The feeding behaviour of medium sized (155.25 +/- 27.98 cm, n = 8) whiting, Merlangius merlangus, under laboratory conditions was investigated with continuous food availability. This investigation was made using both natural, Sprattus sprattus, and artificial diet which was monitored with a periodogram analysis obtained by a newly developed demand feeding unit. The return of appetite of large whiting (305.85 +/- 056.90 cm) was also studied. Medium size whiting consumed 5.29 g (wet weight)/day corresponding to 3.41% body weight, approximately three sprats of 1.88 g each. The return of appetite after a single meal was found to follow the gastric emptying curve closely. If food is not offered directly but made available through demand feeding, the whiting feed rhythmically (every 21 h); under these conditions, it was estimated that feeding activity returns when the stomach is 40% full. (C) 1998 Elsevier Science B.V.