3.2 Elasmobranchii (Sharks and rays)
A total of 52 samples were sequenced belonging to 5 order, 8 families,
13 genera and 21 species (Table 1). Among these 21 species, two species
have been found as endangered (EN), five as vulnerable (VU) and seven as
near threatened (NT). One species was least concern (LC), two were not
evaluated (NE) and the remaining four species were data deficient (DD)
(IUCN, 2020).Chiloscylliumburmensis andC. hasseltiiwere reported as two new records (Ahmed et al., 2019b) in this area. The
sequence analysis indicated the average nucleotide frequencies to be- A:
25.90%, T:32.70%, G:16.20% and C:25.20%. The base composition
analysis for the COI sequence showed that the average percent T content
was the highest and the average percent G content was the lowest; the AT
content (58.60%) was higher than the GC content (41.40%). The GC
contents at the first, second and third codon positions for the
Elasmobranchii were 53.30%, 43.60% and 27.70%, respectively. At the
first codon position, the usage of T (20.00%) was the lowest, and the
usages of the other bases were 23.50%, 27.40% and 29.50% for C, A and
G respectively. At the second codon position, the content of T (42.00%)
was highest, and the percentage of the other bases were 29.40%, 14.50%
and 14.20% for C, A and G respectively. At the third codon position,
the base usage was T: 37.00%, C: 22.80%, A: 35.70% and G: 4.90%; the
G content being the lowest, exhibited a clear pattern of anti-G bias.
The K2P genetic distances within each taxonomic level are summarized in
Table 2. The average genetic distance within species, genus, family and
order were 1.2±0.0007%, 6.07±0.014%, 11.08±0.018% and 14.68±0.04%,
respectively. The NJ tree clearly distinguished all the species and the
species belonging to 8 families were represented by eight distinct
clades (Fig. 1).