Reproductive biology of a population of Gymnotus aff.carapo (Teleostei: Gymnotidae) from southern Brazil

Abstract

The reproductive period and its relation with somatic and abiotic factors, the relative and absolute fecundity, spawning type, length of first maturation and sex ratio is describe for Gymnotus aff. carapo from a small lake at Itapuã State Park, Rio Grande do Sul, Brazil. Gymnotus aff. carapo presents a relatively long reproductive cycle extending from November/2003 to March/ 2004. Decreases in water conductivity and increases in dissolved oxygen are correlated with increased gonadal development in males. In females, seasonal increases in temperature and photoperiod and decreases in dissolved oxygen are correlated with increased gonadal development. The mean absolute fecundity was 915.3 oocytes, and mean relative fecundity 0.20 oocytes/ mg body weight. Egg size distributions indicate multiple spawning. The size of first maturation was 141 mm in females and 146 mm in males. The sex ratio was 1:1, with a male bias only in smaller size classes.São descritos o período reprodutivo e a relação deste com fatores bióticos e abióticos, a fecundidade absoluta e relativa, o tipo de desova, comprimento de primeira maturação e proporção sexual de Gymnotus aff. carapo de um pequeno lago no Parque Estadual de Itapuã, Rio Grande do Sul, Brazil. A espécie apresentou um período reprodutivo relativamente longo, de novembro de 2003 até março de 2004. Houve correlação significativamente positiva entre o IGS dos machos e o oxigênio dissolvido e negativa em relação à condutividade. O IGS das fêmeas se correlacionou positivamente com a temperatura e fotoperíodo, e negativamente com o oxigênio dissolvido. A fecundidade absoluta média foi de 915,3 ovócitos e a fecundidade relativa média foi de 0,20 ovócitos por miligrama de peso da fêmea. A desova foi considerada parcelada e o tamanho de primeira maturação gonadal foi de 141 mm para fêmeas e 146 mm para machos. A proporção sexual no período amostrado foi de 1:1, sendo que somente na menor classe de comprimento houve maior abundância dos machos.

Structure of the littoral fish assemblage in an impounded tributary: the effects of macrophytes presence (subtropical region, Brazil)

“…A negative correlation to some environmental variables (DO and pH) was observed only for the abundance of G. carapo, which suggests that this species can tolerate adverse physicochemical conditions. This tolerance was also observed by Cognato and Fialho (2006), who found that females of this species presented an increase in gonadal development correlated to a decrease in dissolved oxygen levels.…”

“…This positive effect of macrophyte cover on the abundance of G. carapo may be related to the biological and ecological aspects of this species. G. carapo is a multiple spawner species which exhibits territorial, parental care and building nests behavior (Campos-da-Paz, 2003;Cognato and Fialho, 2006). Besides that, it has a carnivorous feeding habit with a preference for small aquatic animals (Albert and Crampton, 2003), a lateral compressed body and a superior mouth (Campos-da-Paz, 2003).…”

Reproductive biology of the Neotropical electric fish Brachyhypopomus draco (Teleostei: Hypopomidae) from southern Brazil

“…Studies at Parque Estadual de Itapuã concerning gymnotiform species have established reproductive periods occurring from October to February for Eigenmannia trilineata (Giora & Fialho, 2009) and from November to March for Gymnotus aff. carapo (Cognato & Fialho, 2006). With this mind, the low rainfall rates and water depth observed during the months of January through April of the year studied might have induced the regression of male and female gonads and might have determined the anticipation of the end of the B. draco population breeding season.…”

“…Caudal filaments depth Level 1 = from 0 to 1.5%; Level 2 = from 1.51% to 2.5%; Level 3 = from 2.51% to 3.50%. (Silva et al, 1999;Ardanaz et al, 2001;Silva et al, 2002;Quintana et al, 2004), in photoperiod (Giora & Fialho, 2009) or in both temperature and photoperiod (Silva et al, 2003;Cognato & Fialho, 2006). For the B. draco population from lagoa Verde, the male reproductive cycle showed a positive relation with temperature, but no relation was found for photoperiod.…”

“…For gymnotiform species, few data concerning reproductive aspects are available (Kirschbaum, 1979;Barbieri & Barbieri, 1982, 1983a, 1983b, 1984a, 1984bHagedorn, 1988;Assunção & Schwassmann, 1995;Kirschbaum & Schugardt, 2002;Silva et al, 2003;Quintana et al, 2004). In southern Brazil, studies on the reproductive biology of gymnotiform species have been undertaken by Cognato & Fialho (2006) on Gymnotus aff. carapo, by Giora & Fialho (2009) concerning Eigenmannia trilineata, and by Giora (2008) concerning two Brachyhypopomus species, all in the protected area of Parque Estadual de Itapuã.…”