Evseenko et al.: New data on the morphology of 7yphlachirus elongatus 119 
lateral line (loading is 0.9964), and the 
PC2 is associated with the number of rays 
in the dorsal and anal fins (loadings were 
0.7963 and 0.5990, respectively) (Table 3). 
The PC1 and PC2 describe 96.1% of the 
data spread (80.6% and 15.5%, respec- 
tively). Individuals of T: lipophthalmus 
and T: caecus did not form separate clouds 
of points but found themselves on the 
periphery of the cloud for T: elongatus in 
the area of higher PC1 values. 
We did not find linear correlations 
between body length and any other mor- 
phological characters: Spearman’s rank 
correlation coefficients did not signifi- 
cantly differ from zero in all the cases. 
The Pearson’s correlation coefficients 
Figure 4 were the same—all coefficients were zero. 
Photographs of the pectoral fin of a Mekong blind sole (Typhlachirus elon- 
gatus), 71 mm in standard body length, caught on May 2010 in the Mekong 
River delta of Vietnam, showing (A) the right (ocular) side of the body and 
(B) the left (blind) side of the body after staining with alizarin. The arrow in 
panel A points to the fin. 
Molecular analysis 
Seven haplotypes of the mtDNA CO1 
gene were found in species of Typhlachi- 
rus from the Mekong River delta, with 
absent. In the areas where fish were caught in the Mekong 
River, waters in the bottom layer had temperatures of 
28.2-34.1°C and salinity of 0.05—21.0. The early stages of 
development of this species are unknown, but metamor- 
phosis and sinking to the bottom occur early—the smallest 
specimens found in collections of fish caught with trawl 
gear reached a size of 14 mm SL. Our new collections indi- 
cate that the species is quite numerous. 
Distribution 
Typhlachirus elongatus has been found in the estuarine 
part of the Mekong River (Pellegrin and Chevey, 1940; 
Evseenko and Bolshakov, 2018). Blind sole were detected 
in both of the main rivers of the Mekong River delta, the 
Co Chien (Mekong) and Hau (Bassak) Rivers (Fig. 1). 
Statistical analysis 
Results of the analysis of the combined sample (based on 
data from our work and from previous studies for all 3 spe- 
cies of Typhlachirus) reveal that all the characters, except 
the number of pores in the lateral line, have distributions 
different from normal. In this regard, we used medians 
and interquartile ranges to describe the average values of 
diagnostic features and the spread of data, respectively 
(Table 2). The results of principal component analysis indi- 
cate the homogeneity of the studied sample of specimens. 
The individuals form a single homogeneous group in the 
space of the first 2 principal components (PCs) (Fig. 5) that 
is centered around the zero coordinates. The PC1 is almost 
exclusively associated with the number of pores in the 
Table 2 
Means, minimums (Min), maximums (Max), medians 
(Med), and lower interquartile (LQ) and upper interquartile 
(UQ) ranges of meristic characters and body proportions 
for the sample of 3 species of the genus Typhlachirus that 
combines data for specimens collected from the Mekong 
River delta in 2018 and for specimens described in litera- 
ture (Chabanaud, 1948; Hardenberg, 1931a; Pellegrin and 
Chevey, 1940; Tan and Grinang, 2020). Features include 
number of rays in dorsal fin (D), number of rays in anal 
fin (A), number of rays in caudal fin (C), number of rays 
in pectoral fin on the ocular (right) side of the body (P1,) 
and on the blind (left) side (P1,), number of pored scales 
on the horizontal branch of the ocular side lateral line not 
including scales on caudal fin (LL), number of precaudal 
vertebrae (PrCV), number of caudal vertebrae (CV), num- 
ber of vertebrae (V), body depth at pectoral fin base (BD), 
and head length (HL). n=the number of specimens used in 
the analysis. 
Character Mean Min—Max LQ—Med-UQ 
49-51-52 
35-36-38 
12-12-12 
1-1-2 
4-4-5 
92-95-99 
9-9-9 
24-25-25 
33-34-34 
41-43-44 
23-24-25 
