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catchments all had high abundance and species richness. Hierarchical clustering and 
Detrended Correspondence Analysis (DCA) indicated that three main groupings of 
sites existed, each with a distinct community of associated species. Further analysis 
by Canonical Correspondence Analysis (CCA) with 12 significant environmental 
variables showed that these groups were significantly associated with respective 
environmental variables (Cai et al., 2018). 
New records of native species 
The current survey recorded a native fish species new to Nee Soon freshwater swamp 
forest: Barbodes lateristriga. It was observed mostly in the middle swamps with 
moderate canopy coverage and deep, open stretches of water converging to large ponds. 
One semi-slug, Damayantia cf. simrothi is believed to be a new record for Singapore 
and was found at six sites in Nee Soon. Eighteen native species of odonates were new 
to Nee Soon freshwater swamp forest though most of them are widespread common 
species in Singapore and only found at the outskirts or in open parts of the study area, 
viz. Podolestes orientalis, Libellago lineata, Argriocnemis rubescens, Pseudagrion 
australiasiae, Pseudagrion micro cephalum, Copera marginipes, Onychargia 
atrocyana, Acisoma panorpoides, Crocothemis servilia, Lathrecista asiatica, 
Neurothemis fluctuans, Orthetrum sabina, Orthetrum luzonicum, Psedothemis jorina, 
Rhyothemis triangularis , Trithemis aurora, Trithemis festiva and Tyriobapta torrida. 
In addition, two specimens of the Blackwater mud snake Phytolopsis punctata were 
found at Mid 1 sub-catchment. This species presents a new record for Singapore and is 
currently only found in Nee Soon freshwater swamp forest (Tan et al., 2014; Thomas 
et al., 2014). 
Presence of introduced species 
Introduced species can have severe impacts on the native species, causing decline 
of population and possibly extinction. Through the course of this study, six 
species of introduced fish and one species of shrimp were recorded and all are 
common and widespread throughout Singapore. These species include Osteochilus 
vittatus, Parambassis siamensis, Poecilia sphenops, Puntigrus tetrazona, Rasbora 
borapetensis, Rhinogobius giurinus and Macrobrachium nipponense. Larson & Lim 
(2005) documented that Rhinogobius giurinus has been outcompeting the local species 
of freshwater goby, Pseudogobiopsis oligactis at locations where the two populations 
overlap, a result corroborated by this survey. The less acidic water in the outskirts 
could have encouraged propagation of introduced over native species. As the lower 
reach of Nee Soon stream is connected to the spillway of the Upper Seletar Reservoir 
it is subject to occasional flooding when excess water is released from the Reservoir. 
Such events might inadvertently introduce foreign aquatic species that reside in the 
water bodies of the reservoir and thus account for the introduced species found. 
With the discovery of introduced species, it is of great importance to implement 
preventive measures to reduce the possibility of alien species from being introduced. 
Possible mitigation procedures might include monitoring and physical removal of the 
introduced species on a regular basis, as well as the stepping up of existing enforcement 
