Olfactory search tracks in the Antarctic fish Trematomus bernacchii

Video observations were made of benthic fish approaching the source of an o lfactory plume. Fish (identified as Trematomus bernacchii from their "saddl eback" markings) all approached the source from downstream, with relatively straight approach tracks. When the plume was made visible it showed a dist inct concentration of the stimulus at the point of release, and a plume whi ch extended down-stream with a rapidly decreasing stimulus gradient. Comput er simulations were made that could generate search strategies based on che mical gradient information, and current (rheosensory) information alone or in combination. Only the combination of chemosensory and rheosensory inform ation provided an adequate match to the observed approach tracks.