Schistura sonarengaensis, a new species of cave-dwelling loach (Teleostei: Nemacheilidae) from Meghalaya, northeast India.

A new species of nemacheilid loach, Schistura sonarengaensis sp. nov., is described from three cave-dwelling populations (Barak-Surma-Meghna drainage) in the South Garo Hills district of Meghalaya, India. The new species possesses prominent eyes but is easily distinguished from all the congeners of the genus Schistura from Barak-Surma-Meghna and adjacent rivers drainages of northeast Indian (except S. syngkai) in having 13-26 vertically elongated to circular mid-lateral black blotches (brownish in life) overlayered on a grayish-black mid-lateral stripe on a dull white or pale-beige (golden brown in life) body. However, it can be easily distinguished from S. syngkai in having a complete (vs. incomplete) lateral line with more 72-89 (vs. 19-42) lateral-line pored scales, greater pre-dorsal length (48.5-53.1 vs. 41.9-44.1 %SL), a wider body at dorsal-fin origin (11.3-16.7 vs. 9.4-10.3 %SL), greater dorsal (18.1-21.1 vs. 15.1-17.0 %SL) and lateral (20.9-24.1 vs. 17.4-18.9 %SL) head length, a wider head (14.5-18.5 vs. 11.6-13.3 %SL), and moderately forked (vs. emarginated) caudal fin. Further, molecular analysis confirms the distinctiveness of S. sonarengaensis sp. nov. from its congeners found in northeast India by significant divergences with uncorrected genetic distance ranging from 3.7% to 17.3% in the mitochondrial cytochrome c oxidase subunit I (COI) gene dataset. The phylogenetic position of the new species with its sister species was evaluated using maximum likelihood and Bayesian analysis. The species delimitation approaches assemble species by automatic partitioning (ASAP) and Poisson tree processes (PTP) utilized for testing species assignments consistently identified our test group as a distinct species from its sister species. Although the new species lacks typical morphological adaptations usually associated with a subterranean life, such as complete absence (or vestigial presence) of eyes and pigmentation, it exhibits a reduction of pigmentation when compared to the epigean congeners.

Identification and characterisation of emerging fish pathogens Aeromonas veronii and Aeromonas hydrophila isolated from naturally infected Channa punctata.

Naturally infected Channa punctata exhibiting bacterial septicemic syndrome including ulcerations along with mortality records were collected from a fish farm in Assam during winter season (early November 2020 to early January 2021). The moribund fishes were subjected for bacterial isolation followed by identification of the bacteria. Two dominant emerging bacterial pathogens were identified as Aeromonas veronii (isolate ZooGURD-01) and Aeromonas hydrophila (isolate ZooGURD-05) by standard biochemical characterization and 16S rRNA and rpo B gene amplification. Re-infection experiments of both the bacterial isolates in healthy disease-free C. punctata showed similar symptoms to that of natural infection thus confirming their virulence. The LD50 calculated during challenge test for both the isolates ZooGURD-01 and ZooGURD-05 found to be pathogenic at 2.6 × 104 and 1.6 × 104 CFU/fish respectively. Further PCR amplification of specific virulent genes (aerolysin, hemolysin and enterotoxin) confirmed pathogenicity for both isolates. Histopathological examinations of liver and kidney in re-infection experiments showed prominent changes supporting bacterial septicaemia. Antibiotic sensitivity pattern showed that the isolates ZooGURD-01 and ZooGURD-05 were sensitive to 22 and 19 out of 25 antimicrobials respectively. The present study was the first report on the mortality of farmed C. punctata associated with natural infection caused by A. veronii and A. hydrophila with no record of pathogenicity of A. veronii in C. punctata.

Description of a new species of Mustura Kottelat (Teleostei: Nemacheilidae) from the Brahmaputra drainage, India.

Mustura subhashi, new species, is described from the Dikal River, a north bank tributary of the Brahmaputra drainage in Arunachal Pradesh. It is distinguished from all its congeners by having a colour pattern of 14-23 dark-greyish black to dark brown irregular bars on a greyish to pale beige body; pre-dorsal bars thin, numerous, wider than interspaces, weakly contrasted, uniting dorsally at lateral one-third or midway on flank to form thicker bars, coalescing further at lateral one-fifth and continuous on dorsum with contralateral bars; bars below dorsal fin exhibiting similar condition but slightly wider than pre-dorsal bars; post-dorsal bars thicker than anterior bars, wider than interspaces, sharply contrasted, rarely coalescing on flank; and a short bar along the caudal mid-line, rarely forming a blotch. Based on re-examination of the type specimens and additional materials, Mustura dikrongensis is confirmed as a species belonging to Mustura, and M. harkishorei is not sufficiently diagnosed from 'Nemacheilus' corica.

Isolation and characterization of two virulent Aeromonads associated with haemorrhagic septicaemia and tail-rot disease in farmed climbing perch Anabas testudineus.

Diseased Anabas testudineus exhibiting signs of tail-rot and ulcerations on body were collected from a fish farm in Assam, India during the winter season (November 2018 to January 2019). Swabs from the infected body parts were streaked on sterilized nutrient agar. Two dominant bacterial colonies were obtained, which were then isolated and labelled as AM-31 and AM-05. Standard biochemical characterisation and 16S rRNA and rpoB gene sequencing identified AM-31 isolate as Aeromonas hydrophila and AM-05 as Aeromonas jandaei. Symptoms similar to that of natural infection were observed on re-infecting both bacteria to disease-free A. testudineus, which confirmed their virulence. LC50 was determined at 1.3 × 104 (A. hydrophila) and 2.5 × 104 (A. jandaei) CFU per fish in intraperitoneal injection. Further, PCR amplification of specific genes responsible for virulence (aerolysin and enterotoxin) confirmed pathogenicity of both bacteria. Histopathology of kidney and liver in the experimentally-infected fishes revealed haemorrhage, tubular degeneration and vacuolation. Antibiotic profiles were also assessed for both bacteria. To the best of our knowledge, the present work is a first report on the mortality of farmed climbing perch naturally-infected by A. hydrophila as well as A. jandaei, with no records of pathogenicity of the latter in this fish.

Psilorhynchus nahlongthai, a new fish species (Teleostei: Psilorhynchidae) from the Brahmaputra drainage, northeast India.

Psilorhynchus nahlongthai, a new psilorhynchid fish, is described from the Diyung River, a tributary to the Kopili River (itself a southern tributary of the Brahmaputra drainage) in Assam, northeast India. It is placed in the Psilorhynchus balitora species group and can be easily distinguished from all other members of this group by a combination of the following characters: dense and prominent tuberculation on the head region; thick and long pre- and post-epiphyseal fontanelles on the neurocranium; 9 + 8 caudal-fin rays; and 34 (24 + 10) vertebrae. Genetic divergence between P. nahlongthai and members of the P. balitora species group from the Brahmaputra and neighbouring drainages, with K2P distances ranging 3.7%-14.7% and 7.4%-20.7% in the mitochondrial COI and cyt b gene datasets respectively, support its report as a new species.

A new species of stone loach (Teleostei: Nemacheilidae: Schistura) from Arunachal Pradesh, India.

Schistura rebuw, new species, is described from the Kameng River, a north-bank tributary of the Brahmaputra, Arunachal Pradesh, India. The new species is easily distinguished from all known congeners in the Brahmaputra basin by its unique sexual dimorphism, specifically a suborbital slit in adult females, and a suborbital flap in adult males; and a colour pattern of 10-11 blackish bars on a greyish-beige body, the pre-dorsal bars mostly broken or incomplete, coalescing dorsally in a more or less alternate fashion.

Schistura syngkai, a new fish species (Teleostei: Nemacheilidae) from Meghalaya, northeast India.

Schistura syngkai, a new stone loach, is described from the Twahdidoh Stream of Wahblei River (Surma-Meghna drainage) in Meghalaya, northeast India. It is unique among its Indian congeners in having a prominent dark-brown to blackish mid-lateral stripe about an eye diameter or more in width, overlain on 12-18 vertically-elongate black blotches on a golden-brown to amber body. Additionally, the species possesses an incomplete lateral line and a slightly emarginate caudal fin, and exhibits no apparent sexual dimorphism.

Schistura larketensis, a new cavernicolous fish (Teleostei: Nemacheilidae) from Meghalaya, Northeast India.

Schistura larketensis, a new species of cavernicolous loach, is described from Khung, a limestone cave in Meghalaya, India. The species differs from Schistura papulifera, its only troglomorphic congener from northeast India, in having a smooth ventral surface of the head, the presence of a small cylindrical axillary pelvic lobe, and the presence of three pores in the supratemporal canal of the cephalic lateral-line system. Apart from these differences, the species can be immediately distinguished from all other species of Schistura from the Brahmaputra River and neighboring basins by the complete absence (or only vestigial presence) of eyes.