Larval Fish Age, Growth, and Body Shrinkage: Information Available from Otoliths

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Abstract
External and internal examination of Atlantic cod (Gadus morhua) otoliths for macrostructure and microstructure, by light and scanning electron microscopy, indicated daily rhythmic patterns. The first daily increment developed the day after hatching. Sagittae changed shape from spherical to oblong at 20 d and to crenulated at 50−60 d old. Cod were reared at three temperatures (6,8 and 10 °C), to provide a range of growth and developmental rates. Distinctive marks formed at yolk-sac absorption, initiation of feeding and settlement. It was possible to determine age and growth rate from otolith analyses. The relationship between otolith length and fish size was independent of growth rate; it followed a quadratic function for the smaller individuals (< 6.5 mm), and it was linear in individuals greater than 25 mm. Larval fish shrank considerably at death. The magnitude of shrinkage was dependent on larval length, and the elapsed time between death and fixation. Immediate fixation in ethanol resulted in minimal shrinkage. The relationship between fish length and otolith diameter may be used to correct for shrinkage associated with collection and death.