Fig. 2. Behavioral responses to 25 µmol N l^-1 ammonia-N (Amm), urea-N, a 1:1 ammonia-N/urea-N mixture (A/U Mix) and controls during 60 min observation periods. Clarified toadfish homogenate, a positive control, was delivered last. The behavioral index is the sum of snapper responses characterized by entry into the shelter, passing 0-25 cm from shelter opening, passing 25-50 cm from shelter, and hovering while visually scanning shelter interior, which were awarded 5, 2, 1 and 1 points, respectively. The baseline reflects activity prior to odorant delivery. Data were log(x+1) transformed for equal variance. The paired t-test was used to examine each treatment and its alternate seawater control, and significant differences are denoted by an asterisk. Differences among treatment group where determined with a repeated measures ANOVA (F=14.509, P<0.001, N=10) and significantly different groups are indicated by different letters.