The Neotropical region is highly diverse in fresh water teleost fishes and extends through vast regions of South America. The genus Astyanax comprises small fish found in the tributaries and ditches of the great Brazilian basins, such as the Paraná and São Francisco Rivers. This group has been ostensibly studied from a chromosomal and molecular point of view but is still involved in problems of phylogenetic location, justifying its position incertae sedis, while having a wide diversity of forms and habitats. Our study counted on the analysis of body shape variations in seven species of the genus Astyanax and in the bimaculatus, fasciatus, and scabripinnis complexes using geometric morphometrics. We obtained images of individuals from different localities in the Paraná and São Francisco River basins, delineated two-dimensional anatomical landmarks that we then subjected to the generalized Procrustes analysis, and subsequent ordination by principal component analysis and canonical variate analysis. The results showed variation between two large groups, related mainly to variations in body height, indicating the probable existence of different evolutionarily significant units morphologically shaped by the pressure of the environment with what may be incipient speciation.

新热带地区的淡水硬骨鱼种类繁多，并延伸到南美广大地区。Astyanax属包括在巴西大流域（如Paraná和SãoFrancisco Rivers）的支流和沟中发现的小鱼。表面上已经从染色体和分子的角度研究了该组，但仍涉及系统发生位置问题，证明其在不安全的位置是合理的，同时具有广泛的形式和栖息地。我们的研究在七个属种的算的上体形变化的分析Astyanax并在双斑，暗纹东方鲀，并scabripinnis使用几何形态计量学的复合体。我们获得了来自巴拉那州和圣弗朗西斯科河流域不同地点的个体的图像，描绘了二维解剖标志，然后进行了广义Procrustes分析，然后通过主成分分析和规范变量分析进行了排序。结果表明，两个大型群体之间存在差异，主要与身高变化有关，这表明可能存在着不同的具有进化意义的单位，这些单位在形态上受环境压力的影响而形成，可能是初期物种形成。