The Lusitanian toadfish Halobatrachus didactylus (Bloch & Schneider) (Batrachoididae) is a well-known sound producer that has an unusual large acoustic repertoire for fish. This repertoire consists so far of five distinct sound categories: boatwhistles, grunt trains, croaks, double croaks and a mixed grunt–croak call. Sixteen males that spontaneously occupied artificial concrete nests placed in the intertidal zone of the Tagus estuary (Portugal) were recorded over 8 days in June/July 2006. During the analysis of the recordings new sound emissions were found. Long grunt trains that sounded to the human ear like a running engine were heard. These sounds differ from the normal grunt trains by having a lower amplitude, a much longer duration (tens of seconds versus <1 second) and more grunts per call. Other new sound emissions (e.g. triple croaks) were also registered but were heard less frequently. The incidence of the various sound types is given.
