Abstract:
In many countries, including Sri Lanka, freshwater prawn industry is mainly based on
Macrobrachium rosenbergii which is called as giant freshwater prawn. However, now there is a
growing interest in many Asian countries to use Macrobrachium malcolmsonii as a potential
candidate in aquaculture programs due to its high growth rate. In Sri Lanka, M. malcolmsonii has
been reported mainly from the estuaries of eastern part of the country. Although, the adults of two
species show a few morphological differences, the appearance of young individuals of both species
are identical. Therefore, in many occasions identification and separation of the above two species is
difficult. The aim of this study was to distinguish M. rosenbergii and M. malcolmsonii using
morphological and molecular data. Twenty one M. rosenbergii individuals from Nilwala River
estuary and twenty six M. malcolmsonii individuals from Gal Oya estuary were used in
morphometric analysis. After data were subjected to normality test, nine characteristics were used in
Decriminant Function Analysis. Among them seven characteristics were derived as contributors that
help in delineating two species which need to be confirmed using the results of heritability tests. To
determine the utility of Single Stranded Conformation Polymorphism (SSCP) method in
distinguishing M. rosenbergii and M. malcolmsonii, partially amplified mitochondrial 16S rRNA
gene regions for both species were sequenced. The derived sequence lengths of both DNA
fragments were approximately 430 bp to 440 bp and the estimated nucleotide difference between
sequences of two species was approximately 19 bp. Then, SSCP technique was carried out using the
same PCR product. However, the SSCP technique failed to differentiate DNA fragments derived
from 16S rRNA gene region for two freshwater prawn species M. rosenbergii and M. malcolmsonii.
This may be due to the formation of more stable and similar secondary structures for this gene
region. Further studies are suggested to conduct SSCP method using more variable gene regions.
