Conservation is imperative for the Asian snakeheads Channa striata, as the species has been overfished due to its high market demand. Using maternal markers (mitochondrial cytochrome c oxidase subunit 1 gene (COI)), we discovered that evolutionary forces that drove population divergence did not show any match between the genetic and morphological divergence pattern. However, there is evidence of incomplete divergence patterns between the Borneo population and the populations from Peninsular Malaysia. This supports the claim of historical coalescence of C. striata during Pleistocene glaciations. Ecological heterogeneity caused high phenotypic variance and was not correlated with genetic variance among the populations. Spatial conservation assessments are required to manage different stock units. Results on DNA barcoding show no evidence of cryptic species in C. striata in Malaysia. The newly obtained sequences add to the database of freshwater fish DNA barcodes and in future will provide information relevant to identification of species.

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Mesohabitat selection in fluvial fishes was studied in a small tropical stream of the Malay Peninsula. A total of 681 individuals representing 24 species were sampled at 45 stations within heterogeneous stream (ca. 1 km in length), in which water depth, water velocity, substrate size, and riparian canopy cover were measured as environmental variables. A canonical correspondence analysis (CCA) yielded a diagram that shows a specific mesohabitat selection of the fish assemblage, in which the species were plotted widely on the CCA1-CCA2 biplot. Generalized linear model also revealed a significant pattern of the mesohabitat selection of several species. Water velocity and substrate size mainly separated on CCA1, indicating variation of pool (deep, slow-flow section) and riffle (shallow, fast-flow section) structures is a primary factor of mesohabitat selection in the fluvial fish assemblage. The mean body weight of species significantly correlated with CCA1; larger species tended to inhabit pools, while small ones occupied riffles. The riparian canopy cover separated on CCA2. The trophic level of species significantly correlated with CCA2; herbivorous species (low trophic level) selected open sites without riparian cover, whereas omnivorous/carnivorous (middle-high trophic level) species preferred highly covered sites. In conclusion, our results suggest that mesohabitat selection is closely related to the species feeding habit, which is consistent with the results of previous studies.

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