Russian sturgeon (Acipenser gueldenstaedtii) is commercially important in Korea because its caviar is highly prized. Although the early ontogeny of the species has been described, behavioral modifications in response to various light intensities or diel photoperiodicity patterns have not been studied extensively. The objective of the present study was to examine the behavioral characteristics of hatchery-produced A. gueldenstaedtii prelarvae over a diel photoperiodic cycle. During a diel light cycle comprising 16 h of daylight (450 lx), 4 h of dim light (10 lx), and 4 h of darkness (< 1 lx), newly hatched A. gueldenstaedtii prelarvae exhibited negative phototaxis in daylight (day 0-day 2), and this early behavior was not significantly affected by changes of light intensities. Rheotactic and non-rheotactic aggregation into schools was typical between days 3 and 6. Under the diel light cycle conditions described, rheotaxis was not influenced by environmental light intensity as much as non-rheotactic schooling behavior. Post-schooling behavior, which progressed from day 7 to day 8, did not change significantly during the diel light cycle. The data from the present study could be of practical value in developing a visual guide for assessing the fitness and quality of Russian sturgeon prelarvae under diel light cycle conditions in hatcheries.

Sturgeons belonging to Acipenseriformes represent the ancient lineage of actinopterygian fishes (ray-finned fishes), often referred to 'living fossils' (Birstein et al., 1997; Web and Doroshov, 2011). Due to their primitive phylogenetic position, sturgeons have been considered as useful models for various evolutionary researches (Kim et al., 2005; Cho et al., 2007; Kim et al., 2019a). In addition, sturgeons, as the source of caviar, have been valuable Behavioral characteristics of a chondrostean sturgeon species Acipenser baerii prelarvae in response to different environmental light intensities in a diel photoperiodic cycle