Otolith Microstructure during the Early Life-History Stages of Brown Trout: Validation and Interpretation

Abstract

We examined the extent to which otolith microstructure provides an accurate estimate of age, growth, and early life history transitions during the period between hatching and 1 week after emergence in Brown Trout Salmo trutta exposed to natural variations in ambient water temperature. All fry analyzed possessed a prominent check on the observed date of hatching. After hatching, daily growth increments were visible on sagittal otoliths. There was no evidence for the formation of an emergence check mark and no statistically significant evidence that emergence and daily temperature fluctuations interacted to form check marks. However, daily temperature fluctuations may influence the formation of check marks, largely based on an observed increase in the proportion of fish possessing checks on the days following the two largest temperature fluctuations observed during the experiment. There was no evidence that feeding or stressing emergent fish contributed to the formation of an emergence check mark. The observed proportionality of somatic and otolith growth in conjunction with daily growth increments and the formation of a prominent hatch mark provides the opportunity to back-calculate somatic length distributions and to document the hatching, dispersal, growth, and survival of the early life history stages of Brown Trout in nature. Received May 3, 2012; accepted October 29, 2012