Possible fitness costs of high and low standard metabolic rates in larval herring Clupea harengus, as determined by otolith microstructure

Abstract

In a laboratory experiment, we sought to identify effects of metabolic rate on the sur-vival and growth of individual larvae of Clupea harengus L. The size of the otolith at hatch was used as a measure of standard metabolic rate (SMR) to test the hypotheses that (1) larvae with a low SMR survive longer than larvae with a high SMR during starvation, and (2) larvae with a high SMR grow faster than larvae with a low SMR during periods of high food availability. Herring larvae were reared in replicate tanks with either high, low or no food. Dead larvae were sampled twice daily and live larvae were sampled weekly. The longevity of the larvae was unrelated to their SMR in all treatments and, therefore, the first hypothesis was rejected. However, a positive correlation between otolith size-at-hatch and larval dry weight after hatch (r = 0.48, df = 100, p < 0.001) suggested that the hypothesised negative effect of high SMR on longevity may be offset by higher energy reserves (i.e. more yolk) in these larvae. In both high-level food groups there was a significant association between sagitta growth and sagitta size-at-hatch (H1, χ2 = 5.17, df = 1, p = 0.023; H2, χ2 = 4.75, df = 1, p = 0.029) and, therefore, the second hypothesis was supported. However, large otolith size-at-hatch was also observed in slow-growing larvae, hence a high SMR may be a prerequisite for fast growth, but does not necessarily result in fast growth. © Inter-Research 2007.