Syntopic species with similar anatomic configuration may face strong competition for trophic resources, thus relying on developed mechanisms to ensure coexistence. The present study investigated the influence of body size on trophic interactions between juveniles of two closely related fish species at three sandy beaches in south-eastern Brazil. A total of 150 fish were sampled, where 103 were identified as Trachinotus carolinus (mean ± SE: weight = 9 g ± 1.13) and 47 as Trachinotus goodei (weight = 46.7 g ± 3.34). A significant size-difference between juvenile Trachinotus was detected by a null-model analysis (P = 0.04), with T. carolinus (TL = 79.6 mm ± 2.4) presenting a smaller body size than T. goodei (TL = 147.7 mm ± 4.2). The main prey items consumed by T. carolinus were Perna perna (IAi = 0.76) and Emerita brasiliensis (IAi = 0.18), whereas the latter was the major T. goodei dietary prey (IAi = 0.71). Both prey were correlated with larger-sized juveniles of each pompano species, whereas smaller fish shared non-preferred trophic items. Such opportunistic behaviour of smaller juveniles may account for the dietary overlap detected between the Trachinotus species (P = 0.09). Size-related dietary partitioning was observed for the largest T. goodei juveniles, which displayed only a slight overlap with T. carolinus, and between juveniles belonging to the small and medium size groups of each pompano species. Therefore, food partitioning related to pompano body size seems to be especially important for the smallest juveniles, as they present the highest vacuity (particularly T. carolinus) in the sampled beaches, suggesting that these individuals are under intra- and interspecific competitive pressure, which may affect local coexistence.

中文翻译：

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大小对两种同位鲫鱼幼鱼营养相互作用的影响

具有相似解剖结构的同位物种可能面临对营养资源的激烈竞争，因此依靠发达的机制来确保共存。本研究调查了体型对巴西东南部三个沙滩​​上两种密切相关的鱼类幼鱼之间营养相互作用的影响。共取样 150 条鱼，其中 103 条被确定为卡罗来纳鲽（平均值 ± SE：重量 = 9 g ± 1.13）和 47鲽鱼（重量 = 46.7 克 ± 3.34）。青少年之间的显着大小差异鲫鱼通过空模型分析检测到（磷= 0.04），与卡罗来纳(TL = 79.6 mm ± 2.4) 呈现出比T.goodei（TL = 147.7 毫米 ± 4.2）。消耗的主要猎物卡罗来纳是珍珠贝(IAi = 0.76) 和Emerita brasiliensis(IAi = 0.18)，而后者是主要的T.goodei饮食猎物（IAi = 0.71）。两种猎物都与每个鲳鱼种类的较大幼鱼相关，而较小的鱼则共享非首选的营养项目。体型较小的幼鱼的这种机会主义行为可能解释了它们之间检测到的饮食重叠鲫鱼物种 （磷= 0.09)。最大的观察到与大小相关的饮食分配T.goodei青少年，仅显示与卡罗来纳，以及属于每个鲳鱼种类的中小型群体的幼鱼之间。因此，与鲳鲳体型相关的食物分配似乎对最小的幼鱼尤为重要，因为它们的真空度最高（尤其是卡罗来纳) 在采样的海滩中，表明这些个体处于种内和种间的竞争压力下，这可能会影响当地的共存。