A relationship between the number of growth increments on the otoliths and age of larval and juvenile cod, Gadus morhua L. In: The propagation of cod Gadus morhua L.: an international symposium, Arendal, 14 - 17 June 1983
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A study of the relationship between the number of growth increments on the otoliths and age was based on larval and juvenile cod, Gadus morhua L., from laboratory and pond reared populations. Lapilli were larger than sagittae at hatching and remained so for approximately 25 days. Sagittae became significantly larger than lapilli at the end of the larval period. Major growth trends of the otoliths corresponded to the growth in standard length reported for the populations. Marked elongation along the anteroposterior axis and formation of marginal lobes started immedrately prior to metamorphosis. Comparison of otolith diameter and the diameter of the first, usually very distinct, growth increment indicated that zone formation started somewhat before hatchlng. The diameter of the first increment was higher in lapilli than in sagittae. The number of growth increments, as recorded using light microscopy, did not appear to be a constant function of larval age between hatching and metamorphosis at age 35-40 d. The larger of the otoliths at any given age, either the lapilli or the sagittae, showed higher increment numbers than the smaller. There was some indication that the rate of increment formation was related to the individual growth rate of the larva in this period. In addition to the primary increments recognized in the larval otoliths, composite broader zones appeared after metamorphosis. These broader zones were on the average formed daily at least until 140 days after hatching. The frequency of deposition of these structures did not appear affected by individual growth rate variation.