Agonistic trials with mirrors do not elicit the same aggressiveness of a real trial in the matrinxã fish,Brycon amazonicus(Spix & Agassiz, 1829)

Abstract

This study tested the efficacy of mirror trials in studying aggressiveness in the matrinxã fish, Brycon amazonicus. The hypothesis was that a mirror would elicit an aggressive response in B. amazonicus juveniles, but show different behavioral and physiological profiles than those observed in trials with real opponents. Fish were tested using either a mirror trial (n = 7) or a real trial (n = 7), that is, placed alone with a mirror or paired with a same-sized opponent, respectively. All trials lasted for 20 min and took place in 96-L aquaria with water temperatures of 28°C. Fish in mirror trials exhibited less locomotion (mirror: 423.3 ± 39.1; real trial: 735.1 ± 31.9; p < .001), rushed less against the opponent (mirror: 3.1 ± 2.3; real trial: 39.6 ± 5.1; p < .001) and showed less escalation of aggressive behavior compared to the winner of a real trial. Regarding the physiological parameters, despite similar cortisol responses (mirror: 84.2 ± 13.8 ng/ml; real trial: 77.2 ± 16.9 ng/ml; p = .757), the fish that fought against a mirror had lower levels of plasma glucose than those of fish that fought against a real opponent (mirror: 76.8 ± 3.6 ng/dl; real trial: 103.8 ± 10.1 ng/ml; p = .037). This lower energy mobilization might be due to a lower cost of the fight in the absence of an opponent that flees from attacks, as the locomotion and number of rush totals were also lower in the mirror trials. This pattern of less locomotion is probably common in mirror trials because the opponent is always limited to one side of the arena. If the energetic cost is one of the factors that can determine the outcome of a fight, and if mirror trials do not evoke the physiological response observed in a real fight, the use of mirror trials must be reviewed in studies that consider the physiological responses.

Acute fluoxetine treatment increases aggressiveness in juvenile matrinxã (Brycon amazonicus)

“…This result was contradictory to our hypothesis, which was based on several studies showing an inhibition of aggression after FLX treatment (Perreault et al 2003;Lynn et al 2007;Kania et al 2012;Forsatkar et al 2013). Furthermore, cortisol levels after 20 min of fighting with a same-sized conspecific intruder were consistent with the literature (Wolkers et al 2014;Serra et al 2016), with no significant difference between the treatments.…”

“…Fighting is stressful for fish (Øverli et al 1999, 2004), and even after 12 h of FLX treatment, matrinxãs were able to properly respond to this stressor, reaching cortisol levels that were similar to the control group and consistent with cortisol levels observed in matrinxã (control fish) after a similar fight paradigm demonstrated in previous studies (Wolkers et al 2014;Serra et al 2016). In jundiá Rhamdia quelen juveniles, a short (17 min) exposure to FLX in the water also altered the behavior (had an anxiolytic effect) without impairing the stress response (Abreu et al 2016).…”

Through a glass darkly? Divergent reactions of eight Lake Tanganyika cichlid species towards their mirror image in their natural environment

“…In such cases, mirror presentations might miss crucial parts of the communication occurring during aggressive encounters. Accordingly, several studies showed diverging aggressive responses of fishes tested against mirror images or live opponents (Arnott et al, 2016;Balzarini et al, 2014;Elwood et al, 2014;Li, et al, 2018a;Li, et al, 2018b;Ruzzante, 1992;Serra et al, 2017;Verbeek et al, 2007). Furthermore, even if aggressive behaviours towards a mirror image and a live opponent are comparable, differences in hormonal response or brain activity indicate that contestants discriminate between a conspecific and a mirror image.…”