Abstract
During the pelagic larval phase of burbot Lota lota L., the pattern of otolith increments changes, showing three, clearly distinguishable growth sectors: a first sector with faint increments, difficult to enumerate, comprising an average (±S.D.) of 17˙5±6˙7 increments, a second sector with distinct increments comprising an average of 33˙1±7˙6 increments and a third sector where increments again become faint and difficult to enumerate. Laboratory experiments conducted in parallel to the field investigation showed that settlement occurs after the formation of this third, faint sector and is marked by the formation of numerous accessory growth centres within the range of three to five daily increments. There was a strong linear relationship between sagittal width and total length of the burbot (r2=0˙928) over the range examined. Significantly different growth rates were calculated for the three otolith sectors (faint, distinct, faint) in burbot larvae, indicating large environmental changes during their pelagic larval phase in Lake Constance. These results suggest that inshore migration of burbot larvae does not take place in the warm epilimnetic surface waters but via an alternative pathway, the cold hypolimnion or profundal zone.
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