Temperature-dependent otolith growth in Norwegian spring-spawning herring (Clupea harengus L.) larvae

Abstract

Norwegian spring-spawning herring larvae ( Clupea harengus L.) were reared at different temperature combinations in the laboratory, and marked twice with a fluorescent dye, alizarin complexone, to estimate otolith growth and increment deposition rate. A daily increment deposition rate was confirmed in the sagittae of larvae reared at 12 °C from day 16 (first marking age), while the apparent rate of increment formation of larvae reared at 4 °C was clearly less than one per day. A reduction in rearing temperature from 12 to 8 °C between days 16 and 30 (second marking age), significantly affected sagitta growth during the inter-mark period compared with those reared at 12 °C throughout. Similar somatic growth rates were observed in both groups temporarily reared at 8 °C between markings (about 6% day −1 ), but the otolith growth rate was more than four times higher in the group originating from 12 °C compared with the one originating from 4 °C. The body size versus otolith size relationship was temperature dependent, and larvae originating from different temperature regimes could be distinguished based on the differences in otolith growth pattern, but not based on differences in body size alone. The temperature-dependent otolith growth in herring larvae is expected to be of major importance for the observed differences in otolith microstructure patterns of herring stocks from different environments and regions in the field. However, this may be difficult to document in situations when larvae have low otolith growth and clear increment patterns are not present.