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Telemetry is an emerging method to study fish ecology and a reliable tool that provides useful information for managing and conserving aquatic fauna and river habitats. However, the reliability of telemetry depends on several technical factors. Implantation of the acoustic transmitter is one of the major aspects that ensure the survivability of the animal subject when released into the wild. Studies on the technicalities involving telemetry methods are limited; therefore, this study investigated the surgical insertion of an acoustic transmitter into the peritoneal cavity of Channa lucius and Neolissochilus soroides or locally known as Bujuk and Tengas. A severity index was used to rate the appearance of surgical wounds observed on the day of release into the river. Fish mortality and complications such as bleeding were not observed in both species post-surgery. The progress and prognosis of wound healing of C. lucius were better compared to N. soroides, with generally lesser inflammation and more sutures shed. Despite visually severe inflammation on N. soroides on day-12 and day-19 post-surgery, there was a good indication that skin integuments were healing. This data suggests that C. lucius has faster wound healing abilities compared to N. soroides. All fishes implanted with the acoustic telemetry method survived up to 244 days upon release into the Tembat River, Hulu Terengganu, Malaysia, and retained the tag throughout the tracking period.

The distribution of the phytoplankton community in different locations of Puah Reservoir, Malaysia was investigated from May to December 2019 to examine the phytoplankton compositions and density. Seven sampling locations were selected namely Terengganu Mati (P1), Limbing Besar (P2), Temba Outlet (P3), Pela-gong (P4), Sireh (P5), Centre Dam (P6) and Power Intake (P7). A total of 543 cell/mL were recorded from 35 genera in the reservoir. These identified species belonged to six major plankton groups: 12 green algae (35.29%), nine blue-green algae (26.47%), nine diatom (23.53%), two golden algae (5.88%), two filamentous (5.88%) and one flagellate (2.94%). During this period, Chlorophyta was the most abundant group (40% of the total phytoplankton), followed by Bacillariophyceae (29%), Pyrrhophyta (19%), Cyanophyta (12%) and Chrysophyceae (1%). The highest composition of phytoplankton was recorded at P7 (32%), followed by P3 (16%), P1 (14%) and P4 and P2 with the lowest (8% and 7%), respectively. The lowest density was observed during dry season (162 cell/mL) and high density during wet season (412 cell/mL). Species richness was discreetly greater in the wet season however, evenness index was ≥0.8, thereby indicating a similarity in species abundance. The water temperature, pH and dissolved oxygen correlate positively with phytoplankton at P = 0.01. The overall mean values of temperature for wet and dry season were 29.3 ± 1.79 °C and 27.5 ± 1.55 °C while dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solid (TSS) were 16.2 mg/L and 4.7 mg/L, 3.4 mg/L and 2.9 mg/L, 15.2 mg/L and 12.7 mg/L, and 0.5 mg/L and 2.3 mg/L, respectively. Water transparency, pH and DO were found to be important factors characterising each sampling location.

The tire track eel, Mastacembelus favus, is an economically important freshwater fish in mainland Southeast Asia. Understanding the spatial population structure is important to design an effective and efficient management of the species. The aim of this study was to investigate the genetic diversity and structure of M. favus populations. In total, 519 individuals from 30 locations across its distribution range were genotyped using a set of eight polymorphic microsatellite loci. Results showed that populations in Mekong and Chao Phraya exhibited higher genetic variability than those from Gulf of Thailand and Malay–Thai Peninsula. Clustering results revealed two evolutionarily isolated groups geographically separated at Northeastern Cambodia; the more widespread group was further divided into two subclusters. The spatial genetic variation and structure of its populations are attributed to the evolutionary history and population dynamics of the species. The study provides important information for the management and conservation of M. favus in Southeast Asia.

An investigation study was conducted in Bukit Merah Reservoir (BMR) for the assessment of arsenic concentration in the surface sediment in 23 sampling stations. The sediment samples were digested and analysed for arsenic using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Sediment parameters such as pH (4.42 ± 0.71), redox potential (121.77 ± 42.45 mV), conductivity (205.7 ± 64.07 μS cm–1) and organic matter (25.35 ± 9.34%) were also examined. The main objectives of this study are to determine the arsenic distribution and concentration and at the same time to assess the enrichment of arsenic using the geoaccumulation index (Igeo) and enrichment factor (EF). This study shows the total arsenic concentration in the surface sediment of BMR is 4.302 ± 2.43 mg kg–1 and found to be below the threshold value of Canadian Interim Sediment Quality Guidelines (ISQG). High arsenic concentration is recorded near the southern part of the lake where anthropogenic activities are prevalent. Based on Igeo, 13% of sampling stations are categorised as moderately polluted, 52.2% as unpolluted to moderately polluted and the rest is categorised as unpolluted. EF shows 78.3% stations are classified as extremely high enrichment and the rest as very high enrichment. This finding provides important information on the status of arsenic contamination in BMR and creating awareness concerning the conservation and management of the reservoir in the future.

The drastic changes in hydroelectric reservoir development created a completely new ecosystem that affects the river, particularly in the inundated area. In this study, five Neolissochilus soroides and Channa lucius were surgically implanted with a unique coded acoustic transmitter to observe the habitat utilisation and movement activity in Tembat Reservoir after the inundation process. All of the individuals were released into the transition zone of the reservoir and observed using passive and active acoustic tracking devices from April to December 2018. Kruskal-Walis test showed no significant difference between the average size of core area for N. soroides and C. lucius, x2(1) = 1.320, p = 0.251. The home range also showed a similar result for N. soroides and C. lucius where there was an insignificant difference, x2(1) = 0.273, p = 0.602. However, duration wise, N. soroides spend more time in the transition zone, R1 (M = 2.71 hrs, SE = 0.38), and C. lucius in the riverine zone, R5 (M = 7.14 hrs, SE = 6.13) and R6 (M = 3.85 hours, SE = 6.36). From the active tracking survey, PCA identified three (62.32%) and four (71.19%) components with eigenvalues greater than 1 for N. soroides and C. lucius, respectively. Three most important habitat parameters for N. soroides were the size of river (r = 0.97), existence of canopy cover (r = 0.77), and substrate type (r = 0.79).While, for C. lucius were mesohabitat type (r = 0.79), distance to riffle (r = 0.97), existence of canopy cover (r = 0.90), and elevation (r = 0.90). A 24-hour movement frequency analysis for both species revealed two active hours of movement at dusk and dawn for both species. From the study, it is known that N. soroides and C. lucius respond differently towards the inundation of the reservoir. The findings in this study can be implemented for effective aquatic management and conservation plan to ensure sustainable dam development.

Instream barriers such as waterfalls and man-made dams may result in distinct fish assemblages on both sides of the barriers. To determine the influence of these barriers on fish assemblages, a study was conducted in Sungai Enam that have substantial barriers including an 18-m high waterfall with 6.1% slope. Fish were captured using a backpack electrofishing gear together with scoop nets. Thirteen fish species from six families were recorded along this stream, but only Poropuntius smedleyi (Cyprinidae) can be found along the stream and the reach above the waterfall. Studies on a second site, Sungai Kooi, that has a 65m high and 90° slope waterfall, revealed eight fish species from three families, but only P. smedleyi and Devario regina (Cyprinidae) occurred above the waterfall. The number of species in both streams increases from upstream to downstream. A chi-square test revealed that the total number of species among reaches in Sungai Enam differed significantly. Fish species found above the waterfall are known to have no special adaptations to climb or jump over the barriers. Therefore, to explain their existence above the substantial waterfalls especially in Sungai Kooi, we proposed three hypotheses: (1) the world was once flooded and there was no limitation to fish distribution, (2) fish species assemblages were separated by land uplifting, and (3) there are other stream branches enabling fish movement into respective streams. Further studies are required to confirm these hypotheses.

In this paper, we studied some biological aspects of big eye scad (Selar crumenophthalmus) from Maldives. The fish sample was collected from the local fish market at Bangaa Faru, Male, Maldives. The length of the samples were ranged from 7.7 cm to 24.5 cm (mean value = 16.85 ± 2.82 cm) in fork length. Body weight ranged between 8 g to 255.6 g (mean value = 87.76 ± 40.41 g). The exponent values (b slope) of lengthweight relationship of S. crumenophthalmus are 2.9838 for females and 2.7687 for males; indicating negative allometric growth pattern for both sexes. Synchronous reproductive behaviour was observed in both sexes and a pronounced peak of Gonadosomatic index was observed in females in January 2013. It is estimated that length at first maturity (L50) for females is at 19.39 cm FL and for males at 21.76 cm FL. Our result also suggest that big eye scad have a reduced swimming capability, resulting the species to be easily caught. Careful planning and management should be implemented to prevent the big eye scad from being overfished.

The importance of terrestrial insects as food items for freshwater fish was studied by examining stomach contents of Devario regina (Fowler 1934) and its population parameters at canopied areas of selected tributaries of Sungai Kerian, in the northern state of Peninsular Malaysia. Ninety six percent (121 out of 126) of the fish stomachs examined contained food materials in the stomachs and the values of percentage of occurrence (%F), percentage numerical (%N) and percentage points (%P) indicated that collected fish ate similar food items in all rivers. Among the food categories, scavenging terrestrial ants (Formicidae) were the most dominant food item, hence the main diet for this species. The Index of Relative Importance (IRI) scores of food items indicated that ants were higher than other food items. This surface water feeder experienced a positive allometric growth (W = aLb) with a b (rate of growth) value of 3.256. Its asymptotic length, growth constant and growth performance index represented this species with a short life-span (L∞ = 10.90 cm, K = 1.20 year-1, φ’ = 2.15, tmax = 3 year, respectively) and had higher natural mortality (M = 2.40 year-1) than fishing mortality (F = 0.35 year-1) while the fish stock was underexploited (E = 0.13). The finding of this study indicated the importance of terrestrial ants as a food source that support excellent growth of D. regina and the need to conserve riparian trees along river banks to provide allocthonous materials and habitats for the ants.

Water quality profile of Pergau Reservoir or also known as Sultan Ismail Petra Hydroelectric Reservoir has been conducted from 28th October to 3rd November 2019 during Pergau scientific expedation 2019. Three (3) lentic sampling stations (P1, P2 and P3) were selected with eleven (11) water parameters such as water temperature, pH, biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solid (TSS), total dissolved solid (TDS), dissolved oxygen (DO), turbidity, ammonical-nitrogen, oil and grease (O&G), and total coliform were analyzed for water quality status of Pergau Lake. Stratification profile of DO, pH and water temperature were recorded by 10m depth at all lentic stations. Generally DO, temperature and pH reading at the surface lentic sampling stations ranging between 7.11 to 9.21 mg/L, 27 to 27.5 °C and 7.50 to 8.72, respectively. Anoxic layer was detected at depth of 9 m at P1 whereas 3 m at P2 and P3. Profiling of DO, pH and water temperature shown decreased pattern when the water depth increased. Others parameters such as COD at the subsurface were ranged from 1.3 to 1.4 mg/L, TSS reading recorded ranged from 4.00 to 6.80 mg/L, ammoniacal-nitrogen ranged from 0.05 to 0.07 mg/L whereas BOD5 were ranged from 1.3 to 1.4 mg/L. The Department of Environment – Water Quality Index (DOE-WQI) classification was used to assess the water quality status of the selected sampling locations. The results showed that all locations fall under Class I ranged between 92.66 to 94.55% and in summary the area can be classified as clean and suitable for sensitive aquatic organisms.

Gracilaria red algae are notable for their economic importance as agrophytes, sold as salad vegetable, and used as the base for selected food and nonalcoholic beverages. A wild population of Gracilaria exists in coastal areas of Sarawak, Malaysian Borneo, but there is only limited knowledge on species diversity and its abundance leaving the untapped economic potential of this resource. This study was carried out to determine diversity of wild Gracilaria populations in Lawas, Santubong, and Asajaya, Sarawak, using the combination of morphological character examination and 5′ region of the mitochondrial cytochrome c oxidase 1 (CO1-5P) gene analysis. Identification of the species using morphological characters revealed three species, namely, Gracilaria changii, G. blodgettii, and G. arcuata, had been collected from the sampling sites. However, based on 672 bp CO1-5P gene sequence analysis, all the three species were identified as G. blodgettii; besides, low genetic divergence values (0.17%–0.34%) were scored between samples in this study with the same species in GenBank. In the phylogenetic trees, all samples in this study group together with other G. blodgettii have high bootstrap values; thus, this species is monophyletic. This study implies that species identification of Gracilaria and other seagrass taxa which have a phenotypic plasticity problem should include the CO1-5P gene analysis as it is a reliable gene marker for species diversity assessment.

Gracilaria red algae are notable for their economic importance as agrophytes, sold as salad vegetable, and used as the base for selected food and nonalcoholic beverages. A wild population of Gracilaria exists in coastal areas of Sarawak, Malaysian Borneo, but there is only limited knowledge on species diversity and its abundance leaving the untapped economic potential of this resource. This study was carried out to determine diversity of wild Gracilaria populations in Lawas, Santubong, and Asajaya, Sarawak, using the combination of morphological character examination and 5′ region of the mitochondrial cytochrome c oxidase 1 (CO1-5P) gene analysis. Identification of the species using morphological characters revealed three species, namely, Gracilaria changii, G. blodgettii, and G. arcuata, had been collected from the sampling sites. However, based on 672 bp CO1-5P gene sequence analysis, all the three species were identified as G. blodgettii; besides, low genetic divergence values (0.17%–0.34%) were scored between samples in this study with the same species in GenBank. In the phylogenetic trees, all samples in this study group together with other G. blodgettii have high bootstrap values; thus, this species is monophyletic. This study implies that species identification of Gracilaria and other seagrass taxa which have a phenotypic plasticity problem should include the CO1-5P gene analysis as it is a reliable gene marker for species diversity assessment.

Red seaweed Gracilaria, one of the largest genus in Division Rhodophyta inhabits Sarawak coastal water. This study was designed to identify the species of Gracilaria using morphological approach and to assess selected water quality parameters in Gracilaria habitats. Three field samplings were carried out in Santubong and Asajaya, Sarawak from November 2013 to December 2014. Overall, three species were identified namely Gracilaria changii, G. blodgettii and G. coronopifolia, attached to net of cage culture in Santubong and root of mangrove trees in Asajaya. In addition, three different taxa of aquatic macroinvertebrates (polychaete, small crab, bivalve) and single species of red seaweed (Acanthophora sp.) were observed in Gracilaria assemblages. An estimate of 37% to 40% of the upper part of the cage net in Santubong was covered by seaweeds and only 16% to 20% in Asajaya’s mangrove. The study had provided better information on identification of Gracilaria and their habitat in Sarawak. Future work involving DNA barcoding of each species is in progress.

Although freshwater biomes cover less than 1% of the Earth's surface, they have disproportionate ecological significances. Attempts to study the taxonomy and function of freshwater microbiota are currently limited to samples collected from temperate lakes. In this study, we investigated samples from the photic and aphotic of an aquaculture site (disturbed) of Temengor Lake, a tropical lake in comparison with the undisturbed site of the lake using 16S rRNA amplicon and shotgun metagenomic approaches. Vertical changes in bacterial community composition and function of the Temengor Lake metagenomes were observed. The photic water layer of Temengor Lake was dominated by typical freshwater assemblages consisting of Proteobacteria, Actinobacteria, Bacteroidetes, Verrucomicrobia, and Cyanobacteria lineages. On the other hand, the aphotic water featured in addition to Proteobacteria, Bacteroidetes, Verrucomicrobia, and two more abundant bacterial phyla that are typically ubiquitous in anoxic habitats (Chloroflexi and Firmicutes). The aphotic zone of Temengor Lake exhibited genetic potential for nitrogen and sulfur metabolisms for which terminal electron acceptors other than oxygen are used in the reactions. The aphotic water of the disturbed site also showed an overrepresentation of genes associated with the metabolism of carbohydrates, likely driven by the enrichment of nutrient resulting from aquaculture activities at the site. The results presented in this study can serve as a basis for understanding the structure and functional capacity of the microbial communities in the photic and aphotic zones/water layers of tropical man-made lakes.

Fish from three major rivers namely Pengkalan Chepa, Kelantan, and Galas rivers in Kelantan, Malaysia was caught using gill-nets with separate mesh sizes of 1, 2, 3, and 4 inches, respectively. There were 170 fish collected from the PCR systems, which represented 18 families and 21 species (2008-2009). The most common fishes, based on total fish captured, were Ikan duri (Arius maculatus) and Puyu (Anabas testudineus). A total of 245 individual fish were collected from KR (2010-2012) which comprised of 7 families and 22 fish species with the highest number of individual fish (51) collected during this survey was the spotted catfish (Arius maculatus). A total of 562 fish specimens representing 12 families and 32 species were captured from riverine monitoring in the GR systems (2008-2010).

A study was conducted at five selected rivers around Bukit Merah Reservoir, Perak, Malaysia for eight weeks in order to determine the fish diversity and distribution. A total of 28 species comprised of 9 families were identified. The study depicted that there were significant changes to the fish composition when compared to previous study which had captured 36 species due to different areas covered and different types of sampling gear used between both studies.

Population Dynamics of Bigeye Scad, Selar crumenophthalmus in Bangaa Faru, Maldives Selar crumenophthalmus (bigeye scad) locally known as mushimas, is a widely distributed fish in Maldives. For the biological study, random samples of Selar crumenophthalmus (bigeye scad) were collected from September 2012 to February 2013. The samples were caught from Bangaa faru, in Male’ atoll, Maldives. A total of 1648 samples were collected, with their fork length ranging from 7.7 cm to 24.5 cm (16.85 ± 2.82 cm) and body weight ranging between 8g to 255.6 g (87.76 ± 40.41g). FiSAT software was used in estimating the population parameters.

Red seaweed Gracilaria sp. is known as ‘Janggut Duyong’ by the local people of Sarawak. This macroalgae iswell-distributed in both temperate and tropical seawaters. Gracilaria sp. could be processed to produce agar forindustrial purposes whereas some people consumed it directly and become part of their daily diet. In terms ofecology, Gracilaria sp. is one of primary producer in the seawater and its presence can form habitats to supportother aquatic organisms. Despite its socio-economic and ecological importance, little is known about Gracilariasp. in Sarawak. Hence, this study is designed to: (i) determine the diversity and abundance of Gracilaria in cageculture of Lawas, Sarawak (ii) assess the water quality of the cage culture area where Gracilaria is found and(iii) determine other aquatic organisms that found within Gracilaria population. Three field samplings had beenconducted from October 2013 to November 2014 at cage culture areas of Awat-Awat Village, Lawas, Sarawak.Only single species of Gracilaria was found namely Gracilaria arcuata. Besides G. arcuata, Acanthophora sp.and Padina sp. were also found but in small patches. In addition, five different groups of aquatic invertebrateswere observed namely tunicates, bivalves, polychaetes, small crabs and brittle stars. The selected water qualityparameters namely temperature, pH, dissolved oxygen, salinity, turbidity, total suspended solid, orthophosphate,silicate and chlorophyll a were significantly different (p= 0.000) during all the three field samplings except fornitrite (p= 0.588). However, the values recorded were within normal range of standard water quality for tropicalestuarine area. Since healthy population of Gracilaria could be easily found here, therefore this area has thepotential for future seaweed aquaculture.