Low Luminosity Reduces Agonistic Behaviour of Nile Tilapia

ABSTRACT

In confrontations, many behaviors are based on visual information. To establish the importance of visual signals in the aggression of cichlid fish, we observed the behavior of groups in three juveniles of Nile tilapia (six groups in each condition), for 30 minutes under two extremes of light condition: high luminosity and low luminosity (dark condition for humans – only infrared light). The average number of bites and chases in the low luminosity was lower than observed in high luminosity. We conclude that the low luminosity condition diminishes but does not eliminate fights, and the fish can rely on nonvisual senses and low intensity of light to interact with conspecifics. The artificial high luminosity in artificial environments is potentially compromising welfare for increasing the number of agonistic interactions. Moreover, it is possible that in experimental designs studying behavior the high luminosity is a variable interfering in the conclusions about agonistic behavior in cichlid fish.

KEYWORDS:

• Aggressiveness
• light
• Oreochromis niloticus
• visual cues

Acknowledgments

We greatly appreciate the support of Professor Gilson Volpato, and for allowing the use of his laboratory facilities in the São Paulo State University (UNESP). We are also grateful to Professor Katsumasa Hoshino, for all valuable discussions and improvements during the development of this research. We would like to thank the National Council for the Improvement of Higher Education (CAPES) for the fellowship funding.

Highlights

• Low luminosity conditions diminish but do not eliminate fights of Nile tilapia.

• Fish do not rely only in visual senses to interact with conspecifics.

• Artificial high luminosity modulate aggressiveness in cichlid fish, compromising welfare.

• Studies investigating behaviour of cichlid fish in artificial environments should pay attention to the luminosity.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.