Lao PDR, a landlocked country in the lower Mekong River basin of Southeast Asia, has been considered a global biodiversity hotspot with a high level of biological endemism. In recent years, urban development and industrialization have affected the water quality of freshwater ecosystems in Lao PDR. However, the assessment of water quality in the country is primarily focused on a physicochemical method, while the application of a multimetric index (MMI) approach using benthic macroinvertebrates for biomonitoring in rivers and streams has not been established. MMI, based on benthic macroinvertebrates, is a biomonitoring tool that considers the effects of multiple anthropogenic impacts on benthic macroinvertebrate metrics associated with their biological attributes (e.g., taxa richness, composition, pollution tolerance, habits, and functional feeding) and aggregates individual metrics into a single value for assessing the water quality and health conditions of aquatic ecosystems. Here, we developed an MMI based on macroinvertebrate communities collected during 2016–2018 from 10 localities of streams and wadeable rivers in Lao PDR. Of the 54 potential metrics tested, 35 candidate macroinvertebrate metrics representing richness, composition, trophic structure, habit, and tolerance to pollution were selected, while 19 metrics were excluded. Of the 35-candidate metrics, a total of 11 core metrics (Total taxa, EPT taxa, Ephemeroptera taxa, %Diptera, %Plecoptera, %Tolerant, Beck’s biotic index, %Intolerant, Filterers taxa, %Sprawlers, and %Burrowers) were finally selected for the development of MMI based on their sensitivity, redundancy, and easy-to-apply tool for the biomonitoring program. These metrics can be used to distinguish the reference (seven sites) from stressed conditions (seven sites). In addition, the final MMI scores classified 40 sampling sites into four classes of water quality, including excellent (25%), good (10%), fair (60%), and poor (5%), which the conventional physicochemical method could not clearly distinguish. The Lao MMI developed in this study is an effective tool for evaluating the water conditions of sites affected by human activities, particularly agricultural areas, and, thus, is appropriate for use in future studies for assessing the ecological conditions of rivers and streams in the Mekong region.

The anti-oomycetic effects of sodium chloride and potassium permanganate on the vegetative and zoosporic stages of Achlya sp. BKKU 0502, Saprolegnia diclina BKKU 0506, Aphanomyces sp. BKKU 0508, Achlya ambisexualis BKKU 0615 and Achlya bisexualis BKKU 0616 were investigated at 25°C. The results showed that the exposure of the samples to 3.0 and 2.5% sodium chloride for 24 h was toxic to the vegetative and zoosporic stages, respectively. Moreover, 200 and 25 ppm of potassium permanganate were effective at killing the vegetative stage at 24 h and the zoosporic stage at 1 h, respectively. The toxicities of 2.0, 2.5 and 3.0% sodium chloride for controlling oomycete activity were determined using tilapia (Oreochromis niloticus) eyed eggs for both 1 and 24 h treatments. The results showed that salt concentrations at levels of 2.0% or higher reduced the hatching rate percentage of the treatment groups to a value significantly different from that of the control group (P<0.05). A noteworthy result was that the 3.0% sodium chloride treatment for 24 h produced a 0% hatching rate. The treatment of the eyed eggs with 100, 150 and 200 ppm potassium permanganate to control the oomycete activity had a highly toxic effect on the eggs: the results showed a 0% hatching rate for all of the treatment groups after 1 and 24 h exposures. Therefore, it is not possible to use sodium chloride or potassium permanganate to prevent the activity of oomycetes on tilapia eggs because these two chemicals decrease the hatching rate. Other chemicals that may be safe to use on other edible aquatic organisms will require further investigation. Key words: Sodium chloride, potassium permanganate, oomycete zoosporic stage, vegetative stage, tilapia eyed eggs.

The micromorphology and histology of anuran skin, particularly in Thai species, remain relatively understudied. Anurans use their tongues for prey capture and their hands and feet for adhesion and mating, suggesting a close relationship between micro-surface features and histological structure. Information on Sylvirana nigrovittata is particularly limited. This study provides a detailed examination of the micro-surface and histological characteristics of the tongue, fingers, toes, nuptial pad, and humeral gland in S. nigrovittata. Specimens collected from Phu Luang Wildlife Sanctuary in Loei province, northeastern Thailand, were studied using scanning electron microscopy (SEM) for micro-surface features and H&E staining for histological details. SEM micrographs revealed that the tongue was cordate-shaped, with about 75% of its surface covered by filiform papillae and 25% by fungiform papillae housing taste buds. Filiform papillae were trapezoidal, averaging 23.88±5.68 µm in width and 38.83±6.57 µm in length, while fungiform papillae were disc-like, averaging 52.95±14.64 µm in width and 66.70±15.88 µm in length. Digital pads on fingers and toes presented prismatic cells, with fingertip cells averaging 7.09±0.97 µm in width and 11.81±1.24 µm in length, and toe cells averaging 8.40±1.37 µm in width and 11.28±1.63 µm in length. Subdigital surfaces were smoother, containing squamous cells with dimensions of 10.65±3.21 µm in width and 21.29±4.35 µm in length. Subarticular tubercles were composed of prismatic cells with hexagonal or pentagonal surfaces, averaging 10.02±2.85 µm in width and 13.08±1.94 µm in length. Nuptial pad displayed cylindrical structures with dome-like tips, averaging 24.01±3.96 µm in width and 21.16±4.37 µm in length, and feature mucous openings. They consisted of a thick keratinized stratified squamous epithelium and a dense dermis with specialized mucous glands. Humeral gland exhibited rough surfaces with squamous cells and microridges, showing both small and large mucous openings, with average cell dimensions of 16.23±1.70 µm in width and 19.11±2.05 µm in length. Histological analysis confirmed that these structures were predominantly composed of keratinized stratified squamous epithelium, with variations in dermal collagen density and mucous gland distribution. This study enhances our understanding of the skin and gland morphology in S. nigrovittata, highlighting on its anatomical and functional adaptations.