Length–weight relationship and condition factor of roach Rutilus rutilus in lentic waterbodies of Uzbekistan

Abstract

This study investigates the length–weight relationship (LWR) and condition factor of roach, Rutilus rutilus, from seven lentic water bodies in Uzbekistan, including reservoirs and drainage lakes in the Syrdarya, Zarafshan, and Surkhandarya river basins. These habitats, formed mainly during the large-scale irrigation developments of the late 20th century, now support abundant roach populations that have become commercially significant since the 2000s. Samples were collected from commercial catches in March–April 2024–2025 using gill nets (mesh 16–50 mm). Total length (TL), standard length (SL), and weight (W) were measured. The LWR was modeled using both power and log-transformed equations, and Fulton’s condition factor (K) and rel a tive condition factor (Kn) were calculated. Results revealed strong positive correlations between SL and TL in all stocks. LWR exponents (b) ranged from 2.81 to 3.23, indicating predominantly isometric or slightly positive allometric growth, except for East Arnasay Reservoir (b = 2.81) and Lake Karakir (b = 2.93), which showed slight negative allometry. Fulton’s K averaged 1.14–1.26 across sites, suggesting generally good condition, though roach in Lakes Aydarkul and Tuzkan had lower fatness, likely linked to increasing salinity (8–12‰) and reduced freshwater inflow. Kn values averaged around 1.0 for all populations, indica t ing that observed weights closely matched those predicted by LWR equations and reflecting stable ecological conditions. The findings highlight the adaptability of roach to diverse hydrological conditions, including brackish drainage lakes, and their ability to form sustainable commercial stocks in Uzbekistan’s artificial and semi-natural water systems. The data provide the first d e tailed LWR and condition factor assessments for R. rutilus in the region, offering valuable baselines for fisheries management. Differences in growth patterns and body condition among water bodies likely reflect a combination of environmental factors, including salinity, food availability, and hydrological regime stability. From a management perspective, monitoring K and Kn values over time may serve as an effective tool for detecting shifts in fish health related to climate variability, water quality changes, and anthropogenic pressures. Overall, this study expands the understanding of roach biology in arid and semi-arid i n land water ecosystems, where climatic extremes and human-modified hydrology shape fish population dynamics. The observed capacity of roach to maintain favorable condition factors in most habitats supports their continued role as a key component of Uzbekistan’s inland fisheries, although the ir declining condition in the more saline lakes signals the need for targeted manag e ment actions to sustain productivity.