Daily rhythms of locomotor activity and the influence of a light and dark cycle on gut microbiota species in tambaqui (Colossoma macropomum)

This study aimed to assess the daily rhythms of locomotor activity and to quantify bacteria populations in the tambaqui digestive tract during light and dark periods. Photoelectric cells and a recording computational system were used to quantify the locomotor activity, and the existing Gram-positive and Gram-negative bacteria populations were evaluating during the daytime and night-time periods. The results showed a typical pattern for nocturnal locomotor activity (91%), and lower percentages of Gram-positive 6?×?10³, 24% and Gram-negative cocci (approximately 38%) were observed during the same periods compared with the diurnal period (76 and 62%, respectively). Additionally, lower percentages of Gram-positive (42%) and Gram-negative (44%) Bacillus were observed during the same periods compared with the diurnal period (29?×?10⁶ CFU/g, 58% and 23?×?10⁶ CFU/g (56%), respectively). These data should be considered when animals are subjected to high stress loads for more appropriate management strategies and collaborating with future studies of what is the best schedule to vaccinate or provide probiotics to fish.