Aenigmachanna mahabali Basheer & Ravi 2019, new species

Aenigmachanna mahabali, new species urn:lsid:zoobank.org:act: EFF47D7C-3C6D-4FAD-9066-169E744F425E

Holotype: ICAR-NBFGR / CHAPMAH.1; 127mm SL; India: Kerala: Peringara, near Thiruvalla in Pathanamthitta district. Collected by Arun Vishwanath, 18 April 2018.

Diagnosis. A species of Aenigmachanna as evidenced by the complete absence of a lateral line, an elongate eel-like body, a long-based dorsal fin nearly three-quarters of standard length, and a long-based anal fin, greater than half of standard length, with over 40 rays. Aenigmachanna mahabali can be distinguished from the only other known species in the genus by possessing fewer rays in the dorsal fin (53 vs 56–57), fewer scales in a lateral series (76 vs 83–85), a shorter head (18.5% SL vs 20.7–21.6% SL), a longer upper jaw (64.5% HL vs 60.0–60.8% HL), a smaller eye (9.8% HL vs 12.7–13.3% HL), and in having the pectoral-fin rays extending as filaments well beyond the margin of the fin membrane.

Description: General appearance as in Figures 1–3; morphometric and meristic data are given in Table 1.

The body is slender and elongate, sloping upwards from the snout to the dorsal-fin origin and then very gently sloping downwards to the caudal peduncle. The body is deepest at the origin of the dorsal fin (10.9% SL) and widest at the origin of the anal fin (9.3% SL). The caudal peduncle is deeper (4.6% SL) than long (2.5% SL). The bases of the dorsal and anal fins are long (73.1% and 58.3% SL, respectively), with 53 and 42 rays, respectively. The posterior branch of each of the branched dorsal-fin rays, from the 20th ray posteriorly, is bifurcated distally (Fig. 4). The pectoral fin (14.0% SL) is shorter than the head, and has 12 rays which are produced as filaments beyond the margin of the interradial membrane (Fig. 6). The pelvic fin is absent. The caudal fin is lanceolate, with 14 branched rays. Pored lateral-line scales are absent. There are 76 scales in a lateral series, 12 in a transverse series at the anal-fin origin, and 17 pre-dorsal scales. There are 61 total vertebrae. The bones of the hypural complex are arranged in two groups separated by a distinct gap, with each hypural plate supporting 7 branched rays of the caudal fin (Fig. 5).

The head is moderately long (18.5% SL), widest (51.3% HL) approximately midway, and deepest (53.4% HL) at the nape. The snout (22.7% HL) is broad and blunt. The eyes are small (9.8% HL) and situated dorsolaterally in the anterior third of the head. The mouth is large (64.5% HL), with fleshy lips, and the length of the maxilla is more than twice the distance from the tip of the snout to the posterior margin of the eye. Both upper and lower jaws exhibit multiple rows of minute, pointed teeth. There are 10 prominent caniniform teeth arranged in a single row on the vomer and there is a single row of smaller teeth on the palatines. Cephalic sensory pores are single, without satellite openings, and consists of 2 nasal pores, 7 circumorbital pores, 2 frontal pores, 4 preopercular pores, 2 extrascapular pores, 1 pterotic pore, 1 posttemporal pore, 4 dentary and 1 anguloarticular pores (Fig. 3). There are 10 gill rakers on the lower limb of the first gill arch. There are no scales in the gular region or on the ventral side of the lower jaw. The scales in the postorbital region anterior to the nape are deeply embedded in the skin.

Colouration. In life: The body is uniformly reddish-brown, with the colouration of the ventral surface anterior to the anal-fin origin fading to cream. The scales on the cheek exhibit reflective silvery regions surrounding areas of dark pigment, while those on the operculum are almost entirely silvery. Scales on the body are pigmented basally to about a third of the scale length, with clear distal margins, presenting the appearance of a row of spots along the side. The fins are hyaline, with faint spots on the dorsal-fin membrane and a spot at the base of each dorsal-fin ray.

In preservative: The body is predominantly brown, darker brown dorsally. The ventral side of the head, the chest and belly are cream with spots of darker pigment, especially along the ventral mid-line. The scales exhibit pigmented bases and unpigmented distal regions. The fins are hyaline.

Genetic analysis. The COI sequence generated in this study, representing a barcode for A. mahabali, has been submitted to GenBank under the accession number MK736657. Uncorrected pairwise distances were calculated to be 12.3% between A. mahabali and A. gollum, and ranged from 15.8-24.4% between Aenigmachanna and Channa, and 19.4-21.5% between Aenigmachanna and Parachanna.

Distribution. The species is known from a single location, a well in Peringara, near Thiruvalla in Pathanamthitta district, Kerala, India (Fig. 7). When the fish was found, at the height of summer, the water surface in the well was at a depth of about 5 metres below the ground surface. The specimen came to light when the water in the well, normally clear, suddenly turned muddy and the well was drained to facilitate cleaning. Peringara is situated in a large natural wetland that abuts the Kuttanad lowlands, ‘the rice bowl’ of Kerala.

Etymology. In the mythology of Kerala, Mahabali was a king who conquered the three realms and was banished to the netherworld by Vamana, an avatar of Vishnu. He is, however, allowed to return to the mortal realm once a year, which is celebrated in the festival of Onam. Treated as a noun in apposition.