A comparison of the avoidance responses of individual and schooling juvenile Atlantic menhaden, Brevoortia tyrannus subjected to simultaneous chlorine and delta T conditions.

The objectives of this study were to determine and compare the avoidance responses of individual and groups of Atlantic menhaden, Brevoortia tyrannus, exposed to simultaneous elevated temperature (0, 2, 4, and 6 degrees C) and total residual chlorine (TRC) (0.00, 0.05, 0.10, and 0.15 mg/l) conditions. An unbalanced three-factor factorial design was used to develop predictive avoidance models with this species at a test temperature of 25 degrees C. Fish tested in groups elicited the following avoidance responses: (1) a high avoidance response occurred at 0.10 and 0.15 mg/l TRC regardless of delta T; (2) avoidance increased with increasing delta T values at 0.00 mg/l TRC; and (3) TRC was the most important factor influencing avoidance. Atlantic menhaden tested individually demonstrated the following responses: (1) avoidance increased with increasing delta T at 0.15 mg/l TRC; (2) minimal increase in avoidance at 0.00, 0.05, and 0.10 mg/l TRC as delta T increased; (3) greatest avoidance occurred at 0.10 mg/l TRC and 6 degrees C delta T; and (4) TRC was the most important factor influencing avoidance. A significant difference was found between avoidance models of the group and individual tests: greater avoidance generally occurred at most test conditions during the group tests. The data collected in this study showed the importance of testing methods when evaluating the avoidance responses of a strongly schooling species exposed to simultaneous chlorine and delta T conditions simulating a power-plant effluent.