Influence of Rearing Temperature and Feeding Regime on Otolith Increment Deposition in Larval Ciscoes

Larval ciscoes Coregonus artedi were reared in the laboratory from eggs collected in Lake Superior to validate the use of otolith microstructure for estimating age in days. Throughout a 75-d period, water temperatures in two laboratory streams were increased progressively (from 5.6 degrees C to 7.0 degrees C and from 6.1 degrees C to 12.3 degrees C), mimicking the range larvae would probably experience in Lake Superior. Otolith increments were deposited at a rate not statistically different from one increment per day, starting from approximately 28 d posthatch, which was near the time of complete yolk sac absorption. Feeding frequency (twice daily, once daily, alternate days, and food deprivation) did not affect the prominence of subdaily marks (i.e., bands occurring in between daily increments), but a 5-d period of food deprivation reduced increment contrast in some larvae. The reduced rations partly explained lower growth rates among larvae, and larvae with lower growth rates could not be aged as accurately by otolith analysis. An accessory check mark was induced by a,sudden decrease in temperature but not by a reciprocal increase in temperature (between 6.9 degrees C and 12.3 degrees C). These results indicate the potential use of otolith analysis for aging larval ciscoes but are strongly cautionary about the method's limits at reduced growth rates. The results also suggest that patterns in otolith microstructure can be used to track shifts in environmental conditions, particularly temperature and feeding success, which may influence growth and survival of ciscoes during early life.