Journal of Comparative Physiology A

, Volume 205, Issue 6, pp 867–880 | Cite as

Dietary l-tryptophan modulates agonistic behavior and brain serotonin in male dyadic contests of a cichlid fish

  • L. Morandini
  • M. R. Ramallo
  • M. F. Scaia
  • C. Höcht
  • G. M. Somoza
  • M. PandolfiEmail author
Original Paper


Although some studies have investigated the effects of dietary l-tryptophan on agonistic behavior, research on adult fish specimens is still lacking. Moreover, submissive behaviors have been generally overlooked. We focused on agonistic behavior between males of the cichlid fish Cichlasoma dimerus, in dyadic encounters held in a novel context after being fed or not with an l-tryptophan enriched diet (TRP) for 2 weeks. We arranged three different dyads: control/control (control conditions: not TRP enriched), control/TRP, and TRP/TRP. We also registered the response of the brain serotonergic system in four brain regions. TRP/TRP dyads showed higher latencies to first attack, lower overall aggression, and lower proportions of bites and passive copings (submissive display) compared to control/control. TRP dominant males performed fewer bites with respect to controls, and subordinate males opposed to TRP males showed fewer passive copings. Higher serotonergic activities were found in subordinates’ optic tectum and in the telencephalon and preoptic area/hypothalamus of TRP males. Altogether, results point out that dietary l-tryptophan reduced males’ motivation to attack and dominant aggression, which consequently influenced subordinate agonistic repertory. In addition, males within TRP/TRP dyads showed a switch in their behavioral agonistic repertory. These behavioral outcomes were probably due to modifications at brain serotonergic functioning.


Agonistic behavior Brain Cichlids l-Tryptophan Serotonin 









Control dietary protocol


CTL vs. TRP male


CTL vs. CTL male




Total body length


Optic tectum


Preoptic area/hypothalamus








l-Tryptophan supplemented dietary protocol


TRP vs. TRP male



Our research has been funded by the following grants: Agencia de Promoción Científica y Tecnológica (Grant PICT 1482) and Universidad de Buenos Aires (Grant UBACyT 20020130200038BA). We would particularly like to thank Mariel Tripoli for her statistical recommendations and two anonymous reviewers for numerous meaningful suggestions.

Complaince with ethical standards

Ethical standards

All experiments were conducted in conformity with international standards on animal welfare, as well as being in accordance to institutional (Comisión Institucional para el Cuidado y Uso de Animales de Laboratorio, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires) and national (Comité Nacional de Ética en la Ciencia y la Tecnología, MINCyT, Argentina) regulations. All procedures were in compliance with the Guide for Care and Use of Laboratory Animals (National Research Council 2011).


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • L. Morandini
    • 1
  • M. R. Ramallo
    • 1
  • M. F. Scaia
    • 1
  • C. Höcht
    • 2
  • G. M. Somoza
    • 3
  • M. Pandolfi
    • 1
    Email author
  1. 1.Laboratorio de Neuroendocrinología y ComportamientoDBBE, FCEN, UBA e IBBEA, CONICET-UBABuenos AiresArgentina
  2. 2.Departamento de Farmacología, Facultad de Farmacia y BioquímicaUniversidad de Buenos AiresBuenos AiresArgentina
  3. 3.Instituto Tecnológico de Chascomús (CONICET-UNSAM)Buenos AiresArgentina

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