Abstract: The splendid alfonsino (Beryx splendens) is a deep-water, cosmopolitan fish species that is distributed around seamounts in all tropical and temperate seas, with the exception of the northeastern Pacific Ocean. Micro data loggers were attached to two captive splendid alfonsinos and data on depth, temperature and acceleration (two axes) were recorded over three continuous days. Body tilt angles were extracted from surging acceleration. Pectoral and caudal beat frequencies were determined from swaying acceleration. Both individuals descended to deeper water around sunrise. The first individual always occupied the deeper water, but the second individual inhabited the upper water. This is an indication of space partitioning. Pectoral Beat Frequency (PBF) had higher values than Caudal Beat Frequency (CBF) and was 1.45 times higher in the first individual and two times higher in the second individual. There was no difference in average body tilt angles between day and night in the first individual and values ranged from 20 to 40°. Average body tilt angles varied less in the second individual and averaged approximately 9° during the day and 0° during the night. Both the PBF and CBF were higher in the first individual, presumably to support the high tilt angles. This is the first time that PBF was extracted from the acceleration profile and separated from the CBF. We attributed the positive tilting behavior to the feeding behavior of the splendid alfonsino. This approves the possibility to attach the data logger to the deepwater fish splendid alfonsino and release to the open ocean.