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Tropical animals are characterized by showy ornaments and conspicuous body colours as compared with their temperate relatives. Some recent studies have hypothesized that sexual selection pressures are stronger in the tropics than in the temperate zone. Although negative correlations between latitude and the degree of sexual dimorphism would support this hypothesis, phylogeny should be taken into account in such comparative studies. Comparisons of the degree of sexual dimorphism in body size and fin lengths among species of the Adrianichthyidae, a freshwater fish family having a wide geographical range throughout Southeast and East Asia, revealed that lower latitude species are sexually more dimorphic in all characters than higher latitude species. Phylogenetic generalized least squares analyses using a mitochondrial DNA phylogeny demonstrated that the negative correlations between latitude and the degree of sexual dimorphism become non-significant when phylogeny is considered, but that the variance in the degree of sexual dimorphism is explained not only by phylogeny but also almost equally by latitude. Ancestral state reconstruction indicated that sexual dimorphisms have evolved independently even within major clades. These findings are consistent with the view that tropical species are exposed to stronger sexual selection pressures than temperate species. We discuss possible causes of the latitudinal variation in sexual selection pressure.

The food habits of three non-native cichlid fishes, Mayan cichlid (Mayaheros urophthalmus), Mozambique tilapia (Oreochromis mossambicus) and Nile tilapia (O. niloticus), in the lowermost Chao Phraya River basin, Thailand, was examined by stomach contents analysis. The index of preponderance, an index of the importance of prey items, was calculated from two relative metrics of prey quantity: percent frequency and percent volume. The index of niche breadth and the overlap coefficient were calculated to compare the breadth of food habits among the size classes and species groups. The M. urophthalmus mainly preyed on fish scales, detritus and aquatic invertebrates (molluscs and crustaceans). The O. mossambicus and O. niloticus fed mostly on detritus. The diets of the latter two species overlapped almost completely; however, green filamentous algae mixed with detritus was observed in the diet of the O. niloticus only. The observation that fish scales were a predominant food source in the stomach of M. urophthalmus (high importance value 45.48%) was specific to this study area.

The Indian subcontinent has an origin geologically different from Eurasia, but many terrestrial animal and plant species on it have congeneric or sister species in other parts of Asia, especially in the Southeast. This faunal and floral similarity between India and Southeast Asia is explained by either of the two biogeographic scenarios, ‘into-India’ or ‘out-of-India’. Phylogenies based on complete mitochondrial genomes and five nuclear genes were undertaken for ricefishes (Adrianichthyidae) to examine which of these two biogeographic scenarios fits better. We found that Oryzias setnai , the only adrianichthyid distributed in and endemic to the Western Ghats, a mountain range running parallel to the western coast of the Indian subcontinent, is sister to all other adrianichthyids from eastern India and Southeast–East Asia. Divergence time estimates and ancestral area reconstructions reveal that this western Indian species diverged in the late Mesozoic during the northward drift of the Indian subcontinent. These findings indicate that adrianichthyids dispersed eastward ‘out-of-India’ after the collision of the Indian subcontinent with Eurasia, and subsequently diversified in Southeast–East Asia. A review of geographic distributions of ‘out-of-India’ taxa reveals that they may have largely fuelled or modified the biodiversity of Eurasia.

The air sac catfish, Heteropneustes fossilis (Siluriformes: Heteropneustidae), is widely distributed in freshwaters of the Indian subcontinent and mainland southeast Asia. No comprehensive molecular studies that cover the broad distributional areas have been carried out to date. Here, we conducted molecular phylogenetic analyses using both mitochondrial and nuclear gene sequences to suggest that the Heteropneustes fossilis species complex consists of three clades that may potentially be separate species with distinct geographical distribution (southeast Asia, northeastern India, and southwestern India). The first and second clades are more closely related to each other than they are to the third clade. Within the first clade there is a basal divergence of a subclade consisting of individuals from the Upper Irrawaddy River basin of Myanmar, which share some morphological traits with members of the Indian clades. Our molecular and morphological data are congruent with hypotheses that the Early-Middle Miocene disconnection between the paleo-Tsangpo River and the Irrawaddy River caused the vicariant divergence between southeast Asian and northeastern Indian clades, and that the southeast Asian Heteropneustes originated from the Upper Irrawaddy.

We report on the occurrence and possible establishment of a non-native cichlid fish in a brackish-water system in the lower Chao Phraya River delta region, Thailand. Although, the possibility of some degree of introgressive hybridization can not be ruled out, Thailand specimens agree best with Mayan Cichlid “Cichlasoma” urophthalmus (Gunther 1862). Our collections represent the first records of this New World, highly-invasive, euryhaline fish from Thailand and coincides with recent collections from Singapore. Positive identification of specimens as “C.” urophthalmus requires caution due to the diversity of the Cichlidae (>1,300 species), widespread introduction of many family members, variation within species, extensive interspecific overlap in characters, and proliferation of artificial cichlid hybrids (e.g., Flowerhorns). We first became aware of the Thailand population in 2005 when “C.” urophthalmus began appearing in the catches of local fishermen. We visited the site in November 2006 and obtained and examined voucher specimens. The abundance and wide size range of juveniles and adults in local ponds and an adjacent canal is evidence of natural reproduction. Because water bodies throughout the Chao Phraya delta are interconnected and subject to flooding, it is likely that “C.” urophthalmus is already established and is dispersing, but surveys and monitoring are needed to determine their exact geographic range. The Thailand population is compared to “C.” urophthalmus introduced into Florida (USA). Based on what is known about Florida “C.” urophthalmus, it is predicted that this cichlid will further invade coastal and inland waters in Thailand and elsewhere in Southeast Asia. This cichlid has a long history in the aquarium trade in Europe. However, there are no records from the wild in European waters and, because of the colder climate, the possibility of establishment in that region is relatively low.

Mitochondrial DNA sequences of approximately 1.5 kbp including the NADH dehydrogenase subunit 2 (ND2) gene and its flanking gene regions were determined for 20 species from the freshwater fish family Channidae and 3 species from Nandidae, Badidae, and Osphronemidae. Channa orientalis and C. gachua had an approximately 170-bp insertion between the tRNAMet and ND2 genes, where a 5′-half of the insertion was similar to the 5′-end portion of the ND2 gene and a 3′-half was homologous to the tRNAMet gene. This insertion may thus have originated from a tandem gene duplication that occurred in a common ancestor of these two sister species. Molecular phylogenetic analyses from different tree-building methods consistently suggested the mutual monophyly of the African and Asian taxa and the existence of several clades within the Asian taxa, some of which correspond to distinct morphological features. Our molecular phylogeny clearly supported multiple independent losses of pelvic fins on Asian lineages in parallel. Divergence time estimation based on some reasonable assumptions without assuming the molecular clock suggested the early Cretaceous divergence of the African and Asian channids. The results thus support an ancient vicariant divergence of the African and Asian channids, rather than the more recent dispersal between African and Eurasian continents.

A new species of channid fish, genus Channa, is described from 7 specimens collected from the vicinity of Hepu, Guangxi Province, southern China. The new species, Channa nox, is distinguished from all other channid species by the following combination of characters: absence of pelvic fins, small rounded head (22.1%–26.8% SL), narrow interorbital width (19.6%–26.7% HL), short snout length (3.6%–5.1% SL), predorsal and prepectoral lengths (26.9%–28.4% SL and 24.8%–28.3% SL, respectively), 47–51 dorsal fin rays, 31–33 anal fin rays, 55–63 lateral line scales, 5.5–6.5 scales above lateral line, 9–13 cheek scales, 53–55 total vertebrae, 1 or 2 scale(s) on each side of lower jaw undersurface, the black upper half of body with 8–11 irregular (often anteriorly pointed V-shaped) bands or blotches, a large white-rimmed black ocellus on caudal peduncle and sparse white spots on the dark brown body and dorsal and caudal fins, as well as the shape of the hyomandibular process of the suprabranchial organs. Channa nox is sympatrically distributed with its morphologically most similar congener, C. asiatica.

A new cyprinid fish, Garra waensis, is described from the Wa River, a tributary of the Nan River of the Chao Phraya River system in northern Thailand. The species is distinguishable from its congeners by the combination of the following characters: the absence of barbels; 7 branched dorsal fin rays; 31-37 lateral-line scales; 10-12 circumpeduncular scales; a small and broad head (head length [HL] 22.7-26.1% in standard length, head depth 56.1-64.9% HL, head width 74.0-85.0 % HL); a weakly developed proboscis in front of nostrils; the presence of reddish-orange spots (white or dull yellowish white in preserved specimens) on the side of the body; and a dark mid-lateral stripe running from the upper edge of the gill opening to the caudal peduncle and expanding into a large anteriorly-pointed triangular blotch at the end of the body (in preserved condition). A vomero-palatine organ of the species is also described in detail for the first time for Asian species of Garra. The genus Placocheilus is treated as a junior synonym of Garra.

The holotype of Channa siamensis (Gunther, 1861) was examined and compared with specimens of all other channid species currently considered to be valid (2 genera, 27 species). As all of the examined morphological characters (meristics, morphometrics, coloration, a patch of gular scales, and cephalic sensory pores) of the small-sized hototype (74.2 mm SL) agree with those for C. lucius except for slight gaps in predorsal length and interorbital width (subject to allometric changes), the authors concluded that C. siamensis is a junior synonym of C. lucius (Cuvier in Cuvier and Valenciennes, 1831).

Channa panaw sp. nov. (Channidae) is described from 32 specimens collected from the Irrawaddy and Sittang River basins, Myanmar. It is distinguishable from all known congeners by the combination of the following characters: 32–35 dorsal fin rays, 23–24 anal fin rays, 17–20 pectoral fin rays, 39–41 lateral line scales, 39–41 total vertebrae, one large scale on each side of the lower jaw (rarely 2 on one side), pelvic fin length always more than 50% of pectoral fin length, and 7–12 irregular black blotches on the upper half of the body.

The nominal species, Thysanichthys evides Jordan and Thompson, 1914 (Scorpaenidae), originally described from Misaki, Japan, has not been reported since its original description. Examination of the type specimens of T. evides showed them to be identical with the holotype and non-type specimens of a species previously widely-regarded as Scorpaenodes littoralis (Tanaka, 1917), originally described as Sebastella littoralis, also from Misaki. Thysanichthys evides is herein regarded as a senior synonym of Sebastella littoralis, and is a valid species of Scorpaenodes.

A new cyprinid fish, Garra waensis, is described from the Wa River, a tributary of the Nan River of the Chao Phraya River system in northern Thailand. The species is distinguishable from its congeners by the combination of the following characters: the absence of barbels; 7 branched dorsal fin rays; 31–37 lateral-line scales; 10–12 circumpeduncular scales; a small and broad head (head length [HL] 22.7–26.1% in standard length, head depth 56.1–64.9% HL, head width 74.0–85.0 % HL); a weakly developed proboscis in front of nostrils; the presence of reddish-orange spots (white or dull yellowish white in preserved specimens) on the side of the body; and a dark mid-lateral stripe running from the upper edge of the gill opening to the caudal peduncle and expanding into a large anteriorly-pointed triangular blotch at the end of the body (in preserved condition). A vomero-palatine organ of the species is also described in detail for the first time for Asian species of Garra. The genus Placocheilus is treated as a junior synonym of Garra.