Metabolic Rates in Early Life History Stages of Elopomorph Fishes

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Abstract
The respiratory electron transport system (ETS) assay was used to estimate metabolic rates in four species of eel (Anguilliformes: Ophichthidae and Congridae) leptocephali (Myrophis punctatus, Ophichthus sp., Hildebrandia flava, and one unidentified congrid) and the bonefish (Albuliformes: Albulidae: Albula sp.). Wet-weight-specific ETS values in whole-body homogenates, assayed at physiological temperatures, ranged from 4-20 {mu}-at O h-1 (g wet wt)-1. Arrhenius activation energies (Ea) ranged from 11.0-15.7 kcal mole-1. Both wet-weight-specific ETS activity and oxygen consumption rate increased approximately fivefold during metamorphosis of leptocephali of Albula sp. Wet-weight-specific ETS activity showed little change as leptocephali of M. punctatus transformed into glass eels, but increased about fivefold as glass eels metamorphosed into elvers. No significant difference was found in ETS activity measured in fresh early metamorphic leptocephali of Albula sp. and leptocephali that had been stored frozen at -70{deg}C for up to 15 months. The data suggest that metabolic rates are low in leptocephali, which implies that the demand for nutrients is also relatively low. We argue that the apparent diet of these larvae seems capable of providing a sufficient supply of nutrients under these conditions.

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