Round gobies (Neogobius melanostomus) from the upper St. Lawrence River (USLR) have an abundance of some of the largest individuals recorded from the Great Lakes (>230-mm total-length). We found a distinct separation in diet and isotopic signatures (δ¹⁵N and δ¹³C) between round goby classified as small (≤130-mm; n = 63) and large (>130-mm total-length; n = 75) from USLR coastal bays. At small sizes, round gobies had variable diets indicative of generalist and opportunistic feeding on native and non-indigenous benthic prey. Between 100 and 130-mm total-length, signatures of assimilated carbon (δ¹³C) indicated a directed shift towards a dreissenid-centric diet and once larger than 130-mm total-length, round gobies appeared to feed proportionally more on dreissenid mussels. We also found that large round gobies fed proportionally more on Hydrobiidae than small round gobies. A weak negative relationship between δ¹⁵N (indicative of trophic position) and round gobies total length resulted where smaller round gobies had slightly higher δ¹⁵N values than larger conspecifics. Round gobies larger than 180-mm total-length were common in nearshore habitats (≤2-m) during the spring, and dreissenid mussels and Hydrobiidae were the most frequently encountered prey. Our results demonstrate elevated reliance on dreissenids as round goby increased body size, but the diversity of prey suggest more complex trophodynamic pathways associated with coastal bay habitats.

来自圣劳伦斯河上游 (USLR) 的圆形虾虎鱼 ( Neogobius melanostomus ) 拥有大量记录自五大湖 (>230 毫米总长度) 的最大个体。我们发现在被归类为小型（≤130 毫米；n = 63）和大型（>130 毫米总长度；n = 75）的圆形虾虎鱼之间，饮食和同位素特征（δ ¹⁵ N 和 δ ¹³ C）存在明显区别从 USLR 沿海海湾。在体型较小的情况下，圆形虾虎鱼有不同的饮食，表明以本地和非本地底栖猎物为食。总长度在 100 到 130 毫米之间，同化碳的特征 (δ ¹³C) 表明直接转向以德莱森为中心的饮食，一旦总长度超过 130 毫米，圆形虾虎鱼似乎更多地以德莱森贻贝为食。我们还发现饲喂，大型圆虾虎鱼比例更多Hydrobiidae比小圆虾虎鱼。δ ¹⁵ N（营养位置的指示）和圆形虾虎鱼总长度之间存在弱负相关，导致较小的圆形虾虎鱼的δ ¹⁵ N 值略高于较大的同种虾。春季，近岸生境（≤2 米）常见总长大于 180 毫米的圆形虾虎鱼，以及德莱森贻贝和海螺科是最常遇到的猎物。我们的研究结果表明，随着圆形虾虎鱼的体型增加，对德莱森鱼的依赖程度提高，但猎物的多样性表明与沿海海湾栖息地相关的营养动力学途径更为复杂。