Tolerance of Mysis relicta to Thermal Shock and Light

Abstract
Tests were conducted to determine the thermal tolerance and effects of laboratory illumination on survival of Mysis relicta. Mysids were affected adversely by heat stress when temperatures rose above 10 C. When acclimated to a temperature of 7.5 C, this species had 96‐hour median tolerance limits of 16 to 16.5 C. Percent mortality was essentially the same when the animals were subjected immediately to test temperatures, as when temperatures were raised gradually from acclimation temperature over a period of 5 hours. When acclimated to a temperature of 4.5 C and then subjected to temperature elevations of 1 ° 2.5 °, and 5 ° C per day, 50% of the animals died at 16 C in 16 days, 18 C in 6 days and 16 C in 4 days, respectively. It is suggested that Mysis relicta is an organism requiring considerable time for effective acclimation. Mysids were intolerant of exposure to normal laboratory illumination. The species lived satisfactorily in light of 10 hours a day for 2 weeks, but this period was followed by a steady mortality of about 8% of the original population per week.

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