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Balitorid loaches are a family of fishes that exhibit morphological adaptations to living in fast flowing water, including an enlarged sacral rib that creates a ‘hip’-like skeletal connection between the pelvis and the axial skeleton. The presence of this sacral rib, the robustness of which varies across the family, is hypothesized to facilitate terrestrial locomotion seen in the family. Terrestrial locomotion in balitorids is unlike that of any known fish: the locomotion resembles that of terrestrial tetrapods. Emergence and convergence of terrestrial locomotion from water to land has been studied in fossils; however, studying balitorid walking provides a present-day natural laboratory to examine the convergent evolution of walking movements. We tested the hypothesis that balitorid species with more robust connections between the pelvic and axial skeleton (M3 morphotype) are more effective at walking than species with reduced connectivity (M1 morphotype). We predicted that robust connections would facilitate travel per step and increase mass support during movement. We collected high-speed video of walking in seven balitorid species to analyze kinematic variables. The connection between internal anatomy and locomotion on land are revealed herein with digitized video analysis, μCT scans, and in the context of the phylogenetic history of this family of fishes. Our species sampling covered the extremes of previously identified sacral rib morphotypes, M1 and M3. Although we hypothesized the robustness of the sacral rib to have a strong influence on walking performance, there was not a large reduction in walking ability in the species with the least modified rib (M1). Instead, walking kinematics varied between the two balitorid subfamilies with a generally more ‘walk-like’ behavior in the Balitorinae and more ‘swim-like’ behavior in the Homalopteroidinae. The type of terrestrial locomotion displayed in balitorids is unique among living fishes and aids in our understanding of the extent to which a sacral connection facilitates terrestrial walking.

Khon Kaen Agriculture Journal, 49, 6, 1658-1670

The rheophilic hillstream loaches (Balitoridae) of South and Southeast Asia possess a range of pelvic girdle morphologies, which may be attributed to adaptations for locomotion against rapidly flowing water. Specifically, the connectivity of the pelvic plate (basipterygium) to the vertebral column via a sacral rib, and the relative size and shape of the sacral rib, fall within a spectrum of three discrete morphotypes: long, narrow rib that meets the basipterygium; thicker, slightly curved rib meeting the basipterygium; and robust crested rib interlocking with the basipterygium. Species in this third category with more robust sacral rib connections between the basipterygium and vertebral column are capable of walking out of water with a tetrapod-like lateral-sequence, diagonal-couplet gait. This behavior has not been observed in species lacking direct skeletal connection between the vertebrae and the pelvis. The phylogenetic positions of the morphotypes were visualized by matching the morphological features onto a novel hypothesis of relationships for the family Balitoridae. The morphotypes determined through skeletal morphology were correlated with patterns observed in the pelvic muscle morphology of these fishes. Transitions towards increasingly robust pelvic girdle attachment were coincident with a more anterior origin on the basipterygium and more lateral insertion of the muscles on the fin rays, along with a reduction of the superficial abductors and adductors with more posterior insertions. These modifications are expected to provide a mechanical advantage for generating force against the ground. Inclusion of the enigmatic cave-adapted balitorid Cryptotora thamicola into the most data-rich balitorid phylogeny reveals its closest relatives, providing insight into the origin of the skeletal connection between the axial skeleton and basipterygium.

River-floodplain ecosystems are in delicate balance and are impacted by even minor changes in water availability. In this study, we surveyed fish assemblages and investigated environmental and landscape parameters in a total of 135 floodplain waterbodies (rivers, diversion canals, ponds, irrigation ditches, paddy fields, and wetlands) in the Chao Phraya River Basin in rainy (September 2014) and dry (March 2015) seasons. Factors affecting fish species richness in each type of waterbody were analyzed using generalized linear mixed models. Floodplain area around each surveyed waterbody was a major factor determining fish species richness in rivers, diversion canals, and ponds in the region. The contribution of floodplain area was equivalent to that of hydrology (current velocity, water depth) and water quality (dissolved oxygen, turbidity) in the waterbodies. The population of juvenile fishes was increased in temporarily connected floodplain waterbodies to main rivers compared with isolated waterbodies, and fluvial and lacustrine fishes were observed in the temporary inundated floodplain waterbodies during the rainy season. The high dependence of fish species richness on floodplain area in the region appeared to be a result of the use of inundated floodplains by fish species to forage and breed. Our results highlight the impact of flood control measures that reduces floodplain area. These measures must be reviewed to ensure the conservation of fish biodiversity in the Chao Phraya River Basin, one of the world’s most threatened floodplain systems.

Fishes have adapted a number of different behaviors to move out of the water, but none have been described as being able to walk on land with a tetrapod-like gait. Here we show that the blind cavefish Cryptotora thamicola walks and climbs waterfalls with a salamander-like diagonal-couplets lateral sequence gait and has evolved a robust pelvic girdle that shares morphological features associated with terrestrial vertebrates. In all other fishes, the pelvic bones are suspended in a muscular sling or loosely attached to the pectoral girdle anteriorly. In contrast, the pelvic girdle of Cryptotora is a large, broad puboischiadic plate that is joined to the iliac process of a hypertrophied sacral rib; fusion of these bones in tetrapods creates an acetabulum. The vertebral column in the sacral area has large anterior and posterior zygapophyses, transverse processes and broad neural spines, all of which are associated with terrestrial organisms. The diagonal-couplet lateral sequence gait was accomplished by rotation of the pectoral and pelvic girdles creating a standing wave of the axial body. These findings are significant because they represent the first example of behavioural and morphological adaptation in an extant fish that converges on the tetrapodal walking behaviour and morphology.

The relationships between environmental variables as descriptors to the fish community, in terms of species diversity indices, and the fish assemblage patterns along the longitudinal gradient in a rhitral environment of a large river system located in the Indo-Burma hot spot (Ping-Wang River Basin) were studied. Fish data and water quality parameters were collected between January 1996 and April 2009. The three most diverse families were Cyprinidae, Balitoridae, and Cobitidae, respectively. Three physicochemical parameters (i.e., DO, water temperature, and pH) and three geo-morphological parameters (i.e., altitude, distance from the sea, and discharge) showed statistically significant to diversity parameters (P value

Thailand is among the countries that ranked top in freshwater fish diversity, of which 843 freshwater fish species, including 13 elasmobranch fishes, have been officially recorded. Presently, the integrity of freshwater fish community is threatened by many stressors from human activities, in particular the river damming. In this paper, we illustrate the impacts to freshwater fish diversity by various dam types in Thailand. The major serious impact of river damming is the blockage of fish migratory routes, both for the species that migrate within river system and migrate between the river and the sea. So far, there is no any fish passage that reveals the effective performance because it is difficult to deal with the many fish species, with various modes of swimming and water flow preferences, in a single designed fish passage. The consequent results are the extirpation of the migratory species and, then, changes in fish community structures. The mitigation measure of opening the sluice gates for a certain period is recommended. This measure is beneficial for the fish migrations both for the dams in the middle portion and lower portion, i.e., brackish area, of the river, which allows the fish to complete their life cycles and can manipulate the fish assemblage patterns.

Schistura sirindhornae, a new species of nemacheilid, is described from the Nan River basin in northern Thailand. It is distinguished from all other species of Schistura in having overlapping scales on the entire body similar to scales of balitorids, transparent scales on the belly and thorax, a lateral-line canal that is similar to that of most cyprinids and balitorids in being present across the entire lateral-line surface of the scale instead of being represented only by a pore. It also has a unique color pattern of irregular brown bars on the back and side of the faint yellow-orange body, a bright triangular orange mark on the occiput, an orange crown-shaped mark between the eyes, an uninterrupted black mark along the base of the dorsal fin, a crescent-shaped bar on the base of the caudal fin, and bright iridescent orange areas on the upper and lower extremities of the caudal-fin base. Schistura sirindhornae is known only from the upper Nan River drainage, Nan Province, Thailand.

Physoschistura chulabhornae, new species, is described from Maechaem River, a tributary of Ping River, upper Chaophraya River drainage, Chiangmai province, Thailand. It is distinguished from all other known species of Physoschistura in having an incomplete lateral line reaching at least to the origin of the anal fin with 62-83 lateral-line canal pores, the dorsal-fin origin slightly in front of the pelvic-fin origin, no axillary pelvic lobe, and a suborbital flap in the shape of a hammer head in the male.

Schistura maejotigrina, new species, is described from Maechaem River, a tributary of Ping River, in the upper Chao Phra-ya River drainage, Chiang Mai Province, Thailand. It is distinguished from all other species of Schistura in having 21–24dark tiger-stripe black bars on the side of the body and 6½–7½ branched dorsal soft rays. The species is medium-sized,reaching 53.0 mm SL (69.6 mm TL), and is known only from the Maechaem River system, Ping River drainage, northernChao Phraya River basin, Chiang Mai Province, Thailand. It lives in fast running, clear water over a substrate of mixed gravel, small stone and sand.