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Understanding factors driving diversity across biodiversity hotspots is critical for formulating conservation priorities in the face of ongoing and escalating environmental deterioration. While biodiversity hotspots encompass a small fraction of Earth's land surface, more than half the world's plants and two-thirds of terrestrial vertebrate species are endemic to these hotspots. Tropical Southeast (SE) Asia displays extraordinary species richness, encompassing four biodiversity hotspots, though disentangling multiple potential drivers of species richness is confounded by the region's dynamic geological and climatic history. Here, we use multilocus molecular genetic data from dense multispecies sampling of freshwater fishes across three biodiversity hotspots, to test the effect of Quaternary climate change and resulting drainage rearrangements on aquatic faunal diversification. While Cenozoic geological processes have clearly shaped evolutionary history in SE Asian halfbeak fishes, we show that paleo-drainage re-arrangements resulting from Quaternary climate change played a significant role in the spatiotemporal evolution of lowland aquatic taxa, and provide priorities for conservation efforts.

The Betta broodfish supply in Indonesia majorly comes from wild populations and fetches a higher price compared to hatchery cross-breeds, especially Betta rubra. This condition exerts pressure on the wild populations. Therefore, this study aims to examine the diversity, distribution, and conservation status of Betta fish species list in the study area. A total of 422 Betta fishes were collected from January 2019 to January 2021 from 19 of 59 sampling locations surveyed, consisting of four species, namely, Betta imbellis (TL: 14.09-31.98 mm; BW: 0.03-0.39 g), B. splendens (TL: 21.09-40.14 mm; BW: 0.05-0.70 g), B. rubra (TL: 11.35 to 47.80 mm; BW: 0.02-0.90 g), and B. dennisyongi (TL: 20.09-47.81 mm; BW: 0.07-0.91 g). There are four Betta species occurred in Aceh waters, namely B. dennisyongi, B. rubra, B. splendens, and B. imbellis. The results showed that B. dennisyongi was found at 8 sampling locations and had higher local distribution (13.56% LD) followed by B. rubra (8.47% LD), B. splendens (6.78% LD) and B. imbellis which had the lowest distribution and was only found in two locations (3.39% LD). Furthermore, field measurements (in situ) of water quality in the wild habitat showed temperature ranging from 23.7 to 31.9°C while pH ranged from 5.24 to 8.51. Based on the IUCN Redlist data, B. rubra is categorized as being critically endangered.

Genetic diversities in two cultured oyster species, Crassostrea iredalei (Faustino 1932) and Crassostrea belcheri (Sowerby 1871) were assessed using a 581-nucleotide fragment of the mtDNA cytochrome oxidase subunit 1 (CO1) gene. A total of 103 C. iredalei individuals and 120 C. belcheri from 12 populations were sampled along the coast of Malaysia. Trees of unique haplotype samples generated based on Neighbor-Joining (NJ) algorithm revealed that many individuals had been misidentified and did not cluster with their presumed species based on morphological identification. BLAST results of DNA sequences showed presence of previously unreported C. madrasensis in Peninsular Malaysian waters (98% maximum identity). The true identity of the Muar ( Crassostrea sp .) and Semporna ( Saccostrea sp. ) populations were unresolved by two BLAST search and showed less than 88% identity with other species in GenBank. Repeated analysis of these two populations using 487 bp of the mitochondrial 16S gene data showed only a maximum identity less than 97%. Hence, the identity of these specimens remains unclear. Evolutionary divergences within presumed species were 0.001–0.011 and 0.034–0.313 between species. Findings from this study have important implications for aquaculture, management and monitoring of cultured populations as well as conservation of wild oyster species in Malaysia.

Background Rasbora tawarensis is an endemic freshwater fish in Lake Laut Tawar, Aceh Province, Indonesia. Unfortunately, its status is regarded as critical endangered with populations decreasing in recent years. To date no information on the spawning activities of the fish are available. Therefore, this study provides a contribution to the knowledge on reproductive biology of R. tawarensis especially on spawning seasons as well as basic information for conservation of the species. Methods Monthly sampling was conducted from April 2008 to March 2009 by using selective gillnets. The gonadosomatic index, size composition and sex ratio were assessed. The gonadal development was evaluated based on macroscopic and microscopic examinations of the gonads. Results The gonadosomatic index (GSI) varied between 6.65 to 18.16 in female and 4.94 to 8.56 for male. GSI of the female R. tawarensis was higher in March, September and December indicating the onset of reproductive seasons, the GSI and oocyte size being directly correlated with gonadal development stages. Although, a greater proportion of mature male than female was detected during the study, the sex ratio showed that the overall number of female was higher than male. The ovaries had multiple oocyte size classes at every stage of gonadal development, thus R. tawarensis can be classified as a group synchronous spawner or a fractional multiple spawner. Conclusion The spawning seasons of R. tawarensis were three times a year and September being the peak of the reproductive season and the female was the predominant sex. This species is classified as a group synchronous spawner.

The present study documents the isolation of eight polymorphic microsatellite markers from the bighead catfish, Clarias macrocephalus and cross-amplification in two other catfish species. The number of alleles per locus in C. macrocephalus ranged from 2 to 21. The most polymorphic locus was NCm - G12 with 21 alleles while the least polymorphic locus was NCm - H2 with only two alleles. Locus NCm - F8 significantly deviated from Hardy–Weinberg equilibrium ( P value <0.05) after Bonferroni correction. Linkage disequilibrium was non-significant in all loci comparisons. The observed and expected heterozygosities varied from 0.033 to 0.967 and from 0.033 to 0.942, respectively. Mean polymorphic information content for the eight loci was 0.765. Cross-amplification was successfully performed with two other catfish species, C. batrachus and C. meladerma for all eight loci. Locus NCm - D8 was monomorphic in both species while NCm - F8 was monomorphic only in C. batrachus. These newly developed markers would be useful for better management and conservation of the economically important C. macrocephalus species.

There were three presumed form of Rasbora found in Lake Laut Tawar, i.e. Depik, Eas and Relo. However, their phylogenetic status was remaining unclear. For this purposes the genetic data were utilized to resolve the taxonomic ambiguity of Rasbora group in Lake Laut Tawar. Approximately 655-bp were amplified from the 5′ region of the mitochondrial cytochrome oxidase subunit I ( cox1 ) gene using the primer pairs (Fish F1 and Fish R1). A total of 14 haplotype sequences were produced from the ingroup where haplotypes 1 to 8 were shared by Eas and Depik, and haplotypes 9 to 14 were belonging to Relo. The genetic divergence varied from 0.2 to 9.6% i.e. between Eas and Relo, 9.6% and between Depik and Relo, 9.5%. The genetic data strongly indicated that Eas and Depik should be regarded as the same species of Rasbora tawarensis .

This research bridges a key phylogeographic gap for Nile tilapia ( Oreochromis niloticus ) in Asia by presenting pioneering DNA barcode data from Indonesia’s Singkil Peat Swamp ecosystem. We obtained partial cytochrome c oxidase subunit I (COI) one sequences from Singkil and complemented them with GenBank data from Bangladesh, China, India, Indonesia, Israel, Malaysia, Philippines, Qatar, Thailand, and Vietnam. Analysis of 67 sequences (639 bp) revealed high genetic diversity (haplotype diversity Hd = 0.933; nucleotide diversity π = 0.03232) with 22 identified haplotypes. Phylogenetic reconstruction identified three well-supported subclades: Subclade I (Indonesia, Vietnam, Malaysia, Philippines, Qatar, Thailand, Israel), Subclade II (Bangladesh, India), and Subclade III (exclusively China). This structure, corroborated by haplotype networks, reflects a complex invasion history driven by human aquaculture transfers rather than natural dispersal. The findings provide crucial genetic evidence for managing O. niloticus as distinct invasive lineages across Asia, with implications for biosecurity and conservation planning in biodiverse regions like Southeast Asia. These results provide crucial baseline data for monitoring spread and implementing targeted management strategies for this economically important yet invasive species.

Haemonchus contortus is a highly pathogenic nematode parasite of sheep and goats. This work was conducted to investigate the population and host variations of the parasitic nematode H. contortus of sheep and goats from Malaysia and Yemen. Eight morphological characters were investigated, namely the total body length, cervical papillae, right spicule, left spicule, right barb, left barb, gubernaculum and cuticular ridge (synlophe) pattern. Statistical analysis showed the presence of morphological variation between populations of H. contortus from Malaysia and Yemen, with minor variation in the synlophe pattern of these isolates. Isolates from each country were grouped together in the scatterplots with no host isolation. Body, cervical papillae and spicule lengths were the most important characters that distinguished between populations of the two countries. This variation between Malaysia and Yemen may be attributed to geographical isolation and the possible presence of a different isolate of this worm in each country.

The groupers are among the fishes that are threatened globally due to their high economic value. However, their biological information is limited, including the white-edged lyretail ( Variola albimarginata ). The fish is considered as the least concern (LC) based on the IUCN category. The objective of the present study was to study some biological aspects of the white-edged lyretail harvested in the northern coast of Aceh. The fishes were collected in several fish landing sites (TPI) and fish market located in Banda Aceh and Aceh Besar District from June to August 2020. A total of 30 fish samples were collected in this study. The total lengths (TL) and weights (W) ranged between 14.30-36.02 cm and 33.2-581.6 g, respectively. In addition, 25 of collected fishes were female with the gonad maturity phases varied from one (1) to four (4) with the gonad-index (GSI) ranged between 0.1758-2.4038. The result of this study will be valuable in developing fisheries management and conservation of the species.

The groupers, locally known as “kerapu” in Indonesia, are commercially valuable fish in Indonesia, including Aceh. The groupers are the first fish family to be plundered in most countries’ fisheries industries. However, the biodiversity information of the groupers fished in Aceh is limited. This study was aimed to inventories the grouper species landed in Aceh fish landing sites. The data collection was performed in some fish landing locations (TPI) located in Aceh. In general, this study revealed that Aceh has high grouper diversity. In total, 35 species of the Epinephelidae family were recorded. Epinephelus was the dominant genus found, followed by Cephalopholis, Plectropomus, Variola, Aethaloperca, Anyperodon , and Hyporthodus . Simeulue, Weh island, and Banda Aceh were the locations with the highest diversity of grouper in Aceh. Overall, the data collected from this study would be beneficial for the future management plan of grouper in Aceh and Indonesia.