Effect of aquaria water renewal on the aggressive behavior and recovering of the dominance hierarchy in Acará-Bandeira

Abstract

Social animals interact aggressively to establish territories and dominance hierarchy. To avoid constant fighting and reduce chances of injuries, they keep a social position through "displays" and other signs. In fish, chemical signs, which indicate the social position, are released into the water and are perceived by conspecifics. However, water renewal in aquariums and breeding tanks is required to remove food residues and organic leftovers that accumulate in the environment. This procedure reduces the chemical signs released by individuals and impairs communication between animals, disturbing social status recognition and increasingly aggressive interactions among individuals. This may increase physical injuries, energy expenditure, and the level of social stress in animals. A previous study with Nile tilapia showed that aggressive interactions increased after 50% of the aquarium water renewal. Thus, it's possible that a less water level renewal attenuates the effects on the aggressive interactions and, even the hierarchy stability is broken, it can be temporary and present a quick recovering. Then, the aim of this study is to test if the water renewal effects on aggressiveness and social stability in angelfish depend on the amount of water renewed. Initially, there will be tested if there is an effect on the renewal of 25% and 50% of water. In addition, we will test if the time to restore the hierarchy stability occurs faster when less water is renewed. The novelty of this work lies in the water's amount and its effect on the dominance hierarchy recovering in fish. There will be performed three treatments (n = 15 each) composed of aquaria with three young animals each: 1) Water renewal 25%; 2) Water renewal 50%; 3) Without water renewal (control). The animals will be grouped together for five days. During the first 3 days, aggressive behavior will be filmed (10 min/day) to assess the dominance hierarchy's stability. By the fourth day, the water exchange or the water removal-and-return (same water)will be done. The behavior will be filmed (10 min) before the renewal, after the renewal, 1 hour, 2 hours, 3 hours, and 24 hours after renewals (5th day of grouping). Data will be tested for normality and homogeneity of variances. If parametric, frequency and duration of aggressive interactions between the records will be compared by ANOVA for repeated measures in mixed models, being treatments the categorical factors and aggressiveness, the repeated measures. The stability of the dominance hierarchy will be inferred from the correlation of social status between periods after Spearman's rank correlation test.(AU)