Life history traits of the glass knifefish Eigenmannia desantanai (Gymnotiformes: Sternopygidae) in the Southern Pantanal, Brazil

Características de história de vida da tuvira Eigenmannia desantanai (Gymnotiformes: Sternopygidae) no Pantanal Sul, Brasil

Abstracts

Abstract 

Aim  This study investigated life-history traits of Eigenmannia desantanai in the southern Pantanal floodplain.

Methods  Fish were collected beneath stands of aquatic macrophytes using seine nets and rectangular sieves with a 2 mm mesh size in the Paraguay and Amonguijá rivers between February 2009 and January 2011.

Results  A total of 484 individuals were sampled, including 351 females, 113 males, and 20 individuals of undetermined sex. Females predominated in the population (3.1:1), and no significant differences were observed in total weight or standard length between sexes. Both sexes exhibited negative allometric growth. Females reached sexual maturity at an estimated standard length of 63.06 mm, and males at 59.58 mm. Mean absolute fecundity was 305.3 oocytes (mean relative fecundity = 0.17), with no significant correlation with female body weight or standard length. The frequency distribution of oocyte diameter indicated batch spawning. Females showed a prolonged reproductive period, with two peaks in gonadosomatic index (GSI) values: the first from January to April, and the second including June, August, and September. GSI was correlated with river level and temperature. In contrast, males reproduced throughout the year, with no influence from environmental variables.

Conclusions  The results indicate that E. desantanai responds to immediate environmental conditions and demonstrates high reproductive investment through a prolonged breeding period. Reproductive peaks occurred during the hydrological phases of rising waters and flood, associated with high or increasing temperatures. Additionally, the species exhibits low fecundity, batch spawning, and an extended reproductive period, characterizing it as an equilibrium strategist.

Keywords:
reproductive biology; population biology; small fish; Paraguay river; tuvira