Lower light intensity reduces larval aggression in matrinxã, Brycon amazonicus

•Environmental factor can be manipulated to improve conditions for fish species.•Aggressiveness is modulated by light intensity in matrinxã, Brycon amazonicus.•Lower light intensity reduced the display of aggressive interactions in matrinxã. Brycon amazonicus shows a high frequency of aggressive behavior, which can be a limiting factor in intensive farming systems. Environmental changes can modulate the social interactions of fish and reduce aggression during the different stages of production. Groups of three larvae at 12 h after hatching (HAH) were subjected to different levels of light intensity: low (17 ± 3 lx), intermediate (204 ± 12.17 lx) and high (1,613.33 ± 499.03 lx), with eight replicates for each level. The lower light intensity reduced the frequency of aggressive interactions and locomotor activity exhibited by the animals. Based on these results, light intensity modulates aggression in B. amazonicus larvae. Manipulation of this factor could improve the social conditions of this species during farming and contribute to the development of new production technologies.