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

Diego De Paula Cognato,Clarice Bernhardt Fialho

doi:10.1590/s1679-62252006000300005

Diego De Paula Cognato, Clarice Bernhardt Fialho

Open Access

https://doi.org/10.1590/s1679-62252006000300005

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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.

Highlights

Electric fishes of the order Gymnotiformes, known in Brazil as “sarapós” and “tuviras”, have the remarkable ability to generate and detect electric fields (Bennett, 1971)
We investigate the reproductive biology of a population from a small lake in Itapuã State Park, Rio Grande do Sul, Brazil
Two species of gymnotiforms occur in the lagoa Verde, G. aff. carapo and an undescribed species of Brachyhypopomus

Summary

Introduction

Electric fishes of the order Gymnotiformes, known in Brazil as “sarapós” and “tuviras”, have the remarkable ability to generate and detect electric fields (Bennett, 1971) This ability enable these fishes explore their habitat, communicate with conspecific and perceive objects and other creatures in the environment. Gymnotus has the widest geographical range of all gymnotiform genera, occurring throughout lowland South and Central America from río Salado in the Argentinean Pampas to the río San Nicolas, Mexico. It occurs in the Caribbean island of Trinidad. Gymnotus species are aggressive nocturnal predators of fishes and other small aquatic animals (Albert & Crampton, 2003). Kirschbaum & Wieczorec (2002), Kirschbaum & Schugardt (2003) and Crampton & Hopkins (2005), describe parental care behavior in Gymnotus species

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