Estimation of metabolic rate from activity measured by recorders deployed on Japanese sea bass Lateolabrax japonicus

Abstract

Understanding the energy expenditure of top predators is important because a collapse in them could trigger trophic cascades through ecosystems. One such top predator, Japanese sea bass Lateolabrax japonicus, helps to balance the structure of the coastal marine ecosystem through predation. In this study, accelerometry was applied to the Japanese sea bass to estimate its energy expenditure under natural conditions. We attached accelerometers to five wild fish and measured metabolic rates such as the oxygen consumption rate (${\dot{\text{V}}\text{O}}_{ 2}$, mg O₂ kg⁻¹ min⁻¹) using a swim tunnel. Body beat frequency (BBF) was measured using the accelerometer. The BBF was correlated with the tail beat frequency (TBF) by analyzing video recordings. ${\dot{\text{V}}\text{O}}_{ 2}$ was related to swimming speed (U), TBF, and BBF. We estimated the standard (45.9 kJ kg⁻¹ day⁻¹) and active (124.0 kJ kg⁻¹ day⁻¹) metabolic rates when fish were not swimming and when they were swimming at the optimum swimming speed, respectively. The energy required to compensate for the above metabolic rates are between 83.3 and 275.6 kJ kg⁻¹ day⁻¹ using an assimilation efficiency of 0.7 and assuming that the growth rate is zero. These costs were comparable to consuming one or two prey fish per day (e.g., Japanese sardine: mean total length 155 ± SD 6 mm).