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.