Gavialiceps taiwanensis ( Chen & Weng, 1967 )

Lin, Chien-Ting & Ho, Hsuan-Ching, 2018, Morphological and molecular identification of leptocephali of Taiwanese duckbill conger, Gavialiceps taiwanensis (Chen & Weng, 1967) (Family Congridae), Zootaxa 4454 (1), pp. 215-227 : 217-220

Gavialiceps taiwanensis ( Chen & Weng, 1967)

Chlopsis taiwanensis Chen & Weng, 1967:81 , fig. 61 (type locality: Tungkang (=Dong-gang), southwestern Taiwan). Gavialiceps taiwanensis ( Chen & Weng, 1967) : Karmovskaya, 1993:73. Smith in Randall & Lim, 2000:586. Ho et al., 2010:25. Ho & Shao, 2011:24. Ho et al., 2015a:8. Ho et al., 2015b:150.

Diagnosis. Juveniles and adults with light grayish body color, skin transparent and body white, pale grayish dorsally, white ventrally; gill chamber and gill opening black. Predorsal vertebrae 6‒9; preanal vertebrae 46‒52; preanal lateral-line pores 46‒52; total vertebrae 225+; dorsal-fin rays before origin of anal fin 65‒72.

Leptocephali with body markedly attenuate, narrow, tape-like, with long and almost filamentous tail; body depth 3.2‒4.4% TL; pectoral fin absent; body devoid of pigment, except for row of 5 to 8 large melanophores along ventral margin. Total myomeres up to 227; predorsal myomeres 8‒99; and preanal myomeres 50‒134.

Description of Stage 1 ( Figs. 1A, 1B , 3A , 4A , 5A ). Largest specimen examined is 150+ mm TL (n=4). Total myomeres 173+‒203+ (n=2); predorsal myomeres 66 (n=1); and preanal myomeres 108‒111 (n=2). Head small, head length 5.1‒5.9% TL. Tip of snout bluntly pointed, no trace of expansion; extending slightly beyond tip of lower jaw anteriorly. Dorsal fin origin at about middle of body, predorsal length 42.0‒51.6% TL. Position of anus variable, slightly behind midpoint of body (57.6% TL) in a 150 mm specimen and at two-thirds of body (72.7% TL) in 149 mm specimen. Eye relatively large, 15.0‒18.3% HL; snout relatively short, 40.9‒45.4% HL; end of mouth gape below middle of eye, upper-jaw length 49.3‒57.3% HL. Complete data provided in Table 1.

Description of Stage 2 ( Figs. 1C , 3B , 5B ). Largest specimen examined is 144 mm TL (n=7). Total myomeres 164+‒227 (n=5); predorsal myomeres 13‒99 (n=3); and preanal myomeres 58‒134 (n=4). Head small, head length 5.5‒6.0% TL. Tip of snout more pointed than those of Stage 1 but no trace of expansion, extending well beyond tip of lower jaw anteriorly. Dorsal fin originating from near nape to behind middle of body, predorsal length 52.1‒61.5% TL. Position of anus variable, well behind middle of body, preanal length 44.5‒80.8% TL. Eye moderately large, 13.3‒19.7% HL; snout slightly longer than that of Stage 1, its length 45.4‒49.9% HL; end of mouth gape below middle to posterior margin of eye, upper-jaw length 49.5‒66.9% HL. Complete data provided in Table 1.

Description of Stage 3 ( Figs. 1D , 3C , 5C ). Largest specimen examined is 156+ mm TL (n=25). Total myomeres 152+‒212+ (n=15); predorsal myomeres 8‒77 (n=11); and preanal myomeres 50‒123 (n=14). Head small to moderately large, head length 6.4‒8.9% TL. Tip of snout pointed with clear expansion, extending well beyond tip of lower jaw anteriorly, just behind the expansion; a concavity on each side of snout forming a neck-like structure. Tip of lower jaw less expanded than that of upper jaw and not forming neck-like structure. Dorsal fin originating from near nape to about middle of body, predorsal length 10.4‒41.4% TL. Position of anus variable, at anterior third to three-fourths of body, preanal length 30.2‒64.3% TL. Eye relatively small, 12.4‒17.2% HL; snout slightly slender, 40.0‒55.9% HL; end of mouth gape below to slightly behind posterior margin of eye, upper-jaw length 49.8‒70.1% HL. Complete data provided in Table 1.

Description of juveniles ( Figs. 1E , 3D , 4B , 5D ). Body very slender, trunk somewhat cylindrical, with a filamentous tail; body depth 1.2‒2.7% TL. Head slightly shorter, head length 10.0% TL. Dorsal origin above or slightly behind gill opening. No pectoral fin. Anus at anterior two-fifths of the fish, preanal length 41.1% TL. Both jaws markedly slender with a rounded expansion at anterior tip; end of mouth gape well behind posterior margin of eye. Those large melanophores along ventral margin faded or absent; melanophores present along upper margin of vertebrae and dorsal surface of head; dorsal surface of body covered with tiny chromatophores; body less transparent. Complete data provided in Table 2.

Description of adults ( Figs. 2A, 2B , 3E , 4C , 5E ). Total vertebrae 201+‒225+ (n=9); predorsal vertebrae 6‒9; and preanal vertebrae 47‒52; predorsal lateral-line pores 5‒7; preanal lateral-line pores 46‒52; dorsal-fin rays before vertical through origin of anal fin 6 5‒72. Head small and slender, head length 8.2‒11.3% TL. Snout more slender than juveniles. Dorsal-fin origin above gill opening, predorsal length 8.3‒11.4% TL. No pectoral fin. Anus at anterior third to before middle of the fish, preanal length 30.3‒43.0% TL. Dorsal surface of head and body deep grayish; both upper and lower margins of vertebrae covered by dense melanophores; black color in gill chamber and surfaces of gut become obvious and can be observed in the semi-transparent body. Largest specimen with complete tail examined is 696 mm TL. Complete data provided in Table 2.

Figures

FIGURE 1. General appearance of G. taiwanensis. A, B. Stage 1, NMMB-P27898, 150 mm TL. C. Stage 2, NMMB-P27901, 137+ mm TL. D. Stage 3, NMMB-P27900, 144 mm TL E. Juvenile, NMMB-P27907, 72.4 mm PAL.

FIGURE 2. General appearance of G. taiwanensis. A. Adult, ASIZP 61770, 161.3 mm PAL. B. Adult, 208.1 mm PAL

FIGURE 3. Lateral view of head showing jaw development of G. taiwanensis. A. Stage 1, NMMB-P27898, 150 mm TL. B. Stage 2, NMMB-P27901, 137+ mm TL. C. Stage 3, NMMB-P27900, 144 mm TL. D. Juvenile, NMMB-P27907, 72.4 mm PAL. E. Adult, ASIZP61770, 161.3 mm PAL.

FIGURE 4. Dorsal view of head showing pigmentation of G. taiwanensis. A. Leptocephalus, NMMB-P27902, 150+ mm TL. B. Juvenile, NMMB-P27893, 103.2 mm PAL. C. Adult, NMMB-P2814, 172 mm PAL.

FIGURE 5. Close-up view of lateral side of body showing the pigmentation of G. taiwanensis. A. Stage 1, NMMB-P27898, 150 mm TL. B. Stage 2, NMMB-P27901, 137+ mm TL. C. Stage 3, NMMB-P27900, 144 mm TL. D. Juvenile, NMMB- P27893, 95.9 mm PAL. E. Adult, ASIZP 61770, 161.3 mm PAL.