Repeated competition influences neural response, but not neurogenesis or physiology, in the fighting fish Betta splendens.

Authors

Jeremy A Spool, Alexander J A Heywood, Ruth E W Berganross, Elaine A Aquino, Temidayo D Bambe, Kelly J Wallace

Published in

The Journal of experimental biology. Sep 03, 2026. Epub Sep 03, 2026.

Abstract

Territorial competition has costs such as wounds received, energy spent, and elevated chronic stress. How does Betta splendens, a species that has been artificially selected for enhanced territorial aggression, maintain high levels of metabolically costly displays (gill flaring) over repeated days of territorial competition? Here we conducted two experiments. The first exposed male Betta splendens to a size-matched unresolvable competition (a mirror) daily for three weeks. We found that Betta splendens indeed maintain gill flaring throughout the competition schedule and exhibited no baseline stress impacts (measured via a scototaxis assay). We then exposed Betta splendens to one, two, or three weeks of competition and quantified cortisol levels, neurogenesis, and neural response in brain regions associated with social processing. We again found that Betta splendens showed consistently elevated gill flaring and again found no impacts on stress (measured via waterborne cortisol). Competition-exposed fish displayed increased neural response in the caudal supracommissural nucleus of the ventral telencephalon (Vs), a region that is homologous to the medial amygdala/bed nucleus of the stria terminalis and a central mediator of social decision-making. Neural response in this same region positively correlated with individual variation in gill flaring. Competition did not influence neurogenesis (doublecortin expression). Lastly, a measure of reproductive investment (gonadosomatic index) did not correlate to behavior but did correlate to cortisol levels, suggesting a cohesive physiological state related to reproduction in this species. Taken together, this work details the mechanisms that are relevant to the maintenance of costly aggressive behavior.

PMID:
42687851
Bibliographic data and abstract were imported from PubMed on 03 Sep 2026.

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