| Elongate loach (Leptobotia elongata) and Redlip loach (Leptobotia rubrilabris), belong to Leptobotia of Cobitidae, Cypriniformes, are native species of the Yangtze River. These two species mainly distributed in the upper reaches and branches, due to over fishing and development of hydropower, the habitat of these fish species has been in serious danger. Elongate loach is listed in "China Species Red List". This study aims to provide a data record and comprehensive analysis of Elongate loach and Redlip loach population in the Yangtze River. The field inventory was conducted in September2010to December2012,1025specimens of elongate loach and1658specimens of redlip loach were collected from the upper reaches of the Yangtze River, Based on the inventory data, the analysis of the biological characteristics of individual fish, population dynamics, genetic structure and variation of elongate loach and redlip loach are carried out, the findings of this study are:1. Although there were140fish species distributed in the study area. However, only102species were collected which belong to7orders and17families in this study. Among the collected species,20species were endemic of the upper reaches of the Yangtze River. The species similarity is highest between the study area and the Tuo River, while the lowest species similarity is between the study area and the Jinsha River. Comparison with the historical data indicates that the distribution area of elongate loach and redlip loach changed. Elongate loach can be collected in all section in the upper reaches of the Yangtze River except the Tuo River, whereas redlip loach substantially disappeared in the Jinsha River, the Tuo River and the Jialing River, and samples were merely collected in mainstream and the Minjiang River recently. The average annual catches of elongate loach have been dramatically decreased more than5tonnes from the last decade. Reflecting field survey, redlip loach also experiences significant fishing pressure in the study area.2. Both Elongate loach and redlip loach have clear annulus differences on otolith, vertebrae and opercular. The ability of discriminating elongate loach and redlip loach decrease as the order as: otolith, vertebrae and opercular decrease. The average error between otolith and vertebrae is higher than that of otolith and opercular. Otolith was selected as verification for identifying age of elongate loach and redlip loach. Observed in transmitted light, translucent band and opaque band arranged in circles on the cross-section of otolith, and the separation phenomenon widespread in the otolith primordial of redlip loach. Results of marginal growth increment showed that new ring of otolith formed mainly from March to June both in elongate loach and redlip loach.The relationship between otolith radius and body length of elongate loach and redlip loach were linear correlation. Results of age identification showed that the collected elongate loach samples are in9age groups from1to9ages, the range of body length is from59to461mm, and the weight is from3.1to1333.7g. While the redlip loach samples are in6age groups from2to7ages, the body length is from70to166mm, and the weight is from4.4to60.9g. Because of no significant difference of growth parameters obtained from back-calculation body length and Shepherd method, the average value of the parameters estimated from two methods were taken advantage of as the basic data for the following analysis. In terms of elongate loach, b=3.085, k=0.133/year,L∞=654.99mm, t0=-0.049year and ti=8.42years; for redlip loach, b=2.988, k=0.232/year, L∞=220.17mm, t0=-0.053year and ti=4.67years. Growth equation of elongate loach is Lt=654.99(1-e-0.133(t+0.049),and that of redlip,oach was Lt=220.17(1-e-0.232(t+0.053)). growth characteristics of the two species were significant different: elongate loach grows more slowly with relative large L∞and high inflection point of the weight growth. But the redlip loach grows faster with relative small L∞and lower inflection point of the weight growth.The diet of elongate loach consisted of21prey items from a widely array of biological groups which belong to8categories, while the diet of redlip loach consisted of15prey items which belong to7categories. Elongate loach mainly feeded by fish, crustaceans, molluscs, insects and so on, its main food source were gammarid and small fish (weight percentage%W>75%). Redlip loach mainly feeded by crustaceans, molluscs and insects, and the major food were gammarus and the larvae of Aeshnidae (weight percentage%W>65%). Prey diversity and prey evenness in a medium level in both loaches, which indicated the high concentration of dominant species in diets. It can be concluded that elongate loach mainly feeded by larger benthic fauna, and redlip loach mainly feeded by smaller benthic fauna.Sex ratio of elongate loach and redlip loach were1.238:1and1.222:1.The minimum ages of individuals at first maturity were2.29year and3.48year, with corresponding body length of175.40mm and123.04mm, respectively. Average egg diameters of mature individuals were1433.40±236.20μm and1361.40±214.40μm, respectively, and the style of spawning of them were one-off. Absolute fecundity and relative fecundity were22484±6422egg,7224±2972egg and58.74±15.64egg/g,251.1±23.7egg/g, respectively. Survey on the early age fish population and coefficient of maturation analysis showed that the spawning activity of both elongate loach and redlip loach took place from June to July.3Population parameters estimated from length-converted catch curve and other empirical formulas were derived:For elongate loach:Z=0.810, M=0.208, E=0.740and LC=103.96mm. For redlip loach:Z=1.580, M=0.393, E=0.750and LC=91.75mm. According to length-based cohort analysis (LCA) model, the average annual stock biomass (B) of elongate loach were8.00tonnes and8.09tonnes, the maximum sustainable yield (MSY) were4.08tonnes and4.79tonnes, respectively in2011and2012. The average annual stock biomass (B) of redlip loach was2.63tonnes and2.39tonnes, the maximum sustainable yield (MSY) was1.10tonnes and1.01tonnes, respectively in2011and2012. According to Beverton-Holt dynamic model, the current exploitation ratios (0.740and0.750) were higher than the maximum exploitation ratio (0.430and0.636). These results suggested that both elongate loach and redlip loach had been over-exploited.4According to the survey results from2010to2012, the average fecundity of elongate loach and redlip loach were0.62×108ind and0.52×10ind at jiangjin section in the upper reaches of the Yangtze River. The results of spawning ground showed that18sections and10sections were suitable for elongate loach and redlip loach to spawn. The major spawning ground for elongate loach were Mituo town to Huangshiba village, Tongchewan village to Loufangtou village, Chaxiting village to Chishui estuaries and Zhuyangxi town to Datanghe village. The main spawning ground for redlip loach were Huanzishu village to Luzhou south, Shibizi village to Lujiaoshu village, Guijiantan village to Yaodianzi village and Luolin Village to Erxi Village. The spawning behavior was significantly correlated with water temperature and water level. While the water flows velocity does not have significant impact on the spawning.5In this study,176specimens of elongate loach were collected from8sample sites and146specimens of redlip loach collected from4sample sites for the genetic structure analysis. With the utilization of mitochondrial DNA analysis,25and36variable sites,25and39haplotypes of elongate loach and redlip loach were detected by Cyt b gene sequences, and haplotype diversity(Hd) were0.60852and0.87008, nucleotide diversity (π) were0.00089and0.00337, respectively.50and 56variable sites,44and55haplotypes of elongate loach and redlip loach were detected from control region gene sequences, and haplotype diversity (Ha) were0.90709and0.97253, nucleotide diversity (π) were0.00315and0.00689, respectively. The results showed that the genetic diversity of redlip loach was higher than elongate loach. Haplotype network structure and NJ molecular phylogenetic tree of both two fishes were not sharp branch or geographic populations. Hierarchical analysis of molecular variance (AMOVA) of Cyt b and control region gene sequence among and within populations revealed no significant genetic structuring among populations and variation were mainly within the population. Also, there was no significant population structure (Fst<0.05), and estimates of gene flows among groups were relatively high(Nm>1). Significant values of Tajima’s D, Fu and Li’s D*and Fu and Li’s F*, together with uni-modal mismatch distribution indicated that elongate loach had experienced recent demographic expansion, but the redlip loach had not clear experienced recent demographic expansion. |
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