Twelve juvenile pink shrimp.Penaeus duorarum Burkenroad, were tested individually for 3-day periods in electronic shuttle-boxes (Ichthyotrons) to determine their thermoregulatory capabilities (temperature preference and avoidance behavior). The shrimp thermoregulated more precisely at night, which was their active period (they were more than twice as active at night as they were by day). Their nocturnal mean thermal preferendum was 29.9 ± 0.2°C (mode 31°C, median 30°C, midpoint 29°C, range of voluntarily occupied temperatures 22–36°C, skewness −0.37). By day they were less active and exhibited much less thermoregulatory precision, spanning a 17–38°C range of voluntarily occupied temperatures out of a potentially available range of 0–50°C (diurnal mean 30.6 ± 0.3°C, mode 34°C, median 32°C, midpoint 27.5°C, skewness −0.76). The range of occupied temperatures was half again as great (21°C) by day as at night (14°C). The 24-hr mean (combined day and night) was 30.3 ±0.2°C (mode 31°C, median 30°C, midpoint 27.5°C, range 17–38°C, skewness −0.18).