After 150 years of introduction of the brown trout Salmo trutta in Himalaya, the native species’ response to this globally pervasive invader, is still unknown. Here, we investigate the effects of invasion of brown trout on native snow trout Schizothorax richardsonii, one of the most primitive species that co-evolved with the Himalayan orogeny. We contrast two natural river systems which harbour snow trout in the absence (allopatry) and presence (sympatry) of brown trout. We put forth that sympatric snow trout adapted to a ‘fast’ life history with maturation at a smaller length, greater fecundity and smaller egg diameter to cope with brown trout invasion. However, investment in a reproductive-somatic trade off was evident with a disrupted size structure and reduced abundance as compared to the allopatric population. Although the fast life history adaptations of snow trout might increase their competitive ability with invasive brown trout, trading off the somatic fitness in the process seemingly acts as a deterrent to longevity. We attribute the plastic responses of snow trout to their plausible inherent potential of sustenance and recovery from high invasion pressures. The popularity of brown trout as a sport fish in Himalaya however poses extraneous propagule pressure on the snow trout, which warrants quantification through future research.

经过150多年的引进的褐鳟鱼的褐鳟在喜马拉雅，本地物种对这个全球普遍存在的入侵者响应，仍是未知数。在这里，我们调查入侵褐鳟对本地雪鳟Schizothorax richardsonii的影响是与喜马拉雅造山运动共同进化的最原始的物种之一。我们对比了两种自然河流系统，它们在不存在（变色层）和存在（象征性）褐鳟的情况下藏有鳟鱼。我们提出同胞雪鳟适应“快速”的生活史，具有较短的长度，更大的繁殖力和较小的卵直径，可以应对褐鳟的入侵。然而，与异源种群相比，在生殖体平衡上的投资是明显的，其大小结构被破坏且丰度降低。尽管适应鲑鱼的快速生活史可能会提高其与侵入性褐鳟的竞争能力，但是在此过程中权衡体能似乎对延年益寿起到了威慑作用。我们将鳟鱼的塑性响应归因于它们在高入侵压力下维持和恢复的合理固有潜力。然而，褐鳟在喜马拉雅山中作为运动鱼类的流行给雪鳟造成了不必要的繁殖压力，这需要通过未来的研究进行量化。