Natal origin and migration pathways of Mekong catfish (Pangasius krempfi) using strontium isotopes and trace element concentrations in environmental water and otoliths.

To improve our knowledge of the migration pathway of a highly threatened fish species along the Mekong River, strontium isotope ratios (87Sr/86Sr) and 18 trace element concentrations were measured in the water and in the otoliths of an anadromous catfish, Pangasius krempfi, to infer its natal origin and potential migration pathways. Water was sampled at 18 locations along the mainstream, tributaries and distributaries of the Mekong River. To check for accuracy and precision, measurements of the 87Sr/86Sr ratios and trace element concentrations were then compared in two laboratories that use different analytical methods. Differences in trace element concentrations between locations were not significant and could not, therefore, be used to discriminate between migration pathways. However, the Mekong mainstream, tributaries and distributaries could all be discriminated using Sr isotopes. The 87Sr/86Sr profiles recorded in P. krempfi otoliths showed that there were three contingents with obligate freshwater hatching and variable spawning sites along the Mekong mainstream, from Phnom Penh (Cambodia) to Nong Khai (Thailand) or further. After hatching, the fish migrated more or less rapidly to the Mekong Delta and then settled for most of their lifetime in brackish water. Spawning habitats and migration routes may be threatened by habitat shifts and the increasing number of hydropower dams along the river, especially the contingents born above Khone Falls (Laos). The conservation of P. krempfi, as well as other migratory fish in the Mekong River, requires agreements, common actions and management by all countries along the Mekong River. This study highlighted the importance of using both Sr/Ca and 87Sr/86Sr ratios to understand life history of anadromous fishes as the 87Sr/86Sr ratio in the water was shown to be less effective than the Sr/Ca ratio in identifying movements between different saline areas.

Condition Index, Reproduction and Feeding of Three Non-Obligatory Riverine Mekong Cyprinids in Different Environments.

Condition index, reproduction and feeding of three non-obligatory riverine Mekong cyprinids namely Hampala dispar, Hampala macrolepidota and Osteochilus vittatus were examined. The samples were from the Nam Ngiep (NN) River and Bueng Khong Long (BKL) Swamp, which are the representative of the lotic- and lentic-environments, respectively. These two habitats lay in the same geographical area but on the opposite banks of the Mekong mainstream. The samplings were conducted between May 2017 and April 2018. There were 365 H. dispar, 259 H. macrolepidota and 298 O. vittatus samples in this study. The condition index of all three species were beyond 90% implying they can live well in both lotic and lentic environments. Reproductions of all three species were taken place in both environments with two peaks at the onset and end of rainy season. The samples from BKL showed early maturation than NN samples in all three (3) species. Feeding plasticity, though dominant by insects, was observed in Hampala spp., while O. vittatus can utilise any available detritus in both environments. Results clearly show that all the three selected non-obligatory riverine fish species can live very well in either lotic or lentic environments and imply that they can adjust themselves to reservoir environment.

Taxonomic revision of the genus Poropuntius (Teleostei: Cyprinidae) in Peninsular Malaysia.

Up to three nominal species of the cyprinid fish genus Poropuntius (i.e. P. deauratus [Valenciennes in Cuvier Valenciennes 1842], P. normani [Smith 1931], and P. smedleyi [de Beaufort 1933]) have been reported to occur in Peninsular Malaysian freshwater ecosystems. However, low morphological differentiation among species of Poropuntius causes confusion and it is still unknown how many valid species of Poropuntius occur in this region. The goal of this study is to review the taxonomic status of Poropuntius in Peninsular Malaysia by using morphological and molecular characters. Principal Component Analysis (PCA) on a morphometric dataset including 281 specimens of Poropuntius from Peninsular Malaysia and P. normani from Thailand (type locality) failed to identify non-overlapping clusters within sampled specimens. A phylogenetic tree based on cytochrome oxidase subunit I (COI) showed intraspecific levels of genetic differentiation within Poropuntius of Peninsular Malaysia and the specimens of P. normani from Thailand form a monophyletic group. Our results strongly support the presence of only one species of Poropuntius in Peninsular Malaysia, P. normani. We demonstrate that P. smedleyi described from Johor, southern Peninsular Malaysia, is a junior synonym of P. normani. The previous reports of the presence of P. deauratus in Peninsular Malaysia are doubtful because this species was described from Vietnam where, in all evidence, it is endemic.

Phylogenetic analysis of trophic niche evolution reveals a latitudinal herbivory gradient in Clupeoidei (herrings, anchovies, and allies).

Biotic and abiotic forces govern the evolution of trophic niches, which profoundly impact ecological and evolutionary processes and aspects of species biology. Herbivory is a particularly interesting trophic niche because there are theorized trade-offs associated with diets comprised of low quality food that might prevent the evolution of herbivory in certain environments. Herbivory has also been identified as a potential evolutionary "dead-end" that hinders subsequent trophic diversification. For this study we investigated trophic niche evolution in Clupeoidei (anchovies, sardines, herrings, and their relatives) and tested the hypotheses that herbivory is negatively correlated with salinity and latitude using a novel, time-calibrated molecular phylogeny, trophic guilds delimited using diet data and cluster analysis, and standard and phylogenetically-informed statistical methods. We identified eight clupeoid trophic guilds: molluscivore, terrestrial invertivore, phytoplanktivore, macroalgivore, detritivore, piscivore, crustacivore, and zooplanktivore. Standard statistical methods found a significant negative correlation between latitude and the proportion of herbivorous clupeoids (herbivorous clupeoid species/total clupeoid species), but no significant difference in the proportion of herbivorous clupeoids between freshwater and marine environments. Phylogenetic least squares regression did not identify significant negative correlations between latitude and herbivory or salinity and herbivory. In clupeoids there were five evolutionary transitions from non-herbivore to herbivore guilds and no transitions from herbivore to non-herbivore guilds. There were no transitions to zooplanktivore, the most common guild, but it gave rise to all trophic guilds, except algivore, at least once. Transitions to herbivory comprised a significantly greater proportion of diet transitions in tropical and subtropical (<35°) relative to temperate areas (>35°). Our findings suggest cold temperatures may constrain the evolution of herbivory and that herbivory might act as an evolutionary "dead-end" that hinders subsequent trophic diversification, while zooplanktivory acts as an evolutionary "cradle" that facilitates trophic diversification.

Revision of the horseface loaches (Cobitidae, Acantopsis), with descriptions of three new species from Southeast Asia.

Acantopsis (Cobitidae) is revised based on analysis of morphological and molecular data. Four of the six available names, A. dialuzona, A. spectabilis, A. octoactinotos, and A. thiemmedhi, are valid, and three new species, A. rungthipae, A. dinema, and A. ioa, are described. All species are described morphologically, distributions are mapped, and relationships are discussed for those for which molecular data (CO1, RAG1) are available. Labial barbels, color pattern, and meristic counts are the most diagnostic features. Although the long snout of Acantopsis is perhaps the most emblematic attribute of the genus, its relative length increases with growth, reducing its taxonomic value. Species can be difficult to identify on the basis of color pattern alone, as habitat and preservation methods appear to strongly influence the color pattern. Despite interspecific overlap of some highly variable traits, each species has a unique set of morphological characteristics that remain observable even when the color pattern is obscured, and some species are restricted to single drainages, greatly simplifying identification. The phylogenetic analyses revealed high molecular divergence between even the most morphologically similar species, with mean uncorrected CO1 p-distances between species ranging from 12.1-15.4%. Species of Acantopsis exhibit significant genetic structuring consistent with recognized freshwater ecoregions. Acanthopsis lachnostoma Rutter 1897, from Swatow, China, is not assignable to Acantopsis.

Impacts of Dams and Global Warming on Fish Biodiversity in the Indo-Burma Hotspot.

Both hydropower dams and global warming pose threats to freshwater fish diversity. While the extent of global warming may be reduced by a shift towards energy generation by large dams in order to reduce fossil-fuel use, such dams profoundly modify riverine habitats. Furthermore, the threats posed by dams and global warming will interact: for example, dams constrain range adjustments by fishes that might compensate for warming temperatures. Evaluation of their combined or synergistic effects is thus essential for adequate assessment of the consequences of planned water-resource developments. We made projections of the responses of 363 fish species within the Indo-Burma global biodiversity hotspot to the separate and joint impacts of dams and global warming. The hotspot encompasses the Lower Mekong Basin, which is the world's largest freshwater capture fishery. Projections for 81 dam-building scenarios revealed progressive impacts upon projected species richness, habitable area, and the proportion of threatened species as generating capacity increased. Projections from 126 global-warming scenarios included a rise in species richness, a reduction in habitable area, and an increase in the proportion of threatened species; however, there was substantial variation in the extent of these changes among warming projections. Projections from scenarios that combined the effects of dams and global warming were derived either by simply adding the two threats, or by combining them in a synergistic manner that took account of the likelihood that habitat shifts under global warming would be constrained by river fragmentation. Impacts on fish diversity under the synergistic projections were 10-20% higher than those attributable to additive scenarios, and were exacerbated as generating capacity increased-particularly if CO2 emissions remained high. The impacts of dams, especially those on river mainstreams, are likely to be greater, more predictable and more immediately pressing for fishes than the consequences of global warming. Limits upon dam construction should therefore be a priority action for conserving fish biodiversity in the Indo-Burma hotspot. This would minimize synergistic impacts attributable to dams plus global warming, and help ensure the continued provision of ecosystem services represented by the Lower Mekong fishery.

Potential effects of hydroelectric dam development in the Mekong River basin on the migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus) elucidated by otolith microchemistry.

The migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus), two of the most economically important fish species in the Mekong River, was studied using an otolith microchemistry technique. Fish and river water samples were collected in seven regions throughout the whole basin in Thailand, Laos and Cambodia over a 4 year study period. There was coherence between the elements in the ambient water and on the surface of the otoliths, with strontium (Sr) and barium (Ba) showing the strongest correlation. The partition coefficients were 0.409-0.496 for Sr and 0.055 for Ba. Otolith Sr-Ba profiles indicated extensive synchronized migrations with similar natal origins among individuals within the same region. H. siamensis movement has been severely suppressed in a tributary system where a series of irrigation dams has blocked their migration. H. lobatus collected both below and above the Khone Falls in the mainstream Mekong exhibited statistically different otolith surface elemental signatures but similar core elemental signatures. This result suggests a population originating from a single natal origin but bypassing the waterfalls through a passable side channel where a major hydroelectric dam is planned. The potential effects of damming in the Mekong River are discussed.