The formalin EC50 for H. ecuadori infested gills for a 30-min exposure was 225 (146 –
204) mg l 1
, decreasing to 87 (79 – 130) and 47 (20 – 67) mg l 1 at 60 and 105 min,
respectively (Fig. 2). Taking in consideration the formalin LC50 values for bullseye puffer
fish, the EC50’s for H. ecuadori yield a therapeutic index of 5 at 30 min and of 11 at 60 min.