Length-Weight Relationships and Growth Patterns of Eight Indigenous Fish Species from Lancang River, Southwest China

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Introduction
Te Lancang-Mekong River is the longest river in Southeast Asia.As a longitudinally important international river, the Lancang-Mekong River watershed covers various landscape types and has extremely high fsh biodiversity [1].It is the second river with the highest freshwater biodiversity worldwide only after the Amazon River, having an estimated 890 species of freshwater fsh [2,3].Nearly 200 fsh species have been recorded in the river within China, most of which are indigenous species [1].However, with the rapid population growth and economic development of countries in the river basin, especially the cascade development of the substantial hydropower resources in the upper and middle reaches, fsh diversity and fshery resources of the Lancang River are experiencing serious threats.Habitat loss and fragmentation, water pollution, overfshing, and alien species invasion are the main threats and have resulted in signifcant decline in fsh diversity and homogenization of fsh assemblages [4][5][6].Despite these threats on local fsh communities, basic biological information on most indigenous fsh species in the Lancang River is limited [3].It is necessary to explore fsh biology, population dynamics, and fsh diversity of Lancang River to implement conservation and management measures for the protection of local fsh assemblages.
Length-weight relationships (LWRs) are important in fsh biology, ecology, fshery management, and conservation.Tey allow the determination of fsh weight from length or vice versa, facilitating the production evaluation of fsh populations and providing information on growth patterns [7,8].Furthermore, LWRs facilitate biometric and morphological comparisons between fsh species in the same taxonomic group or between fsh populations from diferent regions or time periods [9,10].Te "b" value calculated from length-weight relationship is usually used to describe the growth patterns of fsh.When it does not difer signifcantly (P > 0.05) from the ideal value (b = 3), weight growth is considered isometric, indicating that a fsh proceeds in the "same" dimension as the cube of length.Otherwise, weight gain is allometric, including positive (b > 3) and negative (b < 3) [11].Te condition factor (K) is another index calculated from length and weight measurements that refects the energy and nutritional status of fsh at the individual level [12].It is usually used to assess the fullness, nutrition, and the efect of environmental variability on fsh and can be used as an efective, readily available indicator of population status [13][14][15].Relative weight (W r ) is another popular method for assessing the condition of freshwater fsh, refecting ecological and physiological optimality within fsh population, and this index validates direction comparison of individuals condition across populations [10,16,17].
Indigenous fshes in the Lancang River are important components of the local biodiversity and aquatic food webs.Some indigenous fshes are important components of local fsheries, such as Schizothorax lissolabiatus, Tor sinensis, and Mystacoleucus lepturus [18,19].However, there are few data about their biological traits.Little information is available on the LWR and growth pattern of these fshes.To expand the biological knowledge of these species and provide basic data for conservation, this study provides the LWRs, condition factors, and relative weights of eight indigenous species belonging to three families from the Lancang River for which there is no information regarding the LWR, even in FishBase [20].

Study Area and Sample Collection.
Samples were collected from the Lancang River and their tributaries (i.e., Jidu, Weiyuan, Buyuan, and Nanla rivers) in Southwest China from November 2018 to September 2021 (Figure 1, Table 1).Drift gillnets (20-40 m long, 1-3 m high, and mesh size of 1-5 cm), trap nets (20 m × 50 cm × 50 cm, mesh size: 1 cm), and electrofshing (20 A, 1 V, 3000 W) were used to obtain fsh samples.After they were caught, the specimens were identifed to the species level according to the Fishes of Yunnan, China [18,19], and Checklist of Fishes of Yunnan [21].All scientifc names were checked against FishBase [20].For each individual, standard length (SL, cm) was measured to the nearest 0.1 cm using a fsh measuring board, and body weight (BW, g) was measured to the nearest 0.1 g using an electronic balance (Lichen, TD50002A).All handling procedures were performed according to the Laboratory Animal Administration Regulations of China.
Te LWRs were calculated using the power function.Condition factor (K) and relative weight (W r ) were used to assess condition of individuals of the eight fsh species.Equations used to calculate these indices were expressed as follows: where ( 1) is used to calculate LWRs, (2) is used to calculate the condition factor, and (3) is used to calculate the relative weight and W is the body weight (BW, g), L is the standard length (SL, cm), a is the intercept of the regression, b is the allometric coefcient, K is the condition factor, and W r is the relative weight.According to Froese [10], prior to the 2 Journal of Applied Ichthyology regression analysis of BW on SL, logarithmic transformation was performed and log-log plots of length and weight were used to eliminate outliers.No outliers were found, so the loglog plots were not shown in the study.Parameters a and b were estimated using linear regression analysis based on 10 logarithms: log BW � log a + b log SL.Coefcient of determination (r 2 ) calculated from the regression analysis was used to evaluate the ft of LWR estimate.Te 95% confdence interval (Cl) of parameters a and b was estimated.

Signifcance Testing.
Te covariance analysis (ANCOVA) method was used to test whether there were seasonal diferences of the allometric coefcient b.Independent samples t-test was performed among sampling seasons to determine the intraspecifc diference of K and W r .Signifcant variation in the estimates of b of the lengthweight relationship was compared with the expected value (ideal value b = 3) and was tested by t-test.Te equation used to compute the t-statistic is where s.d.

Results and Discussion
3.1.Length and Weight Analysis.In total, 534 specimens belonging to three families, eight genera, and eight species were collected and studied for their LWRs and growth patterns.Te fsh species were S. lissolabiatus, Poropuntius huangchuchieni, T. sinensis, Scaphiodonichthys acanthopterus, M. lepturus, Hemiculterella macrolepis, Schistura porthos, and Glyptothorax lampris.Te LWRs for the eight species were reported for the frst time to FishBase.Moreover, the new maximum standard length for 5 fsh species, namely, S. lissolabiatus, P. huangchuchieni, T. sinensis, S. acanthopterus, and M. lepturus, was also reported for the frst time to FishBase [20].Te sample size; size range of SL and BW; length-weight relationship parameters a and b and their 95% confdence interval; coefcient of determination r 2 ; and growth pattern are given in Table 2.
According to the fndings of this study, all fsh species analyzed showed a strong correlation between length and weight.Statistical length-weight relationships for all eight fsh species were highly signifcant (P < 0.001), with all r 2 values greater than 0.90, indicating that the LWR estimates for all species ft well and were highly reliable.Te values of parameter b for all 8 species ranged between 2.5378 and 3.1732 and remained within the expected range of 2.5-4.0 [10].Te b values of the LWRs of S. lissolabiatus and T. sinensis in this study difered from those of other populations [22,23], indicating an intraspecifc diference among diferent geographic populations.Intraspecifc differences of the b values and growth patterns in diferent seasons were also observed in this study.Te b value of S. lissolabiatus in spring was signifcantly higher than that in autumn (ANCOVA, F � 16.179, P < 0.001).It showed positive allometric growth in spring (t-test, t � 0.403, P < 0.05) and isometric growth in autumn (t-test, t � 1.346, P > 0.05).For P. huangchuchieni, the b value of this fsh in spring was signifcantly lower than that in autumn (ANCOVA, F � 23.759, P < 0.001).Growth pattern of this fsh was negative allometric in spring (t-test, t � 3.454, P < 0.05) while positive allometric in autumn (t-test, t � 3.802, P < 0.05).Te b value of S. acanthopterus in spring was lower than that in summer (ANCOVA, F � 4.102, P < 0.05), and the growth pattern of this fsh in spring was negative allometric in spring (t-test, t � 2.357, P < 0.05) and isometric in summer (t-test, t � 1.654, P > 0.05).For M. lepturus, this b value in spring was larger than that in summer (ANCOVA, F � 1.939, P < 0.05); this fsh showed isometric growth pattern in spring (t-test, t � 2.357, P > 0.05) and negative allometric growth pattern in summer (t-test, t � 1.654, P < 0.05).Tese seasonal variations in the b value and related growth pattern may relate to diferences in the sampling season, developmental phases, and stomach fullness of fshes at the time [10,11].Besides, some other factors would afect the b parameter, for example, sex [24], size classes [25], diferent time periods [26,27], or even diferent geographic populations [28].To increase the

Glyptothorax lampris
Fowler, 1934 * Win.33 4.5-10.06.0 ± 1.30 1.9-14.5 4.0 ± 2.68 0.0305 0.0235-0.03742.6632 2.5345-2.79200.9826 N * Newly recorded LWR to FishBase; + tentative estimation due to limited size range; bold, new maximum record of standard length to FishBase; n, sample size; a and b, regression parameters; Cl, confdence limits; r 2 , coefcient of determination; P, positive allometric growth; I, isometric growth; N, negative allometric growth; S.D., standard deviation (SL, cm; BW, g). 4 Journal of Applied Ichthyology reliability of description of the isometric or allometric growth of fsh based on the average b value, all the aforementioned factors were recommended to consider [10].

Condition Factor and Relative Weight Analysis.
Condition factors (K) of the eight fsh species ranged from 0.85 to 6.40 (Table 3).Te lowest mean condition factor was observed in H. macrolepis in spring, with a mean value of 0.97 ± 0.06, while the highest mean condition factor was observed in S. acanthopterus in summer, with a mean value of 2.39 ± 1.19.Independent samples t-test showed that the condition factors of P. huangchuchieni and M. lepturus in spring were signifcantly diferent from those in summer (P < 0.05), respectively.No signifcant diferences were observed in S. lissolabiatus, T. sinensis, and S. acanthopterus across sampling seasons, respectively (P > 0.05).Tis seasonal diference may relate to their growth periods at the sampling time [10].For P. huangchuchieni and M. lepturus, their breeding season was in spring, mainly from April to May [18,19], and they gained weight as the gonads mature in spring, so their K mean values in spring were higher and diferent from summer.As for S. lissolabiatus and S. acanthopterus, the reproductive season was mainly in March and April, and for T. sinensis, it was mainly in November and December [18,19]; their reproductive season ended or had not come at the sampling time, and no seasonal diferences of ftness for these three fshes were observed.Besides, fshing pressure could also afect their condition factor because S. lissolabiatus, T. sinensis, and M. lepturus were important components of local fsheries [18,19].According to Haberle et al. [29], the body length, body weight, and average condition factor increased with an increase in fshing pressure but decreased with an increase in population abundance.Diferences of condition factor of H. macrolepis, S. porthos, and G. lampris across sampling seasons were not discussed because these fshes were captured only in one season.
Relative weight (W r ) conveys important physiological components of fsh life history (e.g., lipid storage, body morphology, and growth rate) and ofers a strong, accessible metric for managers to assess the overall health and ftness of fsh populations, as well as population-level responses to ecosystem disturbances [30].According to Anderson and Neumann [31], a relative weight (W r ) of an individual or population less than 100 may indicate problems, such as low prey availability or high predation pressure; a relative weight (W r ) greater than 100 indicates sufcient prey or low predation pressure.Te mean relative weight range of the eight fsh species analyzed ranged from 100.29 to 108.18 (Table 3), indicating a balance between prey availability and predator density of these fsh populations in their habitat.Also, there was no signifcant diference of relative weight across sampling seasons for 5 fsh species, namely, S. lissolabiatus, P. huangchuchieni, T. sinensis, S. acanthopterus, and M. lepturus (all P > 0.05).Because there was only one-season dataset, diferences of relative weight of H. macrolepis, S. porthos, and G. lampris across seasons were not discussed.

Conclusions
Tis study provides a basic understanding of the LWRs and condition factors of eight fsh species indigenous to the Lancang River and their tributaries in Yunnan Province, China.LWRs for the eight species are published herein for the frst time for the FishBase.New records of maximum standard length for fve fsh species were recorded.Since some indigenous fshes analyzed are important components of local fsheries, such as S. lissolabiatus, T. sinensis, or M. lepturus, our results will be useful resource for future fsheries research evaluating the health status of these populations.Besides, indigenous fshes in the Lancang River are important components of the local biodiversity and aquatic food webs.However, diferences across fshing gears, size ranges, reproductive stage, and sexes were not evaluated in the present study.Further research involving the factors that afect fsh growth is required to provide additional valuable information for local fsh conservation and fshery management.We suggest that further studies include longterm monitoring of fsh resources; conduct community and population dynamics analysis; comprehensively evaluate the Journal of Applied Ichthyology relationship between aquatic environment and fshery resources; and, based on these research studies, conduct scientifc fshery stocking and fshing management to ensure that the river has sustainable fshery production while supporting other ecological service functions.

Figure 1 :
Figure 1: Sampling sites of the Lancang River and their tributaries.Te area enclosed by the blue contour line is the Lancang River basin.JDR, Jidu River; WYR, Weiyuan River; BYR, Buyuan River; NLR, Nanla River.

Table 1 :
Sampling sites and dates of the eight fsh species from the Lancang River, China.Specimens were collected from the mainstream and tributaries of the Lancang River.U, including upper stream of the Lancang River, Jidu River; M, including middle stream of the Lancang River, Weiyuan River; D, including downstream of the Lancang River, Buyuan River and Nanla River; ○, fshes were collected.

Table 2 :
Descriptive statistics and estimated parameters of LWR (BW �