Length-Weight Relationships of Four Fish Species of the Upper Yangtze River, Sichuan, China

In this study, the length-weight relationships were determined for four fsh species of the upper Yangtze River, Sichuan province, China. Te fsh were collected by drift net (mesh size: 4 cm × 4cm) and ground bamboo cages (1cm × 1cm) from Yalong River, Laixi River, Pingtung River, and Baoxing River. Samples were collected from March 2017 to December 2022. According to the length-weight function equation ( W � aL b ), r 2 values ranged from 0.960 to 0.991 and the b values of LWRs ranged from 2.916 ( Megalobrama pellegrini ) to 3.095 ( Claea dabryi ).


Introduction
Yangtze River, the longest river in Asia, is the habitat of more than 400 species of fsh [1]. Te upper reaches of the Yangtze River are rich in fsh resources and have a complex ecological environment. Tere are more than 240 species of fsh distributed here [2], including more than 40 species of rare and protected fsh [3], such as Acipenser sinensis (Gray, 1835,) Acipenser dabryanus (Duméril, 1869), Hucho bleekeri (Kimura, 1934), and Procypris rabaudi (Tchang, 1930) and some unique species such as Schizothorax sinensis (Herzenstein, 1889), [4] and Claea dabryi (Sauvage, 1874) [5]. Keys [6] proposed an equation describing the relationship between the length and weight of fsh, and Froese [7] further elaborated on the LWRs for specifc fsh. Terefore, this method of analyzing fsh population characteristics has been recognized widely and used as a fundamental tool for fshery research and management [8]. To compare the relationship between standard length and body weight of fsh from March 2017 to December 2022, four fsh species distributed in the upper reaches of Yangtze River were collected and the relationships between body weight and standard length were analyzed.

Materials and Methods
Fish samples were collected twice a year from March 2017 to December 2022. Te sampling tools included drift nets (mesh size: 4 cm × 4 cm) and ground bamboo cages (1 cm × 1 cm). Te sampling area includes the Yalong River, Laixi River, Pingtung River, and Baoxing River (Table 1). Te collected fsh were frstly classifed according to the morphology by referring to the the fshes of Sichuan (Ding, 1994) and then verifed by mitochondrial DNA marker. Te standard length is accurate to 0.1 cm and body weight accurate to 0.1 g. During data analysis, a simple linear regression model was used to ft each species data with logarithmically converted data to determine the 95% confdence interval (CI) of parameters a and b, and the lengthweight function equation (W � aL b ) [7].

Results
Te descriptive statistical results of sample number (N), length range, weight range, parameters a, b, 95% confdence interval, and correlation coefcient (r 2 ) of the four fsh species were shown in Table 2.

Discussion
Studies have shown that the standard length-weight equation (W � aL b ) refected the living environment and growth rate of fsh. It is generally believed that the larger a value is, the better the conditions such as feed and water quality the living environment [9]. b value refects the growth type of fsh, and the parameter b was usually between 2.5 and 4.0 in the natural environment [7]. b � 3 indicated that the growth of the population's length and body weights was constant; b > 3 indicated that the body weight of fsh was accelerated growth; otherwise, the standard length of fsh was accelerated growth [9]. Based on this theory, two of the four fsh species in this study were in a natural state (b > 3), indicating that the body weights were increasing rapidly. Te b value suggested their living environment was relatively stable. In contrast, the other two fsh species were more or less exposed to environmental disturbance. Te a value ranged from 0.0102 to 0.0242, which also confrmed that the fsh were signifcantly afected by their living environment. Tis was in agreement with the previous research result [9].
Te recent report on Claea dabryi (Sauvage, 1874) demonstrated that the standard length ranged from 4.3 to 6.4 cm and the body weight ranged from 1.0 to 3.6 g [10]. Te range of standard length and body weight of our study exceeds previously reported maximum or minimum values for this species. Megalobrama pellegrini (Tchang, 1930) was recently reported to have the standard length of 19.6-48.5 cm and the body weight of 80.77-1726.8 g [8]. Te result of this study exceeds previously reported minimum values for this species. Similar situation was observed in Schizopygopsis malacanthus (Herzenstein, 1891) in which reported that the standard length of this fsh was 5.8-52.8 cm, and the body weight was 1.4-442.7 g [11]. Te length-weight relationships of Schizothorax sinensis (Herzenstein, 1889) have not been reported. Te present results are of great signifcance for the protection of endemic fsh and the scientifc management of the ecosystem in Yangtze River.

Data Availability
Te data that support the fndings of this study are available from the corresponding author upon reasonable request.

Ethical Approval
Te study protocol was approved by the Animal Care and Use Committee of the Fishery Institute of the Sichuan Academy of Agricultural Sciences (20170301001A) and was performed in compliance with the guidelines for the care and use of laboratory animals.

Conflicts of Interest
Te authors declare that they have no conficts of interest.