Nandus andrewi, Ng, Heok Hee & Jaafar, Zeehan, 2008

Ng, Heok Hee & Jaafar, Zeehan, 2008, A new species of leaf fish, Nandus andrewi (Teleostei: Perciformes: Nandidae) from northeastern India, Zootaxa 1731, pp. 24-32 : 25-29

Nandus andrewi sp. nov.

( Figs. 1 , 2 a, 3)

Type material. Holotype. ZRC 50364, 125.0 mm SL; India: West Bengal, Nadia district, Ichamati River drainage in the vicinity of Duttaphulia (23°14'N 88°43'E); A. Rao, 2 April 2003.

Paratypes. CAS 224164 (2), 86.3–93.9 mm SL; UMMZ 247483 (2), 77.3–78.0 mm SL; ZRC 50365 (2), 94.1–104.2 mm SL; locality as for holotype; A. Rao, April 2005. ZRC 50366 (2), 66.1–74.5 mm SL; data as for holotype.

Non-type material. ZRC 50367 (7), 32.3–101.4 mm SL; ZRC 50374 (5), 51.8–82.8 mm SL; locality as for holotype; A. Rao, April 2005. ZRC 51108 (1), 56.0 mm SL; locality as for holotype; A. Rao, November 2004.

Diagnosis. Nandus andrewi is distinguished from all congeners by having a pale bluish-white (vs. mottled brown) body in life. It further differs from the only South Asian congener, N. nandus in having a more slender body (24.3–29.1% SL vs. 28.2–34.3), shorter pelvic fin (16.2–18.9% SL vs. 18.0–21.2). Nandus andrewi is further distinguished from N. nebulosus , N. oxyrhynchus and N. prolixus in having (vs lacking) a dark spot on the caudal peduncle, 45–52 (vs. 24–37) lateral line scales, and a more slender body (24.3–29.1% SL vs. 30.7– 44.1).

Description. Morphometric data as in Table 1 , meristic data as in Table 2 . Body compressed, moderately elongate; dorsal profile with slight, but noticeable concavity in interorbital region. Snout profile acute. Mouth moderately large, protrusible. Posterior end of maxilla extending just beyond vertical through middle of orbit. Eye moderately large, diameter about one fifth of head length. Posterior edge of preopercle with fine serrations. Gill rakers short and club-shaped, bearing pointed apical denticles. Teeth short, unicuspid, closely set and in many irregular rows on both upper and lower jaw.

Lateral line divided into two segments, with anterior segment more dorsally located than posterior segment. Upper lateral line beginning at dorsal origin of operculum, rising for distance equivalent to two or three scales rows and reaching greatest height above pectoral fin, thereafter sloping ventrally and ending at vertical through middle of anal-fin base (at 45th–52nd scale). Lower lateral line beginning at vertical through anterior third of anal-fin base, vertically centered along length of caudal peduncle and continuing slightly past end of hypural plate.

Scales ctenoid, imbricate, and nearly uniform in size throughout body. Scales present throughout cheek region, preopercle, opercle, and area around eye, absent along midline of interorbital region. Area around nares and upper lip scaleless. Gular region and ventral region of head immediately adjacent scaleless; sensory pores present in this region. Sheath of scales surrounding proximal regions of dorsal and anal fins, forming ridges along sides of hard rays and attached to soft-fin rays. Caudal fin scaled for about one quarter of length.

Dorsal fin with long base, anterior insertion anterior to vertical through posteriormost extent of opercle and posterior insertion at vertical through base of last anal-fin ray. Pectoral-fin origin anterior to pelvic-fin origin and shorter than pelvic fin. Pelvic fins not reaching urogenital opening or anterior insertion of anal fin. Longest ray of anal fin not reaching vertical through base of caudal fin.

Coloration. In 70% ethanol: base colour of head and body off white, central part of most scales on body greyish-brown, imparting overall greyish-brown colour to body. Greyish brown colour typically darker on dorsal one-quarter of body, and on scattered patches of scales on flanks posterior to pectoral-fin base (imparting slightly mottled appearance in some individuals). Dark wedge-shaped marking on sides of head originating from orbit and extending to opercle. Faint, dark band extending from anterior edge of orbit to tip of snout. Another faint dark band extending dorsoposteriorly from dorsoposterior orbital margin, merging with dark dorsum. Dark spot present on middle of caudal peduncle (fainter in some individuals). First 4–6 dorsal spines and membranes in between dark greyish-brown. Distal edges of membranes following spinous dorsal fin dark greyish-brown; rest of fin membrane hyaline and rest of fin spines light greyish-brown. Pectoral- and caudalfin rays light greyish-brown; fin membranes hyaline. Proximal two-thirds of pelvic fin dark greyish-brown; distal one third hyaline. Membranes between anal-fin spines typically dark greyish-brown; soft anal-fin rays light greyish-brown, fin membranes between soft rays hyaline. Live colour similar, but with bluish-white base colour and greyish-brown colour less pronounced ( Fig. 3 ).

Distribution. Currently only known from the Ichamati River drainage in northeastern India ( Fig. 4 ). The Ichamati River (not to be confused with a tributary of the Brahmaputra River with a similar name in Bangladesh) is a tributary of the Hooghly River, itself part of the Ganges River drainage.

Etymology. This species is named after Andrew Arunava Rao in recognition of his discovery of this new species and assistance to the authors during their field work in India.

Nandus species are typically distinguished by their snout shapes ( Fig. 2 ), although the differences in snout shape among N. andrewi , N. nandus and N. prolixus are not as pronounced as that among N. andrewi , N. nebulosus , and N. oxyrhynchus . Nandus andrewi can still be distinguished from N. nandus and N. prolixus by other morphological and colour characters as outlined in the diagnosis.

Nandus andrewi occurs sympatrically with N. nandus (although we lack information as to whether the two species occur syntopically), so the possibility of the former being a colour mutant of the latter was closely investigated. Our comparison of key morphometric values of N. nandus from the Ichamati River drainage (ZRC 51105; ZRC 51107) and N. andrewi supports the differences as stated in the diagnosis: N. nandus from the Ichamati River drainage have consistently deeper bodies (31.4–34.3% SL vs. 24.3–29.1), and longer pelvic fins (18.0–20.4% SL vs. 16.2–18.9) than N. andrewi . We also found additional morphological characters in addition to those listed in the diagnosis to distinguish the two species: the posterior edge of the preopercle in N. andrewi is more poorly-serrated than in N. nandus . Although this difference is obvious in specimens of ca. 105 mm SL and smaller, it is no longer distinct between the largest specimens of N. andrewi (125 mm SL) and N. nandus (117 mm SL) examined.

We have examined a large series of other Nandus species (particularly N. nandus , N. nebulosus and N. oxyrhynchus ) to investigate colour variation in congeners. Although we note that some individuals of N. nandus adopt a very pale colour, especially when stressed (becoming a more golden brown), the dark mottling is still evident in such specimens, even if the contrast between it and the rest of the body is much poorer. We conclude that there is little colour variation within (and even among) all other congeners, and that the pronounced colour difference between N. andrewi and all other congeners is indeed a species-specific character.

Figures

FIGURE 1. Nandus andrewi, holotype, ZRC 50364, 125.0 mm SL; India: West Bengal, Ichamati River.

FIGURE 2. Lateral views of heads of: a. Nandus andrewi, UMMZ 247483, paratype, 77.3 mm SL; b. N. nandus, UMMZ 247483, 80.0 mm SL; c. N. nebulosus, CAS 49450, 80.6 mm SL; d. N. oxyrhynchus, UMMZ 195557, 70.0 mm SL and e. N. prolixus, FMNH 51964, paratype, 81.3 mm SL.

FIGURE 3. Live coloration of Nandus andrewi (specimen ca. 60 mm SL, not preserved). Photograph courtesy of Erwin Schraml.

FIGURE 4. Map showing type locality of Nandus andrewi.

Tables

TABLE 1. Morphometric data for Nandus andrewi (n = 22).

	Holotype	Range	Mean±SD
In % SL
Predorsal length	42.3	40.2–43.1	41.7±0.9
Preanal length	72.9	72.9–78.1	75.6±1.8
Prepelvic length	41.7	41.0–44.2	42.7±1.0
Prepectoral length	36.8	36.4–43.0	39.8±1.5
Length of dorsal-fin base	56.9	46.1–56.9	51.0±2.4
Length of anal-fin base	15.5	12.4–15.8	13.7±1.1
Pelvic fin length	16.2	16.2–18.9	17.9±0.9
Pectoral fin length	17.9	15.1–18.5	17.0±1.2
Caudal fin length	24.2	21.5–28.5	24.9±2.2
Body depth	29.2	24.3–29.2	26.9±2.0
Caudal peduncle depth	11.8	8.9–11.8	10.4±0.9
Caudal peduncle length*	12.2	9.0-13.2	11.1±1.0
Head length	36.3	36.3–44.4	41.6±1.8
Head width	17.6	13.2–17.6	14.5±1.5
Head depth*	20.4	19.0-24.9	21.5±1.4
In % HL
Snouth length*	28.9	25.8–31.7	28.6±1.9
Interorbital distance	16.5	13.1–16.9	14.4±1.2
Eye diameter	20.5	18.2–21.7	20.2±1.1
* n=15

TABLE 2. Meristic data for Nandus andrewi (n = 22).

	Holotype	Range
Scale counts
LL, anterior	36	30–38
LL, posterior	18	10–18
above LL	6	4–6
below LL	15	15–17
circumpeduncular	21	18–21
predorsal	17	15–17
Fin-ray counts
dorsal	XIII,13	XII-XIV,11–14
pectoral	16	14–16
pelvic	I,5	I,5–6
anal	III,8	III,7–8
caudal	15	14–16
branchiostegal*	6	5–6
ceratobranchial*	2	2–3
epibranchial	8	8–10
vertebral centra	24	23–24
*n=14.
Discussion