Escape responses of the Japanese anchovy Engraulis japonicus under elevated temperature and CO2 conditions

Abstract

An increasing number of papers have been published on the effects of ocean acidification and warming on fishes over the last several years. However, there is little information on how these environmental changes affect the swimming behavior of fish. This study examined the escape response under elevated CO2 concentration and temperature of the Japanese anchovy Engraulis japonicus. Following acclimation to four conditions (CO2 400/1000 ppm, temperature 15/19 °C) for 1 month, the fish were tested for escape response through kinematic analysis of startle reactions to a mechanical stimulus. The response was recorded with a high speed video camera of 500 frames per second. The result showed turning rate was significantly higher at 19 °C than at 15 °C. Neither CO2 nor temperature affected the kinematic parameters analyzed (the escape trajectory, swimming velocity, acceleration, escape direction, or frequency of single and double bends), with the exception of the turning rate that was significantly higher at 19 °C than at 15 °C. However, we must clarify how future oceanic environmental changes affect escape responses of schooling fish and prey-predator interactions under more rigorous experimental conditions, to elaborate our prediction capacity for the trajectory of anchovy populations and thereby assess possible implications for anchovy fisheries.