Short-term decoupling of otolith and somatic growth induced by food level changes in postlarval Baltic sprat, Sprattus sprattus

Abstract

We studied the effects of food level changes on otolith and somatic growth in postlarval Baltic sprat reared initially for a period of 11 days under zero, low, and ad libitum feeding conditions. During a subsequent 11 day period, feeding regimes were reversed in half of the low and ad libitum feeding treatments, and starved fish were re-fed ad libitum rations. Somatic growth rates under low and ad libitum food rations ranged between 0.15–0.22 mm day−1 and 0.48–0.63 mm day−1, respectively, and led to significant differences in length and weight between feeding regimes. Previously starved fish, however, grew only 0.25–0.28 mm day−1 under ad libitum conditions. During the first period, significant linear relationships were found for otolith v. length and v. weight growth across all treatments. After changing feeding regimes, increment widths failed to significantly predict somatic growth for 9 days, after which a significant relationship between otolith and somatic growth became re-established. Recent otolith growth was a good predictor of fish condition after the first, but not after the second period. The results suggest that perturbations in environmental conditions can temporarily decouple otolith from somatic growth in postlarval sprat, which needs to be considered in field studies.