Aplocheilus andamanicus ( Köhler, 1906 )

Katwate, Unmesh, Kumkar, Pradeep, Britz, Ralf, Raghavan, Rajeev & Dahanukar, Neelesh, 2018, The identity of Aplocheilus andamanicus (Köhler, 1906) (Teleostei: Cyprinodontiformes), an endemic Killifish from the Andaman Islands, with notes on Odontopsis armata van Hasselt, Zootaxa 4382 (1), pp. 159-174 : 161-170

Aplocheilus andamanicus ( Köhler, 1906)

( Fig. 1A–C , 2A–B , 3A–B )

Haplochilus panchax (non Hamilton, 1822): Day (1878: 523)

Haplochilus andamanicus Köhler, 1906: 388

Panchax panchax (non Hamilton, 1822): Annandale & Hora (1925)

Aplocheilus panchax (non Hamilton, 1822): Herre (1939, 1941); Rao et al. (2000); Lazara (2001); Palavai & Davidar (2009)

Material examined. Aplocheilus andamanicus: Day material (syntypes) from the Andamans: BMNH 1870.5.18.34-36, 3 ex., 61.7–74.8 mm SL, Port Blair, coll. F. Day ; BMNH 1889.2.1.2107-2110, 4 ex., 50.2–56.3 mm SL, Andamans , coll. F. Day. Additional topotypic material : BNHS FWF 562 to 568, 7 ex., 27.8–65.2 mm SL, Sholbay 14, South Andaman , Andaman and Nicobar Union Territory, India (11°51'44.48"N, 92°44'29.06"E, 47m asl.), coll. U. Katwate & P. Kumkar, 18 November 2015 ; ZRC 44030, 5 ex., 46.4–60.7 mm SL, South Andaman Island , Madhuban, India, coll. P. Biswas, 1 Oct 1997 ; ZRC 46955, 2 ex., 44.8–53.1 mm SL, Rutland Island off South Andaman Island, India, coll. P. Biswas, Mar 2001 .

Aplocheilus panchax : BNHS FWF 569 , 1 ex., 28.3 mm SL, Beri Baor , Ramnagar, Kolkata, West Bengal, India (22° 54' 32"N, 88° 51' 14" E, 5 m asl.), coll. U. Katwate, R. Raghavan and N. Dahanukar, 6 June 2014 ; BMNH 1934.10.17.92-96, 5 ex., 29.7–43.7 mm SL, Bengal, India, coll. B Das; Day’s material from Bengal: BMNH 1889.2.1.2095-2100, 6 ex., 35.9–45.2 mm SL, Calcutta , India, coll. F. Day.

Aplocheilus armatus : BMNH 1974.10.10.901-907, 7 ex., 28.1–40.8 mm SL, Ranu Lamongan , near Klakah , Java, Indonesia, coll. Green & Cobet & Watts ; Unregistered, 2 ex., Singapore, Sungai Poyan, coll. Heok Hui Tan, 9 May 2007 (only photographs examined)

Diagnosis. Aplocheilus andamanicus differs from all its congeners by the combination of the following characters: large-sized body (up to 74.8 SL and 92.8 mm TL); cephalic lateral line system incomplete, extending up to vertical through posterior margin of dorsal-fin base; 39–40 scales in longitudinal series; 11 scales in transverse row; 20–21 circumpeduncular scales; dorsal fin with 9–10 rays including 2–3 unbranched and 7 branched fin rays, posterior margin of dorsal fin rounded, short, not reaching vertical through caudal-fin base/posterior margin of hypural plate; pelvic fin short in mature males, with no prolonged fin rays, not extending beyond the vertical through anterior margin of anal-fin base; anal fin with nearly even height throughout its length; caudal-fin margin rounded; gill rakers 11–12 on first ceratobranchial; 6 branchiostegal rays; 33–34 total vertebrae including the posterior-most compound centrum, 13–14 pre-anal, 15 abdominal, 18–19 caudal and 21–22 pre-dorsal vertebrae; mature males with unique colour pattern comprising 6–7 longitudinal rows of large red dots on flank, becoming more irregular and forming denser pattern of red dots on caudal-fin base; dorsal fin yellow to saffron-coloured with large black spot at base; anal fin yellowish, with three longitudinal rows of more or less vertical red dots on its distal half; pectoral fin hyaline; pelvic fin yellow; caudal fin yellow, more reddish towards ventral periphery, with narrow black rim along its posterior margin.

Description. Large sized, elongated, stout and relatively deep-bodied “ Aplocheilus ” attaining a maximum size of at least 74.8 mm SL. For general shape and appearance see Fig. 1A–C & 2A–B . Morphometric and meristic data for topotypic specimens and meristic information for syntypes are provided in Table 1.

Body elongated, sub-cylindrical anteriorly, laterally compressed posteriorly, stout, moderately deeper than wide; body depth 1.3–1.6 times its width near base of pelvic-fin origin, standard length 4.1–4.7 times its depth. Predorsal contour almost straight in mature males, slightly convex in females, rising gradually to nape, then running steadily straight up to dorsal-fin origin; ventral profile convex up to posterior end of anal-fin base. Caudal peduncle broad, short, its length 1.1–1.9 times its depth, dorsal and ventral profile almost straight up to posterior end of hypural plate. Head large, stout, narrow, dorsoventrally flattened towards snout in lateral view, its length 1.7–2.0 times its depth. Mouth terminal, snout pointed, jaws large, lower jaw significantly larger than upper jaw, its length equal to or slightly larger than eye diameter. Eyes large, mid-laterally positioned, somewhat closer to snout tip than to posterior margin of operculum, eye diameter 0.5–0.7 times interorbital width.

Dorsal fin short, with rounded distal margin, originating on vertical between bases of 10th and 11th (2) branched anal-fin rays in males, 13th and 14th (5) in females and immature individuals; posterior margin separated distinctly from caudal-fin base and hypural plate, dorsal-fin length 1.6–1.9 times head length. Dorsal fin with 9–10 serially associated rays including 2 (5) or 3 (4) unbranched and 7 branched fin rays. Pectoral fin with 1 (2) or 2 (5) simple and 13 (1) or 14 (6) branched rays, its margin rounded, posterior margin extending beyond vertical through anterior third of pelvic fin. Pelvic fin with one simple and five branched rays, short, rounded, with no prolonged fin rays, nearly reaching vent when adpressed, but well-separated from anterior base of anal fin. Anal fin large, elongated, square, of nearly even height throughout its length, 1 (1) or 2 (6) supernumerary rays, two simple and 14 (5) or 15 (4) branched serially-associated rays; distal margin of anal fin straight, with rounded anterior and posterior extremities. Caudal fin rounded, with principal caudal-fin rays dorsally 7 (6) or 8 (3), ventrally 7 (3) or 8 (6) and 8 (6) or 9 (3) dorsal and 10 ventral procurrent rays.

Cephalic lateral-line system incomplete, extending up to vertical through posterior margin of dorsal-fin base. Scales small, cycloid covering entire body and head except ventral surface of head. Body squamation extending over anterior 25–30% of caudal fin. No scales on dorsal- and anal-fin bases. Frontal squamation arranged in triangular pattern, scale “E” medially overlapped, median scale “A” smaller than scale “B”. Longitudinal series of scales in mid-lateral scale row 39 (3) or 40 (4). Scales in transverse row between bases of dorsal and anal fin 11, circumpeduncular scales 20 (3) or 21 (4).

Cephalic neuromasts: supraorbital 4, parietal 2, anterior rostral 1, posterior rostral 1, anterior infraorbital 2, preorbital 1, median infraorbital 5, posterior infraorbital 2, otic 1, post-otic 2, supratemporal 1, preopercular 3+4, mandibular 2, lateral mandibular 4.

Total number of vertebrae 33(5)–34(4), with 15 abdominal and 18(5)–19(4) caudal vertebrae; 13(7)–14(2) preanal, and 21(7)–22(2) pre-dorsal vertebrae. Gill rakers on first branchial arch 1 +11 (1) –12 (1).

Coloration in life. Male. Body light brown with yellowish and pale-blue iridescence throughout head and flank. Dorsum dark brown with large iridescent silver spot on frontal squamation. Upper jaw dark brown, lower jaw deep reddish orange, extending up to anteroventral margin of eye. Iris dark brown on inner periphery, with light brown or iridescent yellow in dorsal half and deep blue patch in ventral ( Fig. 1C ) or posterior ventral half ( Fig. 1A–B ). Opercular region deep yellow with irregular red streaks or patches, preopercle and sub-opercular region iridescent pale blue. 6–7 longitudinal rows of distinct red dots between postorbital region and caudal-fin base; rows becoming more irregular with denser patterning of red spots on caudal-fin base and anterior one-fourth of caudal fin. Dorsal fin with large black spot at base, margin deep yellow or saffron. Anal fin with deep yellowish margin and three longitudinal rows of more or less vertically-elongate red dots on its distal half. Pectoral fin hyaline. Pelvic fin yellow. Anterior fourth of caudal fin scaled with mosaic of red dots, middle region hyaline, ventral periphery of caudal-fin base yellow or reddish, posterior margin with narrow black rim.

Female. Body light brown with moderate pale-blue iridescence on flank. Dorsum brown with large iridescent silvery spot on frontal squamation. Lower jaw and belly pale brown. Iris same colour as described for male. Opercular region with wide yellow spot, preopercle and sub-opercular region hyaline with indistinct blue shimmering. No longitudinal rows of red dots on flank. Dorsal fin with large black spot at base, margin yellow. Pectoral fin hyaline. Anal and pelvic fins with hyaline distal half and yellowish margin. Caudal fin mostly hyaline with indistinct saffron coloration at its periphery, margin with narrow black rim.

Coloration in preservative. Snout, head and dorsum dark brown. Lower lip, cheek, gill cover, area of superficially positioned cleithrum, lower head and abdominal region uniformly pale yellowish white in colour ( Fig. 2A, B ). Lateral body cream white with 6–7 rows of brown dots, becoming more irregular towards base of caudal peduncle and on anterior fourth of caudal fin. Iris and pupil black. Dorsal fin with broad black spot at base, distal part hyaline. Pectoral, pelvic, anal and caudal fins hyaline. Caudal fin margin with narrow black rim.

Genetic analysis. In both Bayesian and maximum-likelihood analysis of DNA-sequence data, A. andamanicus formed a distinct clade separate from A. panchax from India and from Southeast Asian specimens also assigned to A. panchax by Beck et al. (2017). We assign the sequences from specimens of Aplocheilus from southeast Asia to the species A. armatus (see notes on Odontopsis armata, below). Aplocheilus andamanicus was recovered as the sister group to a clade comprising A. panchax and A. armatus within the analysis of our limited Aplocheilus samples. Genetically A. andamanicus differs from A. panchax by a distance of 9.6–10.8% and from A. armatus by 12.3–13.6% ( Table 2).

Distribution. Topotypes of A. andamanicus were collected from the streams of Sholbay 14, south Andaman Island. Day’s specimens have “Port Blair” (which is on the southern Island) and “Andamans” as localities. Herre (1939) suggested that the distribution of Aplocheilus covered the north, middle and southern Andaman Islands. In our expedition to the Andaman and Nicobar Islands, we found this species only on the south Andaman Island, where it is abundant in streams and paddy fields. We did not encounter this species in the Nicobar Islands.

Remarks. Day (1870: 700), in his account “On the Fishes of the Andaman Islands” referred the specimens of Aplocheilus from the Andamans to Haplochilus panchax ( Hamilton, 1822) (now A. panchax ). He was nevertheless impressed by their “magnificent size at the Andamans, compared with what it attains in India ” already pointing out one of the key differences between island and Indian mainland populations. Subsequently, Day (1878: 523) mentioned that specimens of A. panchax from the Andaman Islands in the Bay of Bengal, differ from those available in Calcutta (within Bengal, the type locality) in the number of dorsal-fin rays (7–8 vs. up to 11). Herre (1939) agreed with Day’s (1870) characterisation, but his diagnosis of the Andaman specimens was based only on a comparison with specimens occurring in the Malay Peninsula from Singapore to Pinang (Penang), where he describes the Andaman species as “The largest Andaman examples are gigantic compared to those seen from Malaya and Ceylon ”.

Köhler (1906) disagreed with Day’s (1878) treatment of the Andaman Aplocheilus as panchax and considered them as a distinct species when he noted that “Ein Haplochilus mit 10 oder 11 Dorsalstrahlen ist entschieden kein Haplochilus panchax mehr.” (“A Haplochilus with 10 or 11 dorsal-fin rays is very clearly not a Haplochilus panchax anymore.”). As a consequence of his statement he proposed a new name, Haplochilus andamanicus , for Day’s (1878) panchax from the Andamans when he stated that “Die andamanische Form mit 11 Rückenflossenstrahlen, die Day nicht näher beschreibt, schalten wir dementsprechend als Haplochilus andamanicus (zunächst hypothetisch) aus.” (“The Andamanian form with 11 dorsal-fin rays, which Day does not describe in more detail, we exclude therefore as Haplochilus andamanicus (initially hypothetically).” Köhler (1906) also mentioned that he could verify the fin rays counts when he could get specimens from the Andamans (“Vielleicht ist es mir möglich, auch von dorther Spiritusexemplare zu erhalten, um die Frage endgültig entscheiden zu können”.).

There has been disagreement regarding the availability of Köhler’s (1906) name, Haplochilus andamanicus . Eschmeyer et al., (2017) considered this name unavailable, whereas Kottelat (2013) treated it as an available name but considered the identity of A. andamanicus as doubtful.

Eschmeyer et al. ’s (2017) argument for treating A. andamanicus as an unavailable name was given as “…clearly not proposed as a species by Köhler 1906, but for the time being 'hypothetically excluded until specimens are available'.” This is actually an incorrect translation of Köhler’s (1906) statement, which is quoted in full above. Köhler clearly proposed andamanicus as a new species name, indicating Day’s (1878) information, which is further supported by Köhler’s (1906) statement that A. andamanicus is clearly not a panchax anymore. His reference to a hypothetical consideration refers to the fact that he, Köhler, would want to verify Day’s reported high dorsal-fin ray counts. We thus agree with Kottelat (2013), who considered ‘ A. andamanicus’ an available name and treat Day’s material of this fish from the Andamans as syntypes. Of these we have selected the largest specimen of BMNH 1870.5.18.34-36, as lectotype, which also fixes the type locality to Port Blair on the southern Andaman island.

Comparison of freshly-collected topotypic specimens of A. panchax from Bengal and A. andamanicus from the Andamans, and Day’s material in the collections of the Natural History Museum, London, revealed significant morphological and genetic differences necessitating the revalidation of the latter. Aplocheilus andamanicus differs from topotypic A. panchax by the combination of the following characters: the most discussed ( Day, 1878; Köhler 1906; Herre, 1939) being body size difference, A. andamanicus grows much larger in size (it is probably the largest Aplocheilus in South and South-East Asia), to at least 74.8 mm SL (vs. smaller in size); 9–10 dorsal-fin rays (vs. 6–8); 15 principal and 18–19 procurrent caudal-fin rays (vs. 12–13 principal and 12 procurrent caudal-fin rays); dorsal fin with posterior margin widely separated from caudal-fin base or hypural plate (vs. extending beyond vertical through caudal base or hypural plate); pectoral fin extending beyond vertical through anterior one-third of pelvic fin (vs. pectoral fin extending to half the length of pelvic fin); pelvic fin nearly reaching vent when adpressed but well separated from anterior base of anal fin (vs. pelvic fin extends beyond vent reaching anterior base of anal fin); caudal-fin margin rounded (vs. more oval in) ( Fig. 3 ); lateral line system incomplete extending up to the vertical from posterior margin of dorsal fin base (vs. lateral line system complete, reaching caudal-fin base); total vertebrae 33–34 (vs. 28–30); pre-anal vertebrae 13–14 (vs. 11–12); caudal vertebrae 18–19 (vs. 14–16); median scale “A” of frontal squamation pattern smaller than scale “B” (vs. median scale “A” significantly larger than scale “B”) ( Fig. 3 ); single anterior rostral and posterior rostral neuromasts (vs. 2 anterior rostral and 3 posterior rostral neuromasts). Day (1878) reported a total of up to 11 dorsal-fin rays in his Andaman collection, a character that was subsequently used by Köhler (1906) to diagnose A. andamanicus . Radiographs of Day’s collection (syntypes, BMNH 1889.2.1.2107-2110) and cleared and stained topotypes (BNHS FWF 384 & 385) of A. andamanicus showed, however, only 9–10 dorsal-fin rays. In any case, the dorsal-fin ray count is still valid and is the most significant diagnostic character that distinguishes A. andamanicus from A. panchax (9–10 vs. 7–8).

Furthermore, A. andamanicus can easily be distinguished from A. panchax based on its unique coloration pattern including, dorsal fin extremity deep yellow or saffron (vs. blue in A. panchax ); distal half of anal fin hyaline in female or studded with three longitudinal rows of vertically elongated red dots (vs. distal half of anal fin deep iridescent blue); pelvic fin yellow (vs. hyaline in A. panchax ); and caudal fin periphery hyaline or subtle red (vs. deep iridescent blue in A. panchax ). Both species are also genetically distinct, with a cox1 distance of 9.6–10.8% ( Table 2).

Not only does Aplocheilus andamanicus differ in numerous characters from A. panchax , it can also be easily distinguished from other mainland Indian and Sri Lankan species, including A. blockii Arnold, 1911 , A. dayi Steindachner, 1892 , A. kirchmayeri Berkenkamp & Etzel, 1986 , A. lineatus ( Valenciennes, 1846) , A. parvus ( Sundara Raj, 1916) and A. werneri Meinken, 1966 , by the combination of the following characteristics: mouth terminal in A. andamanicus (vs. inferior with protruding lower jaw in A. blockii and A. parvus ); dorsal fin short, widely separated from vertical through caudal-fin base or hypural plate (vs. dorsal fin long elongated in A. blockii , A. kirchmayeri and A. parvus , posterior tip extending beyond vertical through caudal-fin base onto caudal fin); pelvic fin short, its rays not elongated (vs. long, its rays elongated in A. lineatus ); flank without any dark vertical bars or markings (vs. body with broad or narrow dark bars in A. lineatus , A. dayi and A. werneri ).

Figures

FIGURE 1. Topotypes of Aplocheilus andamanicus and A. panchax in life. (A) Aplocheilus andamanicus, male, BNHS FWF 563, 65.2 mm SL, (B) A. andamanicus female, BNHS FWF 562, 65.0 mm SL, (C) A. andamanicus, female, BNHS FWF 564, 30.8 mm SL, and (D)A. panchax, male, BNHS FWF 569, 28.3 mm SL.

FIGURE 3. Diagnostic characters separating Aplocheilus andamanicus and A. panchax. (A) Diagrammatic representation of the frontal squamation pattern and neuromasts and (B) structural morphology and coloration pattern of caudal fin in Aplocheilus andamanicus (BNHS FWF 563) and A. panchax (BNHS FWF 569). Abbreviations: ais = anterior infraorbital series; an = anterior naris; arn = anterior rostral neuromast; ots = otic series; pan = parietal neuromast; pbs = preorbital series; pis = posterior infraorbital series; pn = posterior naris; prn = posterior rostral neuromast; sos = supraorbital series; stn = supratemporal neuromasts; A–F = frontal scales.

FIGURE2. Diagnostic characters for separating Aplocheilusandamanicus and A.panchax. (A) One of the originalsyntypes of Aplocheilus andamanicus collected by Day (1878) from the Andamans, now lectotype, BMNH 1870.5.18.34-36, 74.8 mm SL, Port Blair, (B) topotypes of A. andamanicus, male, BNHS FWF 563, 65.2 mm SL, collected from south Andaman Island, (C) topotypes of A. panchax, male, BNHS FWF 569, 28.3 mm SL, collected from West Bengal, India. See-through vertical lines represent the relative positions of the pectoral-fin origin and the posterior extremity of dorsal, pelvic and anal fins.