Recordings of pressure changes within the buccal and opercular cavities of lightly anaesthetized rainbow trout were made simultaneously with movement recordings of the lower jaw and operculum. Coughing movements during the normal rhythm were analysed and in addition coughing cycles evoked by the introduction of dyes into the mouth.
The different patterns recorded could be generally grouped into forward and backward types but a wide range was found. Information regarding the direction of water flow was obtained from analyses of the differential pressure waveforms and this also showed a range in different coughs. It is concluded that many variations of coughing grade into one another and the precise movements producing them and the afferent signals eliciting them remain to be investigated.