CUMULATIVE PATTERN IN PH CHANGE ALTERS RESPONSE TO FOOD IN THE CRAYFISH CAMBARUS-BARTONI

In the relatively acid-tolerant crayfish Cambarus bartoni, locomotory response to food was tested (as delay in response, or latency) at both a circumneutral and a sublethal acid pH. Crayfish moved through a Y-m aze toward a food source. Sequential tests were at pH 7.5, 4.5, and 7. 5, and then again at pH 4.5 and 7.5. One group of 21 crayfish experien ced a series of smaller pH shifts (7.5 to 6.5 to 5.5 to 4.5 at 5-day i ntervals), immediately followed by a larger pH shift (7.5 to 4.5). A s econd group of 20 crayfish experienced the large shift first, and then the series of smaller shifts. Both groups showed gradually decreasing latency through the first cycle, but then a large latency increase wi th the second shift to pH 4.5 (P < 0.005 and P < 0.03), and subsequent recovery at pH 7.5 by the first group (P < 0.006) but not the second (P < 0.32). This effect would seem to be due to the previous pH shift, which apparently exceeded their tolerance within our 45-day testing p eriod. An initial tendency to approach the food (P < 0.01 and P < 0.12 ) became food avoidance (P < 0.01) and (or) no preference during eithe r the first or second exposure to acidic pH.