There have been reported around 11 aquatic invasive alien species (IAS) found in Malaysian waters. Cherax quadricarinatus, or commonly known as Australian redclaw crayfish, is one of the invasive species. C. quadricarinatus has the potential of causing negative impacts ecologically and economically in the local environment as it has reported in several countries if they get established and not monitored properly. Habitat alteration, native species depletion and spreading of diseases are among the reported negative impacts of C. quadricarinatus. This study was conducted with the aim to assess the genetic diversity of C. quadricarinatus from 4 different populations. Uncovering the diversity and population structure of the redclaw crayfish will help in enhancing the understanding of adaptation and survival of C. quadricarinatus. Thus, the information can be used in monitoring and management of this invasive crayfish in future. DNA of C. quadricarinatus was successfully extracted from its tissue and amplified via polymerase chain reaction (PCR) using mitochondrial DNA (mtDNA) 16S gene then proceeded for sequencing and analysed using several genetic analysis software to understand the diversity, phylogeny and population structure of this invasive crayfish species. A total of 493 bp fragments of 32 samples from four sampling sites were obtained. Four haplotypes were observed which Hap-1 was the most common haplotype. The highest genetic variation is Selangor (Pi = 0.00248, Hd = 0.694). However, low levels of both haplotype and nucleotide diversity indicates the loss of genetic diversity. Analysis of molecular variance (AMOVA) results revealed that the percentage of genetic variation within the population was 69.58% while among populations was 30.42%, indicating significant genetic differentiation among population (P < 0.05). The maximum likelihood tree showed that all haplotypes were clustered and grouped together with United States, Czech Republic, China and Australia.

Freshwater invasive alien species (IAS) are non-native organisms that were intentionally or unintentionally released into local water bodies and later harmed the invaded habitat by disrupting the ecological processes. Over the last few years, environmental deoxyribonucleic acid (eDNA) analyses have been used in many studies to detect IAS, with positive results. However, with the help of geographic information systems (GIS), efforts to detect the presence of IAS can be made faster and more efficiently. In this paper, we review the background of IAS in Southeast Asia and management efforts undertaken involving the input of known habitat-specific geographical parameters into GIS mapping. Via this strategy, it is possible to identify and distinguish areas that fit IAS habitat features from those that do not. eDNA analysis can later be applied to confirm the presence of IAS in detected areas, enabling further studies and actions. The presence of IAS in certain areas can be used as an indicator to assess the environmental integrity of native waterways. This combined method is likely the first approach to be applied to the detection of freshwater IAS in local water bodies. Apart from saving energy and resources, embedding GIS and eDNA into the study of IAS not only benefits the ecosystem but also assists locals and authorities in managing and taking necessary enforcement actions to curb further spread.

The redclaw crayfish had been listed as an invasive species in Malaysia following the various negative impacts displayed on both environment and economy. The species are largely culture in Malaysia for food, but unluckily escaped and expands to several waterbodies across the country. For effective control management of redclaw crayfish species, a total of 52 wild samples were collected from six locations in Peninsular Malaysia and analyzed using a 16S mitochondrial DNA to assess their genetic diversity and introduction history. Five haplotypes were detected associated with an overall low genetic diversity (Hd = 0.385, π = 0.00133). A single genetic structure was detected with a phylogenetic relationship showing two clusters related to the haplotypes from Australia and Papua New Guinea. The finding of this study provides the basic data that will aid the appropriate Malaysian authorities for both monitoring and management strategies of redclaw crayfish in Peninsular Malaysia.

The introduction of invasive Cichla spp. was followed by the several reports regarding the decline of local freshwater native species in Malaysia. The purpose of this research was to generate information concerning the introduction history of Cichla spp. in Malaysia. Studies on genetic diversity and structure provides the essential baseline data for monitoring and conservation of invasive species. This will help to clearly understand the propagule pressure and genetic distribution of Cichla spp. in the invaded freshwaters of Malaysia. A total of 61 samples of Cichla spp. were collected from 9 sampling location in Malaysia for mitochondrial DNA (control region) analysis. Overall samples showed high genetic diversity (Hd, 0.6700; π, 0.0254) and yielded 9 haplotypes resulted from different Cichla spp. present. The maximum likelihood tree with strong bootstrap support revealed that Cichla spp. forms 3 clusters, and confirmed to be C. monocoulus, C. occelaris and C. temensis. Except for Malacca populations, other populations were largely dominated by either C. monocoulus or C. occelaris. The current study suggesting that more than one introduction event of invasive Cichla spp. occurred in Malaysia. HIGHLIGHTS One of the common problem in the conservation effort for Malaysia’s freshwater aquatic ecosystem is failure to understand the introduction events of invasive species (Cichla) Mitochondrial DNA analysis (control region) conducted in order to find the genetic diversity and genetic structure of invasive Cichla across freshwater habitats in Malaysia High genetic diversity was observed, suggesting multiple introduction occurance of invasive Cichla in the country GRAPHICAL ABSTRACT

Cherax quadricarinatus (von Martens, 1868) is a highly invasive species that is resilient and highly adaptable to environmental conditions in new locations. Its presence brings along ecosystem imbalances and causes socioeconomic losses in invaded areas. Due to the destructive behaviour, it is important to conduct preliminary assessment methods and scientific studies especially on its behavioural and dispersal patterns. Thus, this study aims to determine the habitat distribution patterns of C. quadricarinatusbased on the methods of GIS and environmental DNA (eDNA) analysis. The study was done at Felda Tenang, Terengganu, Malaysia. Based on the geographical features and climate conditions of the study area, we theorized that there are fewer and older C. quadricarinatuspresent at higher areas but more and younger C. quadricarinatus at lower areas. We found that 91.67% of the study area to be invaded, thus imploring the need for future mitigation plans to curb their dispersal into new areas. Future studies should also be done to determine the habitat distribution patterns of C. quadricarinatus in other areas.