Kryptopterus vitreolus

Ng, Heok Hee & Kottelat, Maurice, 2013, After eighty years of misidentification, a name for the glass catfish (Teleostei: Siluridae), Zootaxa 3630 (2), pp. 308-316 : 309-312

Kryptopterus vitreolus

( Figs. 1 , 2 , 5 a)

Kryptopterus bicirrhis (non Valenciennes)—Vidthayanon, 2002: 69.

Type material. Holotype: UMMZ 249801, 45.2 mm SL; Thailand: Trat Province, Amphoe Khao Saming; K. Udomritthiruj, 27 November 2011.

Paratypes: UMMZ 249802 (12), 38.8–49.1 mm SL; data as for holotype. CMK 18688 (18), 15.5–39.3 mm SL; Thailand: Trat Province, northwest of Khao Saming; M. Kottelat & K. Kubota, 17 July 2005. UMMZ 249804 (9), 39.7–42.4 mm SL; Thailand: Phatthalung Province, Amphoe Khoa Chai Son, Tambon Khao Chai Son; K. Udomritthiruj, 3 February 2012. CMK 10731 (10), 21.1–32.7 mm SL; ZRC 35719–35724 (6), 25.4–29.2 mm SL; Thailand: Phatthalung Province, Thale Noi; K. Kubota, December 1993. ZRC 37586 (2), 52.4–53.3 mm SL; Thailand: Nakhon Si Thammarat Province, Nakhon Si Thammarat; collector unknown, 21 August 1981. UMMZ 249803 (12), 31.4–39.3 mm SL; Thailand: Nakhon Si Thammarat Province, Ampoe Tha Sala, Baan U-Tapao, 8°37'40.9"N 99°55'39.0"E; K. Udomritthiruj, 30 December 2011. CMK 12193 (12), 31.8–64.6 mm SL; Thailand: Narathiwat Province, Mae Nam Tod Daeng, about 6 km N of Narathiwat; K. Kubota, 10 November 1995. ZRC 39288 (8), 38.3–62.8 mm SL; Thailand: Narathiwat Province, Mae Nam Sungai Kolok; K. Kubota, December 1995.

Diagnosis. Kryptopterus vitreolus can be distinguished from all other congeners (except K. minor and K. piperatus ) in having a transparent (vs translucent or opaque) body in life, and from members of the K. cryptopterus , K. limpok , and K. schilbeides groups in having fewer anal-fin rays (48–55 vs. 64–85). Kryptopterus vitreolus can be distinguished from members of the K. bicirrhis species group ( K. bicirrhis , K. lais , K. macrocephalus , K. minor , K. palembangensis and K. piperatus ) in having the following combination of characters: snout length 29–35% HL, eye diameter 28–34% HL, body depth at anus 16–20% SL, depth of caudal peduncle 4–7% SL, maxillary barbels reaching beyond base of first anal-fin ray, dorsal profile with pronounced nuchal concavity, 14–18 rakers on first gill arch, and 48–55 anal-fin rays.

Description. For biometric data see Table 1 . Body and head laterally compressed. Dorsal profile slightly humped with a distinct nuchal concavity; descending gently from anterior quarter of body to snout tip, and from anterior quarter of body to caudal peduncle. Anterior profile of snout rounded. Anterior pair of nostrils tubular, anteromedial to maxillary-barbel base. Posterior pair of nostrils bordered by fleshy dorsal and ventral membranes, posteromedial to maxillary barbel base.

Mouth terminal, gape slightly oblique. Rictal fold present but poorly developed, consisting of upper lobe joined at corner of mouth with lower lobe, subtended by short submandibular groove.

Teeth villiform. Dentary teeth in slightly curved, in elongate bands narrowing posteriorly, reaching from symphysis almost to mouth corners; premaxillary teeth in broader, slightly curved rectangular bands; palatal teeth in a single median ovoid patch.

Two pairs of barbels. Maxillary barbels slightly flattened for entire length, reaching to fifth anal-fin ray. Mandibular barbels very short, approximately one quarter of eye diameter.

Eyes of moderate size, subcutaneous; located in middle of head; visible dorsally and ventrally. Gill membranes separate, overlapping, free from isthmus. Branchiostegal rays 8 (30). Gill rakers short, anteriormost rakers on lower first arch small, widely spaced; 3+11 (6), 3+12* (16), 3+13 (4), 4+12 (2) or 3+15 (2).

Dorsal fin rudimentary, with ii (30) short, poorly-ossified rays. Depressed pectoral fin to base of seventh analfin ray; distal margin broadly convex, with rounded tip. Third branched pectoral ray longest; fin with I,8* (8), I,9 (20) or I,10 (2) rays. Proximal two-thirds of first pectoral-fin element co-ossified into a spine. Distal margin of pelvic-fin convex, with i,5 (30) rays. Distal margin of anal fin straight, with 48 (2), 49 (2), 50* (3), 51 (6), 52 (5), 53 (4), 54 (6) or 55 (2) rays; separate from caudal fin. Integument over anal fin thickened proximally for slightly more than half of ray lengths; fin-ray erector muscles extending along anterior edges of anal-fin rays, ventralmost extent of muscles that of thickened integument. Caudal peduncle slender. Caudal fin strongly forked; principal rays i,7,8,i (30).

Lateral line complete, extending to middle of caudal-fin base. Urogenital papillae of both sexes located immediately posterior to insertions of pelvic fins. Vertebrae 10+34=44 (2), 10+35=45* (13), 10+36=46 (12), 10+37=47 (2) or 11+36=47 (1).

Coloration. In 70% ethanol: Body and head dark yellow. Base of maxillary barbel and infraorbital region with dense aggregation of melanophores. Dorsal surface of snout and ethmoidal region with dense aggregation of melanophores; in latter case visible as two parallel dark bands running along dorsolateral surfaces of head. Dorsal midline of body with densely-spaced melanophores running along entire length of body; melanophores spreading out to flank above lateral line, becoming more diffuse there. Humeral region with dense aggregation of melanophores forming a dark spot. A very narrow, dark longitudinal streak along lateral line formed by a single row of melanophores. Proximal quarter of principal caudal-fin rays with a single row of melanophores, causing dusky appearance to caudal-fin base. Base of first anal-fin ray with dense aggregation of melanophores, causing dark appearance to urogenital region. Ventral surfaces with very diffuse scattering of melanophores, with denser aggregation in abdominal region in some individuals. Pectoral spine dark. Proximal and distal elements of anal-fin pterygiophores outlined in black. Pectoral- and anal-fin rays with scattered melanophores; other fin rays hyaline. All fin-membranes hyaline. Base of maxillary barbel with dense aggregation of melanophores, causing dark appearance; melanophores becoming more diffuse towards distal tip of barbel.

Coloration in life similar, except for transparent body with silvery visceral area. Dorsal surfaces of head and body often with yellowish tint. Spinal cord visible as distinct dark longitudinal line. Neural and hemal spines, as well as both proximal and distal elements of anal-fin pterygiophores outlined in black, clearly visible ( Fig. 2 ).

Distribution. Known from the short, coastal drainages in peninsular Thailand debouching into the Gulf of Thailand south of the Isthmus of Kra (from about 8°38'N to 6°2'N), as well as similar rivers draining the southeastern face of the Khao Banthat (Cardamom) Mountains in southeastern Thailand ( Fig. 3 ). Emmens & Axelrod (1966) report this species from the vicinity of Penang, but this record requires verification.

Kryptopterus vitreolus has been observed in slow moving to standing, brown to black, water. Its disjunct distribution in the Malay Peninsula and Southeastern Thailand and absence in central Thailand is shared with a number of genera and species typical of the Sundaic fish fauna (e.g. Trigonostigma , Trigonopoma , Barbucca , Vaillantella ) (Kottelat, 1989).

Etymology. From the diminutive form of the Latin adjective vitreus, meaning of glass, in reference to the transparent appearance of this species in life (which gives this species its common name of glass catfish).

Figures

FIGURE 1. Kryptopterus vitreolus, holotype, UMMZ 249801, 45.2 mm SL; Thailand: Trat Province, Amphoe Khao Saming.

FIGURE 2. Kryptopterus vitreolus, live specimen (about 50 mm SL) from southern Thailand showing transparent appearance in life (specimen not preserved). Photograph courtesy of Johnny Jensen.

FIGURE 3. Map showing distributions of all three species of Kryptopterus that are transparent in life.

FIGURE 5. Lateral views of heads and predorsal regions of: a. Kryptopterus vitreolus, UMMZ 249804, 42.3 mm SL; b. K. minor, CMK 10447, 42.2 mm SL, showing pronounced nuchal concavity (indicated with arrow) in the former. Images not to scale.

Tables

TABLE 1. Biometric data for Kryptopterus vitreolus (n = 30).

	Holotype UMMZ 249801 Range	Mean±SD
Standard length (mm)	45.2 31.4–64.6
%SL
Predorsal length	25 24–27	25.5±1.1
Preanal length	29 26–31	28.0±1.5
Prepelvic length	26 24–29	26.1±1.5
Prepectoral length	19 18–21	19.6±1.1
Length of anal-fin base	74 68–78	72.6±2.7
Pelvic-fin length	4 4–6	4.5±0.6
Pectoral-fin length	14 14–20	17.0±1.6
Pectoral spine length	11 9–12	10.5±1.0
Caudal-fin length	21 18–23	20.1±1.5
Body depth at anus	16 16–20	18.3±1.4
Depth of caudal peduncle	4 4–7	5.8±0.8
Head length	17 16–19	17.9±0.9
Head width	9 8–11	9.1±0.7
Head depth	12 11–14	12.3±0.8
%HL
Snout length	35 29–35	32.5±2.0
Interorbital distance	42 39–44	41.5±1.6
Eye diameter	31 28–34	31.8±1.8
Maxillary barbel length	250 213–343	267.2±43.3
Mandibular barbel length	6 6–12	7.7±3.4