Tonlesapia amnica, Ng, Heok Hee & Rainboth, Walter J., 2011

Ng, Heok Hee & Rainboth, Walter J., 2011, Tonlesapia amnica, a new species of dragonet (Teleostei: Callionymidae) from the Mekong delta, Zootaxa 3052, pp. 62-68 : 63-65

Tonlesapia amnica , sp. nov.

( Figs. 1–3 )

Type material. Holotype: UMMZ 246104, 37.6 mm SL; Vietnam: An Giang Province, Song Hau Giang (=Bassac River), 4 km downstream from Long Xuyen, 10°20'N 105°29'E; W. J. Rainboth, 18 April 1999.

Paratypes: UMMZ 218042 (2), 31.0– 34.3 mm SL; Vietnam: Vinh Long Province, Kinh Thuy Cai canal 10 km E of Vinh Long, at mouth of canal into Mekong River; R. P. Weidenbach & W. J. Rainboth, 21 June 1974. UMMZ 218069 (2), 21.2–36.0 mm SL; Vietnam: Vinh Long Province, Kinh Thuy Cai canal 10 km E of Vinh Long, at mouth of canal into Mekong River; R. P. Weidenbach & W. J. Rainboth, 21 June 1974. UMMZ 218122 (53), 13.6– 33.4 mm SL; Vietnam: Vinh Long Province, fish market at Vinh Long; W. J. Rainboth, 22 June 1974. UMMZ 224623 (1), 37.2 mm SL; Vietnam: An Giang Province, Song Hau Giang (=Bassac River), 3 km downstream from Chau Doc; R. E. Arden & O. K. Minh, 13 October 1974. UMMZ 224681 (2), 13.4–37.4 mm SL; Vietnam: Can Tho Province, Song Hau Giang (=Bassac River) canal heading NW from Can Tho ferry crossing; W. J. Rainboth & R. P. Weidenbach, 18 July 1974. UMMZ 224709 (5), 16.1–33.7 mm SL; Vietnam: An Giang Province, Mekong River at Long Xuyen; R. P. Weidenbach, 24 July 1974. UMMZ 224714 (8), 15.4–34.5 mm SL; Vietnam: An Giang Province, W side of Mekong River, 2 km S of Tan My; R. P. Weidenbach, 24 July 1974. UMMZ 227238 (10), 18.0–32.0 mm SL; Vietnam: Can Tho Province, Mekong River from Can Tho ferry to town of Can Tho, along S bank; R. P. Weidenbach & M. L. Smith, 15 July 1974. UMMZ 245375 (8), 28.7–43.0 mm SL; data as for holotype. UMMZ 245589 (2), 40.2–43.3 mm SL; Vietnam: Vinh Long Province, Song Co Chien, 3–4 km downstream from Vinh Long, 10°15'N 106°7'E; W. J. Rainboth, 13 April 1999. UMMZ 245590 (12 alc., 1 c&s), 33.0–49.0 mm SL; Vietnam: Can Tho Province, Song Hau Giang (=Bassac River), side channel downstream from Can Tho, 10°1'N 105°47'E; W. J. Rainboth, 22 March 1999. UMMZ 245591 (1), 35.0 mm SL; Vietnam: Can Tho Province, Song Hau Giang (=Bassac River), 3 km downstream from Can Tho, 10°1'34"N 105°48'8"E; W. J. Rainboth, 17 March 1999. UMMZ 246105 (1), 20.8 mm SL; Vietnam: An Giang Province, Song Chau Doc 3 km upstream from Chau Doc, 10°45'N 105°7'E; W. J. Rainboth, 19 April 1999.

Diagnosis. Tonlesapia amnica differs from its only congener, T. tsukawakii , in having the infraorbital canal extending beyond (vs. not reaching) ventral margin of orbit, a more slender body (7.2–13.5% SL vs. 14.3–15.0) and caudal peduncle (4.4–5.2% SL vs. 5.1–6.3), a smaller eye (6.5–8.3% SL vs. 8.7–9.2) and more dorsal-fin rays (9–10 vs. 8).

Description. D 2 viii,1* (21) or ix,1 (1); A vi,1 (2) or vii,1* (22); P 1 i,12, i (6), i,12,ii (1), ii,12,ii (1), i,13,i* (6), i,14,i (4), i,15,i (3) or i,17,i (1); P 2 i,5 (22); C i,6,ii (22). Biometric data as in Table 1 . Body elongate, slightly depressed. Head moderately depressed. Snout sloping evenly and moderately. Dorsal body profile somewhat horizontal to base of second dorsal fin, sloping gradually ventrally from there to end of caudal peduncle. Ventral body profile horizontal to base of first anal-fin ray, sloping very gently dorsally from there to end of caudal peduncle.

Eye large. Interorbital space narrow. Gill opening small, ovoid, located midway between posteriormost point of orbit and base of first pectoral-fin ray. Preopercular spine without antrorse spur at base, with posterior main tip curved dorsally, and 3–7 curved points along dorsal margin; spine covered by thin skin along dorsal margin. Upper jaw protractile, posterior end reaching to midway between anterior tip of mesethmoid and anteriormost point of orbit. Single nostril on snout. Urogenital papilla conical, males with slightly longer papilla than females. Lateral line extending from eye to proximal quarter of third branched caudal-fin ray. Cephalic lateralis system poorly developed and indistinct, consisting of branched supraorbital canal, unbranched infraorbital canal extending beyond ventral margin of orbit and very short preoperculo-mandibular canal with single antrorse branch ( Fig. 2 ). Lateral line on each side of body connected to each other via transverse branch across occipital region and dorsal commissure across caudal peduncle.

First dorsal fin absent, but three pterygiophores present. Distal margin of second dorsal fin straight. Fin rays simple except for last ray, which is divided at base. Anal fin origin at vertical through base of second fin ray of second dorsal fin; distal margin of anal fin straight. Pelvic fin with convex distal margin, reaching to vertical through base of third fin ray of second dorsal fin. Pectoral fin with convex distal margin, reaching vertical through base of fourth fin ray of second dorsal fin. Caudal fin not sexually dimorphic, without elongate median rays in males.

Coloration. In 70% alcohol: head and body dark yellow, fading to lighter color ventrally. Dorsal and lateral surfaces of head and body with numerous small blackish spots distributed regularly in longitudinal series. Dense aggregation of melanophores on cheeks, imparting brown coloration on them. A longitudinal series of dark blotches present on flanks immediately below lateral line, each blotch being comprised of large scattered melanophores. Dark spots and blotches less distinct in some individuals. Fin membranes of all fins hyaline; rays of all fins with scattered small melanophores (denser in dorsal-fin rays of some individuals), imparting slightly dusky appearance to all fins.

Coloration in life similar, but with lighter ground color and more pronounced dark pigmentation ( Fig. 3 ).

Etymology. The specific name amnica is a feminine Latin adjective meaning pertaining to a river. The name is used in reference to the riverine habitat of this species.

Distribution and habitat. Known from the Mekong River delta in southern Vietnam ( Fig. 4 ). The Song Hau Giang (a branch of the Mekong River also known as the Bassac River) at the type locality of C. amnica is fairly clear, slow flowing (current about 0.2 ms -1) and wide (2 km) with a sand and silt bottom. Other species of fish obtained at this locality included: Clupeoides borneensis (Clupeidae) , Corica soborna (Clupeidae) , Coilia lindmani (Engraulidae) , Thryssocypris tonlesapensis (Cyprinidae) , Acantopsis sp. ( Cobitidae ), Kryptopterus geminus (Siluridae) , Pangasius mekongensis (Pangasiidae) , Akysis similis (Akysidae) , Plotosus canius (Plotosidae) , Boesemania microlepis (Sciaenidae) , Polynemus bidentatus (Polynemidae) , Eleotris melanosoma (Eleotrididae) , Redigobius chrysosoma (Gobiidae) , Stenogobius mekongensis (Gobiidae) , Taenioides cirratus (Gobiidae) , Brachirus elongatus (Soleidae) , Synaptura panoides (Soleidae) , Cynoglossus gracilis (Cynoglossidae) and Cynoglossus puncticeps (Cynoglossidae) . Tonlesapia amnica has also been collected from brackish habitats and is the third species of Indo-Pacific callionymid known to inhabit freshwaters (the other species being Callionymus fluviatilis and T. tsukawakii ).

Figures

FIGURE 1. Tonlesapia amnica, UMMZ 246104, holotype, 37.6 mm SL; dorsal, lateral and ventral views.

FIGURE 2. Dorsal, lateral and ventral views of head of Tonlesapia amnica (UMMZ 245375, paratype, 37.9 mm SL), showing cephalic lateralis system. Scale bar represents 2 mm.

FIGURE 3. Tonlesapia amnica, UMMZ 245589, paratype, 43.3 mm SL; dorsal and lateral views showing coloration in life.

FIGURE 4. Map of the Mekong River drainage, showing collection localities of Tonlesapia amnica and T. tsukawakii.

Tables

TABLE 1. Biometric data for Tonlesapis amnica (n = 22).

	Holotype	Range	Mean±SD
%SL
Predorsal (2) length Preanal length	55.1 53.5	45.5–55.1 49.3–58.2	50.4±3.24 53.5±2.74
Prepelvic length	21.5	21.6–26.3	23.7±1.54
Length of dorsal-fin base	32.5	28.8–35.9	32.3±1.95
Length of anal-fin base	33.6	29.3–36.6	33.2±2.48
Pectoral fin length	28.6	22.7–28.6	25.6±1.53
Pelvic fin length	27	24.2–29.4	26.6±1.76
Caudal fin length	25.5	21.3–26.6	23.9±1.54
Caudal peduncle length	16.3	13.9–18.8	16.6±1.37
Caudal peduncle depth	4.7	4.4–5.2	4.8±0.28
Body depth	13.4	7.2–13.5	11.0±2.03
Body width	21	14.2–22.5	19.5±2.30
Head length	24.7	21.3–24.7	23.8±1.11
Preorbital length	6.3	5.6–6.5	6.1±0.32
Eye diameter	7.6	6.5–8.3	7.5±0.51
Interorbital distance	2.6	1.8–2.8	2.3±0.31
Maxillary length	7.3	5.9–7.3	6.8±0.40
Preopercular spine length	12.6	9.5–13.3	11.2±1.36