Length–Weight Relationship, Age, and Growth of Invasive Carassius auratus in Lugu Lake, China

<i>Carassius auratus</i>, a key invasive species in the high-altitude Lugu Lake (2690 m) in China, was studied to assess its length-weight relationship, age structure, and growth patterns using scale-based age determination. A total of 670 specimens were collected via systematic gillnet surveys conducted in May and October 2023. The population comprised five age groups (0+ to 4+), with 0+ and 1+ individuals dominating (69.40%). Body lengths ranged from 36 to 178 mm (mean: 93.73 mm), peaking at 60-70 mm (33.88%). Body weights varied from 1.3 to 175 g (mean: 33.60 g), with 1.3-10 g as the dominant range (26.27%). The length-weight relationship was modeled as <i>W</i> = 2 × 10^-5<i>L</i>^3.026 (<i>n</i> = 670, <i>R</i>² = 0.985), indicating isometric growth. Von Bertalanffy growth parameters indicated an asymptotic length (<i>L</i>∞) of 401.57 mm, an asymptotic weight (<i>W</i>∞) of 484.38 g, a growth coefficient (<i>k</i>) of 0.0721, and a theoretical age at zero length (<i>t</i>₀) of -1.6174 years, with an inflection point at 6.66 years. The simplified age structure and dominance of young cohorts suggest rapid population expansion, highlighting the urgent need for management strategies to mitigate ecological impacts on this fragile plateau ecosystem.