Morphometric identification of mud crabs of the genus Scylla available in Bangladesh waters

Abstract

There has been a lot of ambiguity in taxonomy of mud crab species of the genus
Scylla. In order to identify and ascertain the number of species of genus Scylla available in
Bangladesh waters, a total of 84 specimens were collected from five different coastal locations.
Based on the morphometric analysis, the specimens were divided into three Morphotypes. The
average carapace width of Morphotype 1, Morphotype 2, Morphotype 3 were 100.7±30.4,
113.3±21.3 and 95.6±17.3, respectively. On the other hand, in case of morphometric
measurements, except two measurements (PD/PL, PL/ICW), 25 measurements out of 27
measurements such as LSH/ICW, CW/8CW, CL/ICW, PWC/ICW, FW/ICW, PWC/FW,
FMSH/FW, FMSH/DFMS, DFLS/FW, DFLS/FW, DFMS/DFLS, SW/ICW, AW/SW, DL/PL,
PW/PL, (PW*PD*0.7854)/PL, IPS/PL, OPS/PL OPS/PL, IPS/OPS, ICS/PL, OCS/PL,
ICS/OCS, ML/PL, 5PW/5PL and 3 PML/ICW ratios were found to be significant at various
level (p<0.001, p<0.01, and p<0.05). The variables were obtained via discriminant function
analysis. The first three principal components (PC) accounted for 55.865% of the total variance
(29.712% for PCI, 14.764% for PCII and 11.390% for PCIII). Component I contained ML/PL,
FMSH/DFMS, DFMS/FW, LSH/ICW, DFLS/FW, PW/PL, CW/8CW and
(PW*PD*0.7854)/PL; component II contained FW/ICW and IPS/OPS; component III contained
IPS/PL, OPS/PL and 5PW/5PL. Sample centroids of discriminant function scores 100% of
Morphotype 1 sample, 100% of Morphotype 2 sample, 100% of Morphotype 3 sample, 100% of
Morphotype 4 sample and 100% of Morphotype 5 sample were correctly classified. In
conclusion,three morphotypes identified resembling to three mud crab species such as S. serrate,
S. olivacea and S. paramamosain. However, reliable molecular analysis can confirm if they are
different species or the morphotypes are due to morphological plasticity.