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 P. fluviatilis. 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 P. fluviatilis 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&ndash: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&ndash:5, with ages 1&ndash: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 (Lt) and body mass (Wt) was modeled as Wt = 4.298 &times: 10&minus:5&nbsp:Lt2.85 (R2 = 0.998, n = 296). The von Bertalanffy growth equations were Lt = 652.866 [1 &minus: e&minus:0.108(t+0.778)] and Wt = 4990.21 [1 &minus: e&minus:0.108(t+0.778)]2.85, with a growth coefficient K = 0.108. The inflection point of growth was determined to be 1.9 years by fitting growth rate and acceleration equations. The b &lt: 3 indicates allometric growth, where body length increases faster than body mass, suggesting that P. fluviatilis 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.