ScienceAsia 24 (1998): 021-036 |doi: 10.2306/scienceasia1513-1874.1998.24.021

ELECTROPHORETIC AND MORPHOMETRIC ANALYSES IN, SPECIES DIFFERENTIATION OF SMALL OYSTERS, SACCOSTREA SPP., IN THAILAND

PORNSAWAN VISOOTIVISETH^a, AMANDA DAY^b AND TAWEERATANA SIWADUNE^a

ABSTRACT: Small oysters, Saccostrea spp., were collected from different locations in Thailand including Ko Chang-Trat ,Sri Racha-Chonburi, Samsaeb and Ko Talu-Chumporn, Ko Prab-Surat Thani, Tubtieng-Trang, and Ko Kaoyai-Satul. These oysuirs possessed chomata and were identified as species "A" "B" or "C" by electrophoresis. All shells were subjected to morphometric analyses except those damaged by their removal from the substrate and possible hybrids: The following dimensions were measured for each shell: dorso-ventral and antero-posterior measurements, valve thickness, overall thickness, depth of umbonal cavity, length of hinge plate, and width of adductor muscle scar. Observations of position and colour of the scar, and arrangement of chomata were also made. These parameters, in addition to 3 parameters of index of shell shape, were subjected to 2 methods of statistical analyses using the SPSS statistical computer package. The first method was the analysis of variance and Scheffe's test. Relative similarities of the populations based on gene frequencies and mbrphometric analysis were constructed by UPGMA program. The results of both techniques correspond with each other very well. Thus the result of morphometric analysis of oyster shells can be used in species differentiation of oysters. Another statistical method attempted was discriminant analysis. This technique was investigated to obtain the percentage of samples classified correctly and to see whether it was possible to reduce the number of morphological factors for the determination of oyster species by shell morphometric analysis. The stepwise selection procedure showed that morphological factors could be reduced to only 8 factors. The average values and standard deviations of each factor within species A Band C are presented. The overall percentage of samples classified correctly in each species was 91.05% as compared to the electrophoretic results.

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a Faculty of Science, Mahidol University, Rama VI Rd. , Phyathai, Bangkok.
b Plymouth Marine Laboratory, Prospect Place, Plymouth.

Received November 1, 1997