Length-Weight Relationships of Eight Fish Species in the World’s Largest Water Diversion Project

. Te study provides the length-weight relationships (LWRs) for eight fsh species, viz. Hemiculter bleekeri , H. leucisculus, Opsariichthys bidens (Xenocyprididae), Carassius auratus, Cyprinus carpio (Cyprinidae), Pseudorasbora parva (Gobionidae), Acanthorhodeus chankaensis, and Rhodeus ocellatus (Acheilognathidae), in the world’s largest water diversion project, namely, the middle route of South-to-North Water Diversion Project (SNWDP). Fish specimens were sampled by benthic fyke-nets, gillnets, multimesh gillnets, and electrofshing equipment seasonally from 2015 to 2020. Te coefcient of determination ( r 2 ) was ranging from 0.964 ( R. ocellatus ) to 0.986 ( H. leucisculus ), and the b values for the eight species were within range of 2.5–3.5. Also, our study updates the information on the maximum total length for four species ( H. bleekeri , H. leucisculus , A. chankaensis , and O. bidens ).


Introduction
Te middle route of South-to-North Water Diversion Project (SNWDP) is the world's largest interbasin water diversion project (32°40′-39°58′N, 111°42′-116°16′E), which originates from Danjiangkou Reservoir and fows northward to Beijing through a 1276 km open canal. When the main canal extends to North China, it passes through the subtropical monsoon humid climate zone and the temperate monsoon climate zone, and the average annual precipitation and the annual air temperature are 542−1173 mm and 14.6-21.2°C, respectively [1,2]. Te main canal is also the largest artifcial river ecosystem in the world, the ecosystem is in its early stages, and the ecosystem balance has not been established. Te fsh community structure is simple which has relatively few fsh species, and dominated by small fshes, and the species diversity is low. Te development of fsh community function is lagging behind, and the top-down efects of the ecosystem is weak. Terefore, it is very necessary to explore fsh diversity, biology, and population dynamics for better conservation in this project [3,4].
Te length-weight relationships (LWRs) of fsh species are important for estimating the weight of a specimen from the length, and the reverse is also true [5,6]. Together with data on growth rates, sex ratio, length-at-age, fecundity, size at frst maturity, spawning stock biomass, and recruitment, LWRs can greatly assist in the research of population status and management [3]. In this study, the LWRs for eight species from the middle route of SNWDP are presented. Te results can provide basic biological and scientifc knowledge on the fsh ecological regulation for the administrative department.

Materials and Methods
We used benthic fyke-nets (mesh size: knot to knot, 5 mm), gillnets (mesh size: knot to knot, 60, 80, and 100 mm), multimesh gillnets (mesh size: according to European standard, 5-55 mm), and electrofshing equipment (36 V, 12 A) to collect seasonal samples of fsh between 2015 and 2020. A total of ten sampling sites distribute along the main canal, which are Dengzhou section (32°43′6″N, Total length (TL) and body weight (W) were measured with 0.1 cm and 0.1 g accuracy, respectively. Te estimation of LWRs was calculated as log (W) � log (a) + blog (L), where W is the body weight (g) and L is the total length (cm). Te parameters and statistical test were analyzed by using R software (version: 4.1.1). Prior to regression analysis, outliers were detected and removed by using log-log plots [3]. Te 95% confdence limits for a and b (95% CL) were determined for the parameters, as well as the coefcients of determination (r 2 ). When r 2 < 0.95, the regression was repeated after removing outliers [3,7].
In addition, ethics approval for all experiments and handling of fshes in our study complied with the animal welfare regulations of the Government of China and followed the ethical rules of the Institutional Animal Care and Use Committee of the Institute of Hydrobiology, CAS (Approval ID: Keshuizhuan 08529).

Results
Te results of LWRs and descriptive statistics are presented in Table 1. Te regressions for all fsh species were statistically signifcant (P < 0.01), with the coefcient of determination (r 2 ) ranging from 0.964 to 0.986. Based on FishBase data (https:// www.fshbase.org, version: 08/2022), our study updates the information on the maximum total length for four species, including Hemiculter bleekeri, H. leucisculus, Acanthorhodeus chankaensis, and Opsariichthys bidens.

Discussion
In this study, the r 2 values of all fsh species were >0.95 and the range of b values was between 2.996 and 3.341, which was consistent with the expected range of 2.5-3.5 [3]. Many factors, such as growth phase, gender, food, fshing behavior, seasonality, and temperature, may lead to the diferences of LWRs [3,5,6]. However, abovementioned factors were not taken into account in this study. New records of maximum total lengths of four species are recorded for FishBase [8], of which the H. bleekeri recorded in FishBase was 20.2 cm, new record is 25.2 cm, H. leucisculus recorded 27.4 cm, new record is 29.0 cm, A. chankaensis recorded 13.5 cm, new record is 14.4 cm, and for O. bidens recorded 21.9 cm, new record is 26.1 cm. Tis study provides scientifc data on LWRs for eight fsh species, which can be useful for fsh resource conservation and management in the middle route of SNWDP.

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

Conflicts of Interest
Te authors declare that there are no conficts of interest.