A new and improved electric fish finder with resources for printed circuit board fabrication

We describe the circuit design, construction, and operation of a field-portable electric fish finder (an AC-coupled wide-band differential bio-amplifier with loudspeaker output). This device permits detection and monitoring of the electric organ discharges generated by neotropical gymnotiform fishes (as well as the mormyroid fishes of tropical Africa). Our design is modified from earlier versions to optimize detection performance and stability over a wider range of ambient water conductivity, including under conditions of extremely low conductivity (< ca. 10 μScm-1). Our new electric fish finder design also incorporates complete waterproofing and longer battery autonomy. We provide Gerber and Eagle files made with the electronic design automation software 'Autodesk Eagle' to allow researchers to order printed circuit boards directly from commercial manufacturers.(AU)

Nós descrevemos o projeto de circuitos eletrônicos e as instrucões para a construção e uso de um detector de peixes elétricos portátil (bio-amplificador diferencial de banda-larga com acoplamento AC). Este aparelho permite a detecção e o monitoramento das descargas de órgãos elétricos gerados por peixes neotropicais da ordem Gymnotiformes (assim como dos peixes mormirídeos da África Tropical). Nosso projeto é modificado a partir de versões anteriores para otimizar o desempenho e a estabilidade sob uma faixa de condutividades ambientais mais ampla, incluindo condições de condutividade extremamente baixa (< ca. 10 μScm-1). Nosso detector de peixes elétricos novo também foi otimizado a fim de proporcionar impermeabilização completa e vida longa para as baterias. Nós fornecemos arquivos 'Gerber' e 'Eagle' preparados com o software de automação de projeto eletrônico 'Autodesk Eagle' para permitir aos pesquisadores a possibilidade de efetuar encomendas de nossa placa de circuito impresso direitamente das empresas de fabricação.(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.

Brachyhypopomus draco, a new sexually dimorphic species of Neotropical electric fish from southern South America (Gymnotiformes: Hypopomidae)

Brachyhypopomus draco, new species, is described from central, southern and coastal regions of Rio Grande do Sul state, Brazil, and Uruguay. It is diagnosed from congeners by, among other characters, the shape of the distal portion of the caudal filament in mature males, which during the reproductive period forms a distinct paddle shape structure.

Brachyhypopomus draco, espécie nova, é descrita para as regiões central, sul e costeira do estado do Rio Grande do Sul, Brasil, e Uruguai. Ela é diagnosticada de seus congêneres, entre outros caracteres, pela porção final do filamento caudal de machos maduros, que adquire a forma de um remo durante o período reprodutivo.

Design and construction of an Electric Fish Finder

We provide notes on the design and construction of an Electric Fish Finder - a portable differential amplifier for detecting the electrostatic fields of gymnotiform knifefishes. The device can be adapted to locate electric fishes in any kind of aquatic environment. It is rugged, water resistant, and powered by alkaline batteries. This contribution is part of a series of technical papers designed to encourage students of neotropical ichthyology to explore the ecology, systematics, and electric signaling of gymnotiform fishes

Nós fornecemos o esquema e as instruções para a construção de um Detector de Peixes Elétricos - um amplificador portátil de banda larga utilizado para detectar os campos elétricos de peixes gymnotiformes. Este aparelho pode ser adaptado para encontrar peixes elétricos em diversos ambientes aquáticos. É resistente, à prova d'água e energizado por baterias alcalinas. Esta contribuição faz parte de uma série de artigos técnicos que pretende encorajar estudantes de ictiologia neotropical a explorar a ecologia, sistemática e comunicação elétrica de peixes gymnotiformes