Study on Morphology, Age and Growth of River Perca fluviatilis in Kalasuke Reservoir, Xinjiang, China

In late August and mid-November 2024, and late February and mid-May 2025, four surveys were conducted in the Kalasuke Reservoir section of the Irtysh River, resulting in the collection of 296 samples of <i>P. fluviatilis</i>. Sampling tools included drift gillnets with a mesh size of 5 cm and an outer mesh size of 10 cm, bottom cages with a mesh size of 1 cm, and fishing rods (4.5 m and 5.4 m). The age structure and growth characteristics of <i>P. fluviatilis</i> in the reservoir were analyzed. Results showed that the body length of the sampled fish ranged from 100.53 to 305.30 mm, with the dominant length group being 100.53-150.00 mm, accounting for 90.09% of the total. Body mass ranged from 24.20 to 490.20 g, with the dominant mass group below 66.5 g, accounting for 89.86%. The age composition of the population consisted of age classes 1-5, with ages 1-2 years old being dominant, accounting for 96.2% of the total samples. Among these, 1-year-old individuals were the most abundant, accounting for 78.3%, while older fish were relatively scarce. The relationship between body length (<i>L_t</i>) and body mass (<i>W_t</i>) was modeled as <i>W_t</i> = 4.298 × 10^-5<i>L_t</i>^2.85 (<i>R</i>² = 0.998, <i>n</i> = 296). The von Bertalanffy growth equations were <i>L_t</i> = 652.866 [1 - <i>e</i>^-^0.108(<i>^t</i>^+0.778)] and <i>W_t</i> = 4990.21 [1 - <i>e</i>^-^0.108(<i>^t</i>^+0.778)]^2.85, with a growth coefficient <i>K</i> = 0.108. The inflection point of growth was determined to be 1.9 years by fitting growth rate and acceleration equations. The <i>b</i> < 3 indicates allometric growth, where body length increases faster than body mass, suggesting that <i>P. fluviatilis</i> prioritizes elongating its body to enhance swimming ability and expand its range, while accumulating muscle and fat at a slower pace. Principal component analysis (PCA) revealed that the cumulative contribution rate of the first three principal components was 55.45%, reflecting the morphological characteristics of the species. The accuracy of discriminant analysis for sex determination based on external morphology was 67.20%, indicating limited reliability in gender identification using only morphological traits.