Estuarine habitats are major nurseries for the European flounder Platichthys flesus, with different year classes sharing food and space resources. Hence, an understanding of feeding strategies that optimize resource use and maintain carrying capacity is fundamental for sustainable and successful ecosystem management. The main feeding areas of juvenile European flounder (including 0-group and 1-group age classes) in the Lima estuary (northern Portugal) nursery ground were investigated by integrating stomach content analyses with stable isotopic values (δ13C and δ15N) and fish condition indices (Fulton K and RNA:DNA ratio). The 0-group flounder that were associated with the upstream section of the estuary presented the lowest δ13C value (−25.58 ± 1.86‰), while 1-group flounder exhibited a higher δ13C value (−22.59 ± 2.51‰), indicating use of the more saline areas of the estuary (lower and middle sections). The two age groups did not differ in terms of δ15N (0-group: 13.93 ± 0.29‰; 1-group: 13.50 ± 0.96‰), indicating similar trophic levels. The low salinity upper estuary was the main feeding area of 0-group flounder (74%), while 1-group flounder fed along the estuary both upstream (52%) and downstream (48%). Juvenile flounder showed high individual condition based on the Fulton K index (0-group: 1.05 ± 0.08; 1-group: 1.07 ± 0.05) and RNA:DNA (0-group: 1.70 ± 0.70; 1-group: 1.41 ± 0.47). These indices deal with fish health, and hence indicate nursery habitat quality. It is concluded that in this temperate nursery habitat, different feeding strategies sustained the condition of the European flounder juveniles, compared with other flounder populations.

中文翻译：

---

幼年欧洲比目鱼苗圃栖息地的摄食策略和身体状况

河口栖息地是欧洲比目鱼的主要栖息地鹧鸪，不同年级的学生共享食物和空间资源。因此，了解优化资源利用和保持承载能力的饲养策略是可持续和成功的生态系统管理的基础。通过将胃含量分析与稳定同位素值（δ13C和δ15N）和鱼类状况指数（富尔顿 K 和 RNA：DNA 比率）。与河口上游段相关的0组比目鱼的δ最低13C值（-25.58±1.86‰），而1组比目鱼表现出更高的δ13C 值（-22.59 ± 2.51‰），表明使用河口含盐量较高的区域（下段和中段）。两个年龄组在 δ 方面没有差异15N（0组：13.93±0.29‰；1组：13.50±0.96‰），表明营养水平相似。低盐度的上河口是0组比目鱼（74％）的主要觅食区，而1组比目鱼沿河口上游（52％）和下游（48％）取食。根据 Fulton K 指数（0 组：1.05 ± 0.08；1 组：1.07 ± 0.05）和 RNA：DNA（0 组：1.70 ± 0.70；1 组：1.41 ± 0.47），幼比目鱼表现出较高的个体状况. 这些指数涉及鱼类健康，因此表明了育苗栖息地的质量。得出的结论是，在这个温带育苗栖息地，与其他比目鱼种群相比，不同的喂养策略维持了欧洲比目鱼幼鱼的状况。