A comparison of primary growth rings in otoliths from Sprattus sprattus from Norway and Sardinella spp. from Sri Lanka. In: Flødevigen rapportserie no 1, 1986
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The present paper describes the otolith structure and the ring deposition pattern in 0-group sprat (Sprattus sprattus). This is compared with that of Sardinella from tropical waters. Age was estimated by using the primary growth rings in the otoliths and the estimated age was used to calculate the spawning time and to estimate growth. Otolith structure and ring deposition were found to be similar in sprat and Sardinella. In sprats, the number and the thickness of the rings in the nuclear region seemed to vary with the time of spawning. This indicated a difference in the age of metamorphosis of sprat larvae. In Sardinella, however, the period of metamorphosis was shown to be a species-specific characteristic. Back-calculated birth dates of sprat generally suggested a protracted spawning from February to July with a peak in April - June. Estimated spawning in Nordfjord (west Norway) is confirmed by the known spawning curves. The calculated spawning for other locations too, in genereal agrees well with the known spawning. The resulted growth estimates of sprat with K = 0.82 corresponds to previous estimates. The results (growth and birth dates) verify the daily periodicity of rings. The similarity of the otolith structure of sprat to that of Sardinella and herring (Clupea harengus) also indirectly validates the hypothesis that the rings are formed daily.