Length–weight relationships are widely used in fisheries research because they help convert measurements of fish length into estimates of weight and biomass. A related measure, Fulton’s condition factor, describes how heavy a fish is for its length and can offer clues about its condition. Xinjiang’s inland waters support distinctive freshwater fish communities, but comparable data remain limited for many local species. The Upstream Reservoir once supported abundant fish resources; pressures including overfishing, introduced species and expanding human activity have contributed to their decline. Before this study, a length–weight relationship had been documented there for only one species, leaving managers with little species-specific information for monitoring the wider fish community.
A study (DOI: 10.48130/jai-0026-0002) published in Journal of Applied Ichthyology on 28 August 2026 by Jie Wei's & Zhulan Nie's team, Tarim University, reports significant length–weight relationships for all 13 species and documents substantial differences in their growth parameters and condition factors.
The researchers sampled eight sites representing different parts and habitats of the reservoir, including inflow and outflow areas, shallow margins and deeper water. Seasonal surveys ran from March 2024 to May 2025, with sampling twice per quarter. The team used gillnets with multiple mesh sizes and wire-mesh traps, then identified the captured fish and measured each specimen's total length and body weight. They pooled measurements regardless of sex, fitted a separate length–weight model for each species and calculated Fulton’s condition factor. Before estimating the models, they excluded measurements identified as extreme outliers by a statistical check. The resulting length–weight relationships were statistically significant for every species. Their growth exponent, known as b, ranged from 2.553 to 3.409: six species had values below 3, while seven had values above 3. Hemiculter leucisculus had the highest value and Misgurnus anguillicaudatus the lowest. Model fit also varied. Length accounted for a particularly high proportion of the variation in weight for Pelteobagrus fulvidraco, whose model had a coefficient of determination of 0.995; the corresponding figure for M. anguillicaudatus was 0.698. Across the fish studied, recorded condition-factor values ranged from 0.263 to 2.664. The widest variation in condition within a species occurred in H. leucisculus, while Carassius auratus showed the least. These measurements provide reference points for comparing fish collected in later surveys, although differences in body shape mean that condition factors should not be read as a simple health ranking across species. The researchers also note that the numbers of fish sampled differed among species, which introduces uncertainty into some estimates. Sex was not assessed, and surveys at this frequency may have missed shorter-term seasonal changes.
The study gives the Upstream Reservoir its first set of length–weight estimates covering 13 freshwater fish species. By pairing those estimates with condition-factor measurements, it provides practical reference data for following local fish populations as conditions change. The equations can support future weight and stock estimates when researchers collect length data, but their accuracy should be checked as new samples become available. Further surveys, especially those with more frequent sampling and larger numbers for less common species, could clarify seasonal patterns and strengthen the evidence used in fishery management.
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Reference
DOI
10.48130/jai-0026-0002
Original Source URL
https://doi.org/10.48130/jai-0026-0002
Funding information
This research was supported by the Saline-tolerant fish large size seed breeding technology and demonstration (No. 2025YD016), the Analysis of species availability and cryptic diversity of schizothorax fishes based on morphology and DNA barcoding techniques (No. 32460920), the Northwest inland saline-alkali land characteristic aquaculture technology integration and model construction (No. 2023YFD2401004), the Survey of macroaquatic communities in key lakes of Xinjiang (No. 2022xjkk150403), and the Postgraduate Innovation Project of Tarim University (No. TDBSCX202404).
About Journal of Applied Ichthyology
Journal of Applied Ichthyology (e-ISSN 1439-0426; p-ISSN 0175-8659) is an open-access, peer-reviewed journal dedicated to publishing high-quality research on applied ichthyology, aquaculture, and marine fisheries, including management of fisheries resources, fisheries ecology, fish health and pathology.