a behavioral bioassay method was developed to examine the effects of ethanol on the reproductive success and behavior of flagfish (jordanella floridae). reproductive behavior was divided into eight categories; egg tending; nesting; t-circling; chasing a faded female; spawning; guarding; chasing; and inattentive behavior. the dominant male in each tank was observed for ten minutes daily for five days before and after ethanol exposure. the data was examined to determine the frequency with which each behavior occurred, the percent of the total frequency that each behavior represented, the total time spent at each behavior, and the sequential order in which the behaviors occurred. total frequency, the number of times the fish switched from one behavior to another, was reduced when the fish were exposed to concentrations of ethanol ranging from 0.5 to 3.0 g/liter. when behavior was analyzed with respect to the eight behavioral categories, it was found that no single behavior contributed to the decline but rather the number of times a fish engaged in each behavior was reduced. accompanying this reduction in activity was an increase in inattentive behavior. when sequences of behavior were examined, no significant change occurred even at the higher ethanol concentrations. fewer eggs were recovered from adults exposed to 2.0 and 3.0 g/liter. of the eggs produced, hatchability and larval survival exceeded 94% and 90%, respectively, at all concentrations tested. it was concluded that the reduction in spawning activities at concentrations of 1.5, 2.0, and 3.0 g/liter ethanol was due to the overall reduction in activity. it appears that the dominant male must maintain a minimal threshold of activity to successfully spawn.