Alarm response of Arius felis to chemical stimuli from injured conspecifics

The hardhead catfish (Arius felis) showed increased activity when subjected to water containing chemical cues of injured conspecifies. This response w as similar to the visually stimulated response to a model of a predatory fi sh. Arius felis also responded to chemical cues of injured sailfin mollies: (Poecilia latipinna) with increased activity, but this was less than in re sponse to conspecific chemical cues. A histological examination of Arius fe lis epidermis revealed that the alarm substance cells of marine catfish are similar to those of freshwater catfish. Responses to odors of injured indi viduals is common among ostariophysans, which art: mostly freshwater fishes . This is the first demonstration of an alarm reaction in a marine ostariop hysan.