# Correlation between bioluminescent blinks and swimming behavior in the splitfin flashlight fish Anomalops katoptron

## TL;DR

This study explores how the splitfin flashlight fish uses its bioluminescent blinks to control its swimming behavior and coordination within a group.

## Contribution

The study reveals a novel behavioral trait linking light organ occlusion with changes in swimming direction during shoaling.

## Key findings

- Flashlight fish showed higher swimming speeds and curved paths during light organ occlusion.
- The largest changes in swimming direction occurred when the light organs were darkened.
- Before reactivating their light organs, fish adapted to a nearly straight movement direction.

## Abstract

The light organs of the splitfin flashlight fish Anomalops katoptron are necessary for schooling behavior, to determine nearest neighbor distance, and to feed on zooplankton under dim light conditions. Each behavior is coupled to context-dependent blink frequencies and can be regulated via mechanical occlusion of light organs. During shoaling in the laboratory individuals show moderate blink frequencies around 100 blinks per minute. In this study, we correlated bioluminescent blinks with the spatio-temporal dynamics of swimming profiles in three dimensions, using a stereoscopic, infrared camera system.

Groups of flashlight fish showed intermediate levels of polarization and distances to the group centroid. Individuals showed higher swimming speeds and curved swimming profiles during light organ occlusion. The largest changes in swimming direction occurred when darkening the light organs. Before A. katoptron exposed light organs again, they adapted a nearly straight movement direction.

We conclude that a change in movement direction coupled to light organ occlusion in A. katoptron is an important behavioral trait in shoaling of flashlight fish.

The online version contains supplementary material available at 10.1186/s12862-024-02283-6.