Effects of methylmercury on electric organ discharges in the weak electric fish Gymnotus sylvius

Methylmercury (MeHg) is present in the environment because of natural and anthropogenic causes. MeHg can reach the central nervous system (CNS) and cause neurological damage in humans and animals. Electric organ discharges (EODs) in the weak electric fish Gymnotus sylvius are produced by the electric organ and modulated by the CNS. These discharges are used for electrolocation and communication. The purpose of the present study was to investigate the effects of dietary MeHg exposure on EOD rate in G. sylvius. An oscilloscope was used to record the EOD rate. Two treatments were investigated: chronic MeHg administration (4 µg/kg MeHg every 2 days, with a total of nine dietary exposures to MeHg) and acute MeHg administration (a single dose of 20 µg/kg MeHg). The control data for both treatments were collected every 2 days for 18 days, with a total of nine sessions (day 1 until day 18). Data of fish exposed to MeHg were collected every 2 days, totaling nine sessions (day 19 until day 36). Chronic treatment significantly increased the EOD rate in G. sylvius (p < .05), especially with the final treatment (day 32 until day 36). Acute treatment resulted in an initial increase in the EOD rate, which was maintained midway through the experiment (day 26 until day 30; p < .05). The present study provides the first insights into the effects of MeHg on EODs in weak electric fish. The EOD rate is a novel response of the fish to MeHg administration.(AU)

Effects of methylmercury on electric organ discharges in the weak electric fish Gymnotus sylvius

Methylmercury (MeHg) is present in the environment because of natural and anthropogenic causes. MeHg can reach the central nervous system (CNS) and cause neurological damage in humans and animals. Electric organ discharges (EODs) in the weak electric fish Gymnotus sylvius are produced by the electric organ and modulated by the CNS. These discharges are used for electrolocation and communication. The purpose of the present study was to investigate the effects of dietary MeHg exposure on EOD rate in G. sylvius. An oscilloscope was used to record the EOD rate. Two treatments were investigated: chronic MeHg administration (4 µg/kg MeHg every 2 days, with a total of nine dietary exposures to MeHg) and acute MeHg administration (a single dose of 20 µg/kg MeHg). The control data for both treatments were collected every 2 days for 18 days, with a total of nine sessions (day 1 until day 18). Data of fish exposed to MeHg were collected every 2 days, totaling nine sessions (day 19 until day 36). Chronic treatment significantly increased the EOD rate in G. sylvius (p < .05), especially with the final treatment (day 32 until day 36). Acute treatment resulted in an initial increase in the EOD rate, which was maintained midway through the experiment (day 26 until day 30; p < .05). The present study provides the first insights into the effects of MeHg on EODs in weak electric fish. The EOD rate is a novel response of the fish to MeHg administration.

Efeitos do observador sobre o comportamento de sagüis (Callithrix jacchus) não habituados de vida livre / Observer effects on the behavior of non-habituated wild living marmosets (Callithrix jacchus)

In order to assess the influence of the presence of a human observer on the behavior of wild, non-habituated common marmosets (Callithrix jacchus), a group of marmosets was exposed to sessions of observation in which observers were visible and in which they hided into a blind. Results indicated that typical defensive reactions such as alarm calls and stares at observers were reduced when observations were made from inside the blind. There was no significant differences in other parameters such as foraging/social contact calls, minimal distance from observer and time duration of sessions. Both major and minor modifications in normal behavior of free living animals may thus arise from the conditons of observation and should be taken into account.(AU)

Para avaliar o impacto da presença de um observador humano sob o comportamento de sagüis silvestres (Callithrix jacchus), o comportamento de um grupo desses animais foi observado em sessões conduzidas, aleatoriamente por observadores visíveis e dentro de uma barraca camuflada. Verificou-se que as reações defensivas típicas, como chamadas de alarme e olhares fixos aos observadores, foram reduzidas no caso das observações feitas dentro da barraca, não havendo diferenças significativas em parâmetros como contato social, forrageamento, distância mínima do observador e a duração do tempo das sessões de observações. As condições de observação podem exercer modificações no comportamento de animais em estudos naturalísticos e deveriam ser levadas em conta.(AU)