Water temperature affects aggressive interactions in a Neotropical cichlid fish

Changes in water temperature may affect the aggressive behavior of aquatic organisms, such as fish, either by changing some physiological mechanisms or by increasing the probability of encounters between individuals as a result of variation in their swimming activity. In our study, we evaluated the influence of increasing and decreasing temperature on the aggressive behavior of the Neotropical cichlid fish Cichlasoma paranaense. Firstly, we tested the critical thermal maximum (CTMax) tolerated by this species. Then, we tested the effect of decreasing or increasing the water temperature in 6o C (starting at 27° C) on the aggressive interactions of fish under isolation or housed in groups. We found a CTMax value of 39° C for C. paranaense. We also observe that a 6° C decrease in water temperature lowers swimming activity and aggressive interactions in both isolated and group-housed fish, as expected. On the other hand, the increase in temperature had no effect on the fish's aggressive behavior, neither for isolated nor for grouped fish. We concluded that C. paranaense shows high tolerance to elevated temperatures and, in turn, it does not affect aggressive behavior. Nevertheless, we cannot dismiss possible effects of elevated temperatures on aggressive interactions over longer periods.(AU)

Mudanças na temperatura da água podem afetar o comportamento agressivo de organismos aquáticos, como peixes, seja alterando alguns mecanismos fisiológicos ou aumentando a probabilidade de encontros entre os indivíduos como um resultado da variação na sua atividade natatória. Em nosso estudo, nós avaliamos a influência do aumento e da diminuição da temperatura sobre o comportamento agressivo do peixe ciclídeo neotropical Cichlasoma paranaense. Primeiramente, nós testamos a temperatura crítica máxima (CTMax) tolerada por essa espécie. Depois disso, nós testamos o efeito de reduzir ou aumentar a temperatura da água em 6° C (a partir de 27° C) sobre as interações agressivas de peixes sob isolamento ou alojados em grupos. Nós encontramos um valor de CTMax de 39° C para C. paranaense. Nós também observamos que uma redução de 6° C na temperatura da água diminui a atividade natatória e as interações agressivas tanto em peixes isolados quanto agrupados, como esperado. Por outro lado, o aumento na temperatura não teve efeito no comportamento agressivo dos peixes nem isolados, nem agrupados. Nós concluímos que C. paranaense apresenta alta tolerância a temperaturas elevadas, e que isso, por sua vez, não afeta o comportamento agressivo. No entanto, nós não podemos descartar possíveis efeitos de temperaturas elevadas sobre interações agressivas durante longos períodos.(AU)

Water temperature affects aggressive interactions in a Neotropical cichlid fish

Changes in water temperature may affect the aggressive behavior of aquatic organisms, such as fish, either by changing some physiological mechanisms or by increasing the probability of encounters between individuals as a result of variation in their swimming activity. In our study, we evaluated the influence of increasing and decreasing temperature on the aggressive behavior of the Neotropical cichlid fish Cichlasoma paranaense. Firstly, we tested the critical thermal maximum (CTMax) tolerated by this species. Then, we tested the effect of decreasing or increasing the water temperature in 6o C (starting at 27° C) on the aggressive interactions of fish under isolation or housed in groups. We found a CTMax value of 39° C for C. paranaense. We also observe that a 6° C decrease in water temperature lowers swimming activity and aggressive interactions in both isolated and group-housed fish, as expected. On the other hand, the increase in temperature had no effect on the fish's aggressive behavior, neither for isolated nor for grouped fish. We concluded that C. paranaense shows high tolerance to elevated temperatures and, in turn, it does not affect aggressive behavior. Nevertheless, we cannot dismiss possible effects of elevated temperatures on aggressive interactions over longer periods.(AU)

Mudanças na temperatura da água podem afetar o comportamento agressivo de organismos aquáticos, como peixes, seja alterando alguns mecanismos fisiológicos ou aumentando a probabilidade de encontros entre os indivíduos como um resultado da variação na sua atividade natatória. Em nosso estudo, nós avaliamos a influência do aumento e da diminuição da temperatura sobre o comportamento agressivo do peixe ciclídeo neotropical Cichlasoma paranaense. Primeiramente, nós testamos a temperatura crítica máxima (CTMax) tolerada por essa espécie. Depois disso, nós testamos o efeito de reduzir ou aumentar a temperatura da água em 6° C (a partir de 27° C) sobre as interações agressivas de peixes sob isolamento ou alojados em grupos. Nós encontramos um valor de CTMax de 39° C para C. paranaense. Nós também observamos que uma redução de 6° C na temperatura da água diminui a atividade natatória e as interações agressivas tanto em peixes isolados quanto agrupados, como esperado. Por outro lado, o aumento na temperatura não teve efeito no comportamento agressivo dos peixes nem isolados, nem agrupados. Nós concluímos que C. paranaense apresenta alta tolerância a temperaturas elevadas, e que isso, por sua vez, não afeta o comportamento agressivo. No entanto, nós não podemos descartar possíveis efeitos de temperaturas elevadas sobre interações agressivas durante longos períodos.(AU)

The effect of increased light intensity on the aggressive behavior of the Nile tilapia, Oreochromis niloticus (Teleostei: Cichlidae)

Animals show behavioral and physiological changes that emerge in response to environmental perturbations (i.e., emergency life-history stages). In this study, we investigate the effects of light intensity on aggressive encounters and social stability in groups of adult male Nile tilapia, Oreochromis niloticus (Linnaeus, 1758). The study compared the behavior observed under low (280.75 ± 50.60 lx) and high (1394.14 ± 520.32 lx) light intensities, with 12 replicates for each treatment. Adult fish were isolated in 36-L aquaria for 96 hours, and three males were grouped for 11 days in 140-L aquaria. Agonistic behavior was video-recorded (10 min/day) on the 3rd, 5th, 7th, and 9th day to quantify aggressive interactions and social stability. There was an effect of light intensity and day of observation on the total number of agonistic behaviors performed by the fish group. Besides, increased frequency of aggressive interactions (the sum of the four sessions) by the alpha, beta and gamma fish occurred at the higher light intensity. The dominance ranks of the fish remained unchanged across the observation sessions under both the low and high light intensities. We concluded that enhanced light intensity has a cumulative effect that increases the aggressiveness of the Nile tilapia but that this effect is not sufficiently strong to destabilize the social hierarchy.

The effect of increased light intensity on the aggressive behavior of the Nile tilapia, Oreochromis niloticus (Teleostei: Cichlidae)

Animals show behavioral and physiological changes that emerge in response to environmental perturbations (i.e., emergency life-history stages). In this study, we investigate the effects of light intensity on aggressive encounters and social stability in groups of adult male Nile tilapia, Oreochromis niloticus (Linnaeus, 1758). The study compared the behavior observed under low (280.75 ± 50.60 lx) and high (1394.14 ± 520.32 lx) light intensities, with 12 replicates for each treatment. Adult fish were isolated in 36-L aquaria for 96 hours, and three males were grouped for 11 days in 140-L aquaria. Agonistic behavior was video-recorded (10 min/day) on the 3rd, 5th, 7th, and 9th day to quantify aggressive interactions and social stability. There was an effect of light intensity and day of observation on the total number of agonistic behaviors performed by the fish group. Besides, increased frequency of aggressive interactions (the sum of the four sessions) by the alpha, beta and gamma fish occurred at the higher light intensity. The dominance ranks of the fish remained unchanged across the observation sessions under both the low and high light intensities. We concluded that enhanced light intensity has a cumulative effect that increases the aggressiveness of the Nile tilapia but that this effect is not sufficiently strong to destabilize the social hierarchy.(AU)