Abstract. Technological development for Gymnotus sp. farming is relevant because this species has a socio- economic impact in South American regions where sport fishing is an important activity. Although Gymnotus sp. breeds in captivity, fry survival in ponds can be unacceptable for culture systems. The objective of this work was to test the response to hormonal induction of Gymnotus sp. with carp pituitary extract (CPE) and gonadotrophin-releasing hormone (GnRH) in relation to different male and female reproductive parameters. CPE treatment specimens were stripped 12 and 20 hours after the triggering dosage, and GnRH treatment specimens were stripped 10 and 12 hours after hormonal application. We could obtain positive results using CPE with a short capture-induction interval (C-II) with broodstock in mature stages of gonadal development. Percentage of oocytes with peripheral germinal vesicle (%OPGV) and oocyte diameter showed significant differences between groups treated with CPE. Oocytes could be successfully extracted from two females treated with CPE and stripped 12 hours after the last dosage. Semen was only extracted from males treated with CPE. GnRH stimulation did not give positive results because gametes could not be extracted with different doses and C-II used. This work is the first description of semen quality parameters in Gymnotus sp. Future works should focus on combining hormonal induction strategies with CPE and the management of environmental variables.

Resumen El desarrollo tecnológico para el cultivo de Gymnotus sp. es relevante porque este género tiene un impacto socioeconómico en regiones sudamericanas donde la pesca deportiva es una actividad importante. Aunque Gymnotus sp. se reproduce en cautiverio, la supervivencia de los alevines en los estanques puede ser insuficiente para un sistema de cultivo. El objetivo de este trabajo fue evaluar la respuesta de diferentes parámetros reproductivos a la inducción hormonal en Gymnotus sp. con extracto bruto de hipófisis de carpa (EBH) y hormona liberadora de gonadotrofinas (GnRH). Las muestras de gametos del tratamiento con EBH se extrajeron 12 y 20 horas después de la dosis desencadenante, las muestras del tratamiento con GnRH se extrajeron 10 y 12 horas después de la aplicación hormonal. El porcentaje de ovocitos con vesícula germinal periférica (%OVGP) y el diámetro de los ovocitos mostraron diferencias significativas entre grupos tratados con EBH con un intervalo captura-inducción (IC-I) de corta duración, con reproductores en etapas avanzadas de desarrollo gonadal. Se pudieron extraer ovocitos con éxito a dos hembras inducidas con EBH, 12 horas después de la dosis desencadenante y, además, se extrajo semen sólo de los machos inducidos con EBH. La estimulación con GnRH no dio resultados positivos en las diferentes dosis e IC-I utilizados, dado que no se pudieron extraer gametos. Este trabajo es la primera descripción de los parámetros de calidad del semen en Gymnotus sp. Futuras líneas de trabajo deberán centrarse en el manejo de variables ambientales para establecer una estrategia de reproducción que se pueda utilizar a nivel productivo.

Trinta e seis espécimens de Schizodon nasutus (Anostomidae-Characiformes) do médio Paraná (Posadas, Argentina) foram analisados citogeneticamente. O cariótipo encontrado foi semelhante aos descritos para esta espécie na literatura. A técnica de bandamento C mostrou um rico padrão heterocromático em relação a outras espécies de Anostomidae. As NORs localizaram-se em um par cromossômico em posição terminal e mostraram um acentuado heteromorfismo de tamanho. Um microcromossomo foi observado com freqüência de cerca de 20% na amostra estudada. Este elemento adicional era puntiforme, bandamento C negativo e constante em todas as placas metafásicas dos sete portadores. O presente estudo é o primeiro com abordagem cariotípica em Schizodon nasutus da Argentina e a primeira descrição de microcromossomo em Anostomidae

Thirty-six specimens of Schizodon nasutus (Anostomidae-Characiformes) from the middle Paraná River (Posadas, Argentina) were analyzed cytogenetically. The karyotype of this species was similar to those described for this species in the literature. C-banding technique showed a rich heterochromatic pattern relative to other Anostomidae species. The NORs were located on one chromosome pair in terminal position and showed a very marked size heteromorphism. A microchromosome was observed with a frequency of about 20% in the sample studied. This additional element was punctiform, negative C-band, and constant in all metaphase plates of the seven carriers. The present study is the first karyotypic approach to Schizodon nasutus from Argentina and the first description of microchromosome in Anostomidae