Abstract
Aspects of the reproductive biology of Astyanax janeiroensis in the Ubatiba river in Maricá, RJ, Brazil were evaluated in order to ascertain whether the strategy adopted by the species is causally related to environmental variables. Specimens were collected on a monthly basis from October 1994 to September 1995, through electrofishing. The Sex ratio was not significantly different from the expected frequency of 1:1 (G = 1.29; p > 0.50); nonetheless, considering three standard length classes, significantly larger numbers of females were recorded for the higher SL class (G = 11.07; p < 0.01). Size at first maturation showed no significant differences between sexes. Length-weight ratio analyses showed negative allometry for males and isometry, for females. Length structure was significantly different between sexes, suggesting that females are larger than males (D = 0.027, p < 0.01). Reproductive specimens were recorded during nine months of the annual cycle. Seasonal variations of reproductive specimens belonging to two different standard length classes displayed an asynchronous behavior, with larger specimens having a longer reproductive period and smaller ones reproducing for fewer months during the annual cycle. High values of fecundity (F), varying from 3169 to 18714 oocytes, were recorded for fish of 9.1 and 10.2 cm lengths, respectively. The correlation between weight and number of oocytes/unit of weight was positive, indicating that larger specimens produced more eggs.
Highlights
Following the heretofore narrow perspective of fish life history (Matthews, 1998), knowledge of some reproductive traits such as sexual dimorphism, egg size, fecundity and spawning time are fundamental to understand how these traits should be adapted to maximize reproductive success in a particular environment
Despite the high plasticity of many life history traits, important constraints imposed by fundamental morphology or phylogeny are observed among different fish species
Reproductive strategies of stream dwelling fish in Brazilian coastal streams have been reported at various times, with the work of Garutti (1983, 1988), Menezes & Caramaschi (1994), Soares-Porto (1991), Aranha & Caramaschi (1999), Mazzoni & Petito (1999) and Mazzoni et al (2002a) ranking among the most important
Summary
Following the heretofore narrow perspective of fish life history (Matthews, 1998), knowledge of some reproductive traits such as sexual dimorphism, egg size, fecundity and spawning time are fundamental to understand how these traits should be adapted to maximize reproductive success in a particular environment. Despite the high plasticity of many life history traits, important constraints imposed by fundamental morphology or phylogeny are observed among different fish species. Reproductive strategies of stream dwelling fish in Brazilian coastal streams have been reported at various times, with the work of Garutti (1983, 1988), Menezes & Caramaschi (1994), Soares-Porto (1991), Aranha & Caramaschi (1999), Mazzoni & Petito (1999) and Mazzoni et al (2002a) ranking among the most important. The traits analyzed here include size structure, length to weight ratio, size at first reproduction, fecundity, sex ratio and reproductive season
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