Body shape is a morphological attribute that frequently changes as organisms adapt to environmental fluctuations and optimize the use of available resources. In fish whose distribution includes estuarine and riverine environments, it is common to observe changes in body shape that are related to maneuverability and speed of movement in response to temporal and spatial variation in water flow. Here, through geometric morphometric and linear morphometric analysis, the intraspecific morphological variation of the cichlids Amphilophus trimaculatus, Astatheros macracanthus, and Mayaheros beani was evaluated to determine if there are repeated patterns of variation in body shape associated with estuarine and riverine environments. The three species showed the same trend of morphological variation; in the estuaries, the specimens were generally deeper and robust, with a long head and short caudal peduncle, while river specimens had shallowed and fusiform bodies with a short head and long caudal peduncle. The magnitude of the changes was not the same in the three species, as M. beani showed greater differentiation, and some morphological measures showed changes in opposite directions between the species. These findings indicate that the environment occupied by the species is an important factor in the differentiation of body shape, probably due to water flow, although other factors may determine the magnitude and direction of change in some morphological traits.

体形是一种形态属性，随着生物体适应环境波动和优化可用资源的利用而经常发生变化。在分布于河口和河流环境的鱼类中，通常会观察到与响应水流的时间和空间变化的机动性和运动速度相关的体形变化。在这里，通过几何形态测量和线性形态测量分析，评估了慈鲷Amphilophus trimaculatus、Astatheros macracanthus和Mayaheros beani的种内形态变异，以确定是否存在与河口和河流环境相关的体形变异的重复模式。三个物种的形态变异趋势一致；在河口，标本一般较深、粗壮，头部长，尾柄短；而河流标本则体浅，呈纺锤形，头部短，尾柄长。三个物种的变化幅度并不相同，因为M. beani显示出更大的分化，并且一些形态学测量显示物种之间的变化方向相反。这些发现表明，物种所处的环境是体形分化的重要因素，可能是由于水流所致，尽管其他因素可能决定某些形态特征变化的幅度和方向。