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602 BULKLEY AND PIMENTEL the disease were not tested during disease treat- ment or for 21 days thereafter . We do not believe, therefore, that disease altered re- sponses to temperature. The flow-through tanks were supplied with dechlorinated water. Dis- solved oxygen was maintained in the tanks at 90-100% saturation; ammonia was below 0.2 mg/liter and pH was about 8.0. Temperature preference and avoidance were determined with an electronic shuttlebox de- signed by Neill et al. (1972) and adapted by McCauley et al. (1977) to use heated and chilled inflowing water instead of submerged heaters. This device was a 45-liter plexiglass chamber of two compartments connected by a narrow pas- sageway. Temperature differences in the two chambers did not exceed 1 C under test con- ditions. Individual fish were able to regulate water temperature by triggering photocells controlling flows of warm and cold water at the rate of 0.7 -0.8 liter/minute. Fish movement in one direction triggered flow of warm water into the compartment entered and turned off cold water in the compartment left; movement in the opposite direction turned off the warm water, and turned on cold water when the "cold" compartment was entered. The apparatus was capable of providing a range of temperature from 4 to 41 C in the shuttlebox; maximum rate of change was 0.2 C/minute. Water tem- perature was monitored by a continuously re- cording Honeywell Model 602C 1 D-34-7 5 ther- mograph with a precision of :t 1 C. Photoperiod was the same as in acclimation tanks and was maintained by an overhead 60-watt light bulb. Fish were placed in the shuttle box that had been filled with water from their acclimation tank (same temperature); the photocells had been deactivated. After the fish had habituated to the apparatus for 1 hour, the photocells were ac- tivated, allowing either warm or cold water to enter the shuttlebox, depending on which side the fish was in at the time of activation, After 48 hours of testing the fish was removed, re- turned to the holding tank, and observed for another 24 hours. Fish that died during the 48- hour test or recovery period were excluded from analysis of temperature preference and avoid- ance. At least 19 fish from each acclimation temperature were tested in the shuttlebox. The initial 24-hour period was used to esti- mate temperatures avoided by each fish because most fish exposed themselves to the highest and lowest temperatures experienced during the whole test period shortly after they were placed in the shuttlebox. Activity appeared to be di- rected toward avoidance of undesirable tem- peratures when fish first were placed in the shut- tlebox. Later, as length of time in the apparatus increased, the activity was directed into an in- creasingly narrow temperature range as the fi- nal preferendum was sought out. Hence, we examined data collected during this orientation period to estimate upper and lower avoidance temperatures, and to compare ability among groups to gravitate toward a final preferendum. A voidance temperature has been measured di- rectly by providing fish a choice of water warm- er or cooler than that to which they have been acclimated (for example, Meldrim and Gift 1971; Cherry et al. 1975). When a fish demonstrates active avoidance, that temperature is assumed to be the avoidance temperature. In a sense, the shuttlebox provides a similar situation during the first few hours a fish is in the box. When a fish experiences a high temperature that is pre- sumably unsatisfactory, for example, it moves away from the flow of warm water and triggers the photocells, thereby provoking an immedi- ate decrease of 0.2 C/minute in water temper- ature within the chamber. The reverse occurs when an individual finds itself in water presum- ably colder than desired. It is possible that in-. dividual fish in our tests might not have re- sponded immediately when temperature reached a point that would normally elicit an avoidance response, but the same behavior could occur in the two-choice apparatus also, Neill and Magnuson (1974) used the elec- tronic shuttlebox to estimate avoidance in terms of median upper and lower turnaround tem- peratures, temperatures at either side of the box that, when reached, were abandoned by thermoregulating fish. Our method, based on the extreme temperatures experienced by fish during their first 24 hours in the shuttlebox, is not analogous to theirs and probably provides a wider range of acceptable temperatures. We prefer our method as a basis of design criteria for new water-control structures but the rela- tionship between our method and others used to estimate avoidance temperature needs to be investigated. Upper and lower avoidance temperatures for each acclimation group were the mean highest or lowest temperatures experienced by individ- ~ .. . I