DAILY GROWTH INCREMENTS IN THE OTOLITHS OF EUROPEAN SMELT OSMERUS-EPERLANUS LARVAE

Fish larvae of European smelt Osmerus eperlanus L. were collected in t he lower Elbe River, Germany, and aged using daily growth increments i n the otoliths. The otolith microstructure in the sagittae of larvae c aught within a 24 h period was examined and the daily pattern in incre ment formation was validated using the marginal increment technique. S melt larvae were also caught at a fixed station between April and May 1993. The formation of the first daily growth increment corresponds to the onset of exogenous feeding. The width of growth increments, radii , perimeters and areas of the otoliths were measured using an image an alysis system. A power function was fitted between otolith radius and standard length. Integrated somatic growth rate was estimated as 0.556 mm d-1 from the linear relationship between standard length and the n umber of daily growth increments enumerated from the sagittae. Otolith growth was best described using a 1-cycle Gompertz function. Back-cal culated hatching dates showed 2 main hatching batches during April 199 3 and the time span of the hatching was not longer than 16 d. There we re no significant differences among back-calculated otolith growths of 3 different hatching groups. At oxygen concentrations of <4.5 mg l-1, recent otolith growth showed high variability and negative values.