Effects of Trophic Poisoning with Methylmercury on the Appetitive Elements of the Agonistic Sequence in Fighting-Fish (Betta Splendens)

Abstract

The aggressive display in Betta splendens is particularly prominent, and vital to its adaptation to the environment. Methylmercury is an organic variation of Hg that presents particularly pronounced neuro-behavioral effects. The present experiments aim to test the effect of acute and chronic poisoning with methylmercury on the display in Bettas. The animals were poisoned by trophic means in both experiments (16 ug/kg in acute poisoning; 16 ug/kg/day for chronic poisoning), and tested in agonistic pairs. The total frequency of the display was recorded, analyzing the topography of the agonistic response. The methylmercury seems to present a dose-and detoxification-dependent effect on these responses, with a more pronounced effect on motivity in acute poisoning and on emotionality in the chronic poisoning. It is possible that this effect could be mediated by alteration in the mono-amino-oxidase systems. Keywords: methylmercury, aggression, emotional behavior, Betta splendensEl despliegue agresivo en la Betta splendens es especialmente prominente y es vital para su adaptación al medio ambiente. Metil-mercurio es una variación orgánica de Hg que presenta efectos neuro-conductuales especialmente pronunciados. Los experimentos actuales intentan poner aprueba el efecto de envenenamiento agudo y crónico con metil-mercurio sobre el despliegue en Bettas. Los animales fueron envenenados tróficamente en ambos experimentos (16 ug/kg e el envenenamiento agudo) y probados en parejas agonistas. Se registró la frecuencia total del despliegue, analizando la topografía de la respuesta agonista. El metil-mercurio parece presentar un efecto dependiente de la dosis y de la detoxificación sobre estas respuestas, con un efecto más pronunciado sobre la motilidad en el envenenamiento agudo y sobre la emotividad en el envenenamiento crónico. Posiblemente, este efecto podría mediarse por la alteración en los sistemas de mono-amino-oxidasa.

Effects of Mercury Chloride (HgCl2) on Betta Splendens Aggressive Display

“…The display response should be elicited by placing a member of the same species in the same (or another) aquarium, or by the use of a mirror or subject model (Meliska et al, 1980). The vigor with which animals present their display, defined by the duration and frequency of the demonstration, is a reliable predictor of the animal's performance in a real combat situation (Evans, 1985) and in situations in which dominance is established (Gouveia et al, 2007).…”

“…The aggressive/reproductive display of the Siamese fighting fish (Betta splendens), is a species-specific agonistic sequence that may be separated into appetitive, mating, and post-mating components (Klein, Figler, & Peeke, 1976). In the case of Betta splendens, the appetitive components that correspond to the display have been extensively studied (Gouveia et al, 2007). These appetitive components are characterized by specific behaviors, such as saturation of body color, erection of the opercles or gill cover, orientation and movement characteristics (Simpson, 1968).…”

“…An alteration in one of the appetitive components predictably alters the mating components (Klein et al, 1976;Bronstein, 1985). The display is very prominent and Bronstein (1980Bronstein ( , 1981Bronstein ( , 1982 suggested that this is an agonistic and reproductive strategy typical of many teleosts using external fertilization in relation to the body of the female of the species (see also Simpson, 1968;Gouveia et al, 2007).…”

“…The present study used the same ethogram as that utilized by Gouveia et al (2007), which presents 12 behavioral patterns of the Siamese fighting fish (see table 1). These patterns were used as a measure for evaluating behavioral changes caused by mercury chloride.…”

“…However, studies with methylmercury (MeHg) have shown that poisoning causes behavioral changes that correspond in topography to the fish responses to predators (Smith & Weis, 1997), feeding behavior (Fjeld, Haugen, & Vøllestad, 1998), as well as the anxiety responses of rats and fishes of the Danio rerio species (Gouveia et al, 2003). There are also effects on aggression, motility and emotionality, an effect that could be caused by alterations in the monoamino-oxidase systems (Gouveia, Oliveira, Romão, Brito, & Ventura, 2007).…”