horizontal temperature gradient. Acclimation altered the mean preferred temperature,
but the preferred temperature remained within the range normally encountered (24-30°C) by O. chrysurus.
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