Non-native fish invasions threaten native fauna and ecosystem functioning, not least in isolated island lakes. In Tasmania, where the native fish are mostly galaxiids, 9 non-native freshwater fish species have been introduced over the past 150 years, with uncertain ecological outcomes. We evaluated the effects of non-native predatory fishes (NNPF) and various environmental and biological variables on the trophic niche of native fish (galaxiids) and potential cascading effects. We analysed Layman’s food web metrics based on both stable isotope (δ ¹⁵N and δ ¹³C) values and fish stomach contents in 14 shallow Tasmanian lakes along a NNPF abundance gradient. The food web metrics calculated were (1) range of δ ¹³C (CR) and δ ¹⁵N (NR) centroid distance (CD) and (2) standard ellipse area. Our results showed that NNPF relative abundance in the fish catch per unit effort was negatively related to the galaxiids’ trophic niche metrics (e.g., CR_G, NR_G, and CD_G), trophic position, and the pelagic contribution to the diet. Moreover, the proportion of galaxiids in the diet of NNPF was higher in turbid lakes. The zooplankton standard ellipse area was negatively correlated with the pelagic contribution to the NNPF diet, and NNPF relative abundance was positively correlated with the maximum body size of calanoid copepods. While our results suggest a negative effect of NNPF on the trophic niche of galaxiids, the cascading effect on phytoplankton biomass was weak. Non-native predatory fish affect native fish prey, and the outcome of these interactions should be considered for conservation purposes, particularly for island lakes, such as those in Tasmania.

非本地鱼类的入侵威胁到本地动植物和生态系统的功能，尤其是在离岛湖泊中。在塔斯马尼亚州，当地鱼类主要是加拉西虫类，在过去的150年中，引入了9种非本地淡水鱼类，其生态结果不确定。我们评估了非本地掠夺性鱼类（NNPF）的影响以及各种环境和生物学变量对本地鱼类（galaxiids）的营养生态位和潜在级联效应的影响。我们分析了外行的食物网度量基于两种稳定同位素（δ ¹⁵ N和δ ¹³ C）在14浅塔斯马尼亚湖泊值和鱼胃内容物沿着NNPF丰度梯度。计算出的食物网度量分别为（1）的范围δ ¹³ C（CR）和δ ¹⁵ N（NR）的质心的距离（CD）和（2）的标准椭圆区域。我们的结果表明，单位工作量捕捞的NNPF相对丰度与加拉西德人的营养生态位指标（例如CR _G，NR _G和CD _G）负相关。），营养位置以及对饮食的中上层贡献。此外，在浑浊的湖泊中，神经营养素饮食中加拉西德的比例更高。浮游动物的标准椭圆面积与浮游动物对NNPF饮食的贡献呈负相关，而NNPF相对丰度与cal鱼足类的最大体型呈正相关。虽然我们的结果表明NNPF对加拉西虫的营养生态位具有负面影响，但对浮游植物生物量的级联作用却微弱。非本地掠食性鱼类会影响本地鱼类的猎物，出于保护目的，应考虑这些相互作用的结果，特别是对于塔斯马尼亚岛的岛屿湖泊。