Growth differences in larval plaice Pleuronectes platessa in the Southern Bight of the North Sea as indicated by otolith increments and RNA/DNA ratios

Somatic and otolith growth of larval plaice Pleuronectesplatessa L. was studied under field and experimental conditions. Rearing experiments at 6 and 9C demonstrated a relation between somatic and otolith growth, and a larger size-at-stage for fast growing larvae. In the field, 2 groups of larval plaice were caught at dates 2 wk apart in the southern North Sea in March 1988, and growth was examined using 4 methods: size-at-age, size-at-developmental stage, otolith increment widths, and RNA/DNA ratios. All methods yielded the same result. Larvae captured on 22 March had been growing faster then larvae caught on 8-9 March. Larvae from 22 March were larger at the same age, and had attained a larger size at the same developmental stage. Slow growth led to relatively large otoliths. Analysis of otolith increments showed these growth differences to be of recent origin, a conclusion that is supported by higher RNA/DNA ratios of the late group. Temperature differences were too small to explain this difference, and temporary starvation or food limitation inay have occurred.