The 'earthy' and 'muddy' o¡-£avours in pond-reared ¢sh are due to the presence of geosmin or 2-methylisoborneol in the £esh of the ¢sh. Similar o¡-£avours have been reported in ¢sh raised in recirculating aquaculture systems (RAS); however, little information is available regarding the cause of these o¡-£avours. Our hypothesis was that earthy and muddy o¡-£avour compounds, found previously in pondraised ¢sh, are also responsible for o¡-£avours in ¢sh raised in RAS. In this preliminary study, we examined water, bio¢lms in RAS and ¢llets from cultured arctic charr known to have o¡-£avours and requiring depuration using instrumental [solid-phase microextraction procedure and gas chromatograph-mass spectrometry (GC-MS)] and human sensory analyses. Geosmin was present in the samples taken from the bio¢lter and on the side walls of the tanks. Twomethylisoborneol was only found in low levels in the samples. The GC-MS results indicated the presence of geosmin in the ¢llets (705 ng kg À 1 ), but lower levels were found in the water (30.5 ng L À 1 ). Sensory analyses also detected an earthy £avour (i.e., geosmin presence) in the ¢llets, and, therefore, it appears that geosmin is the main compound responsible for the o¡-£avour in RAS. Further studies are being performed to identify the microorganisms responsible for geosmin production in RAS.