Fig. 4. (A) Response to a 2.5 µmol N l^-1 mixture (1:1:1) of L-proline, L-alanine and L-glycine (Amino Acids; PAG); 2.5 µmol N L^-1 PAG with 25 µmol N L^-1 ammonia-N (Amm + Amino acids); 2.5 µmol N l^-1 PAG with 25 µmol N l^-1 ammonia-N + urea-N (1:1; A/U mix + Amino acids); and toadfish homogenate (positive control). Significant differences were found between treatment groups (F=7.393, P<0.001, N=8) as indicated by the different letters. (B) Behavioral assay to measure response to a 2.5 µmol N l^-1 mixture (1:1:1) of PAG; 2.5 µmol N l^-1 PAG with 25 µmol N l^-1 urea-N; and seawater controls. Significant differences were found (F=9.293, P=0.005, N=6). Controls, the tabulation of the behavioral index, data transformations and subsequent statistics were identical to Fig. 2.